Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/selfrefactor/rambda
Faster and smaller alternative to Ramda
https://github.com/selfrefactor/rambda
fp functional-programming lodash ramda utils
Last synced: about 1 month ago
JSON representation
Faster and smaller alternative to Ramda
- Host: GitHub
- URL: https://github.com/selfrefactor/rambda
- Owner: selfrefactor
- License: mit
- Created: 2017-01-15T13:50:45.000Z (over 7 years ago)
- Default Branch: master
- Last Pushed: 2024-04-24T10:00:48.000Z (about 1 month ago)
- Last Synced: 2024-04-24T15:13:58.857Z (about 1 month ago)
- Topics: fp, functional-programming, lodash, ramda, utils
- Language: JavaScript
- Homepage: https://selfrefactor.github.io/rambda
- Size: 12.3 MB
- Stars: 1,592
- Watchers: 15
- Forks: 85
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
Lists
- awesome-javascript - rambda - Faster and smaller alternative to *Ramda*. (Functional Programming / Runner)
- awesome-fp-js - Rambda - A faster alternative to Ramda in under 10kB. (Libraries)
- awesome-javascript-cn - rambda
- awesome-stars - selfrefactor/rambda - Faster and smaller alternative to Ramda (JavaScript)
- my-awesome-stars - rambda
- awesome-stars - selfrefactor/rambda - Faster and smaller alternative to Ramda (JavaScript)
- awesome-stars - selfrefactor/rambda - Faster and smaller alternative to Ramda (others)
- awesome-tiny-js - rambda - 187 tree-shakable helpers [(list).](https://bundlephobia.com/package/rambda) (Generic Utilities)
- awesome-javascript - rambda - Faster and smaller alternative to *Ramda*. (Functional Programming / Runner)
- awesome-javascript-builds-project - rambda - Faster and smaller alternative to *Ramda*. (Functional Programming / Runner)
- awesome-javascript - rambda
- awesome-javascript - rambda - Faster and smaller alternative to Ramda ` 📝 8 days ago ` (Functional Programming [🔝](#readme))
- awesome-stars - selfrefactor/rambda - Faster and smaller alternative to Ramda (JavaScript)
README
# Rambda
`Rambda` is smaller and faster alternative to the popular functional programming library **Ramda**. - [Documentation](https://selfrefactor.github.io/rambda/#/)
[](https://circleci.com/gh/selfrefactor/rambda/tree/master)
[](https://codecov.io/gh/selfrefactor/rambda)
[](https://packagephobia.com/result?p=rambda)
[](https://nest.land/package/rambda)
[](https://github.com/selfrefactor/rambda/pulls)
## ❯ Example use
```javascript
import { compose, map, filter } from 'rambda'
const result = compose(
map(x => x * 2),
filter(x => x > 2)
)([1, 2, 3, 4])
// => [6, 8]
```
You can test this example in Rambda's REPL
* [Differences between Rambda and Ramda](#differences-between-rambda-and-ramda)
* [API](#api)
* [Changelog](#-changelog)
[](#-example-use)
## ❯ Rambda's advantages
### TypeScript included
TypeScript definitions are included in the library, in comparison to **Ramda**, where you need to additionally install `@types/ramda`.
Still, you need to be aware that functional programming features in `TypeScript` are in development, which means that using **R.compose/R.pipe** can be problematic.
Important - Rambda version `7.1.0`(or higher) requires TypeScript version `4.3.3`(or higher).
### Understandable source code due to little usage of internals
`Ramda` uses a lot of internals, which hides a lot of logic. Reading the full source code of a method can be challenging.
### Better VSCode experience
If the project is written in Javascript, then `go to source definition` action will lead you to actual implementation of the method.
### Immutable TS definitions
You can use immutable version of Rambda definitions, which is linted with ESLint `functional/prefer-readonly-type` plugin.
```
import {add} from 'rambda/immutable'
```
### Deno support
Latest version of **Ramba** available for `Deno` users is 3 years old. This is not the case with **Rambda** as most of recent releases are available for `Deno` users.
Also, `Rambda` provides you with included TS definitions:
```
// Deno extension(https://marketplace.visualstudio.com/items?itemName=denoland.vscode-deno)
// is installed and initialized
import * as R from "https://deno.land/x/rambda/mod.ts";
import * as Ramda from "https://deno.land/x/ramda/mod.ts";
R.add(1)('foo') // => will trigger warning in VSCode as it should
Ramda.add(1)('foo') // => will not trigger warning in VSCode
```
### Dot notation for `R.path`, `R.paths`, `R.assocPath` and `R.lensPath`
Standard usage of `R.path` is `R.path(['a', 'b'], {a: {b: 1} })`.
In **Rambda** you have the choice to use dot notation(which is arguably more readable):
```
R.path('a.b', {a: {b: 1} })
```
### Comma notation for `R.pick` and `R.omit`
Similar to dot notation, but the separator is comma(`,`) instead of dot(`.`).
```
R.pick('a,b', {a: 1 , b: 2, c: 3} })
// No space allowed between properties
```
### Speed
**Rambda** is generally more performant than `Ramda` as the [benchmarks](#-benchmarks) can prove that.
### Support
One of the main issues with `Ramda` is the slow process of releasing new versions. This is not the case with **Rambda** as releases are made on regular basis.
[](#-rambdas-advantages)
## ❯ Missing Ramda methods
Click to see the full list of 51 Ramda methods not implemented in Rambda and their status.
- insert
- insertAll
- into
- invert
- invertObj
- invoker
- isNotNil
- keysIn
- lift
- liftN
- lt
- lte
- mapAccum
- mapAccumRight
- memoizeWith
- mergeDeepLeft
- mergeDeepWith
- mergeDeepWithKey
- mergeWithKey
- nAry
- nthArg
- o
- otherwise
- pair
- partialRight
- pathSatisfies
- pickBy
- pipeWith
- project
- promap
- reduceRight
- reduceWhile
- reduced
- remove
- scan
- sequence
- splitWhenever
- swap
- symmetricDifferenceWith
- andThen
- toPairsIn
- unary
- uncurryN
- unfold
- unionWith
- until
- useWith
- valuesIn
- xprod
- thunkify
- default
Most of above methods are in progress to be added to **Rambda**. The following methods are not going to be added:
- __ - placeholder method allows user to further customize the method call. While, it seems useful initially, the price is too high in terms of complexity for TypeScript definitions. If it is not easy exressable in TypeScript, it is not worth it as **Rambda** is a TypeScript first library.
- construct - Using classes is not very functional programming oriented.
- constructN - same as above
- transduce - currently is out of focus
- traverse - same as above
[](#-missing-ramda-methods)
## ❯ Install
- **yarn add rambda**
- For UMD usage either use `./dist/rambda.umd.js` or the following CDN link:
```
https://unpkg.com/rambda@CURRENT_VERSION/dist/rambda.umd.js
```
- with deno
```
import {add} from "https://deno.land/x/rambda/mod.ts";
```
[](#-install)
## Differences between Rambda and Ramda
- Rambda's **type** detects async functions and unresolved `Promises`. The returned values are `'Async'` and `'Promise'`.
- Rambda's **type** handles *NaN* input, in which case it returns `NaN`.
- Rambda's **forEach** can iterate over objects not only arrays.
- Rambda's **map**, **filter**, **partition** when they iterate over objects, they pass property and input object as predicate's argument.
- Rambda's **filter** returns empty array with bad input(`null` or `undefined`), while Ramda throws.
- Ramda's **clamp** work with strings, while Rambda's method work only with numbers.
- Ramda's **indexOf/lastIndexOf** work with strings and lists, while Rambda's method work only with lists as iterable input.
- Error handling, when wrong inputs are provided, may not be the same. This difference will be better documented once all brute force tests are completed.
- TypeScript definitions between `rambda` and `@types/ramda` may vary.
> If you need more **Ramda** methods in **Rambda**, you may either submit a `PR` or check the extended version of **Rambda** - [Rambdax](https://github.com/selfrefactor/rambdax). In case of the former, you may want to consult with [Rambda contribution guidelines.](CONTRIBUTING.md)
[](#-differences-between-rambda-and-ramda)
## ❯ Benchmarks
Click to expand all benchmark results
There are methods which are benchmarked only with `Ramda` and `Rambda`(i.e. no `Lodash`).
Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.
The benchmarks results are produced from latest versions of *Rambda*, *Lodash*(4.17.21) and *Ramda*(0.29.1).
method | Rambda | Ramda | Lodash
--- |--- | --- | ---
*add* | 🚀 Fastest | 21.52% slower | 82.15% slower
*adjust* | 8.48% slower | 🚀 Fastest | 🔳
*all* | 🚀 Fastest | 7.18% slower | 🔳
*allPass* | 🚀 Fastest | 88.25% slower | 🔳
*allPass* | 🚀 Fastest | 98.56% slower | 🔳
*and* | 🚀 Fastest | 89.09% slower | 🔳
*any* | 🚀 Fastest | 92.87% slower | 45.82% slower
*anyPass* | 🚀 Fastest | 98.25% slower | 🔳
*append* | 🚀 Fastest | 2.07% slower | 🔳
*applySpec* | 🚀 Fastest | 80.43% slower | 🔳
*assoc* | 72.32% slower | 60.08% slower | 🚀 Fastest
*clone* | 🚀 Fastest | 91.86% slower | 86.48% slower
*compose* | 6.07% slower | 16.89% slower | 🚀 Fastest
*converge* | 78.63% slower | 🚀 Fastest | 🔳
*curry* | 🚀 Fastest | 28.86% slower | 🔳
*curryN* | 🚀 Fastest | 41.05% slower | 🔳
*defaultTo* | 🚀 Fastest | 48.91% slower | 🔳
*drop* | 🚀 Fastest | 82.35% slower | 🔳
*dropLast* | 🚀 Fastest | 86.74% slower | 🔳
*equals* | 58.37% slower | 96.73% slower | 🚀 Fastest
*filter* | 6.7% slower | 72.03% slower | 🚀 Fastest
*find* | 🚀 Fastest | 85.14% slower | 42.65% slower
*findIndex* | 🚀 Fastest | 86.48% slower | 72.27% slower
*flatten* | 🚀 Fastest | 85.68% slower | 3.57% slower
*ifElse* | 🚀 Fastest | 58.56% slower | 🔳
*includes* | 🚀 Fastest | 81.64% slower | 🔳
*indexOf* | 🚀 Fastest | 80.17% slower | 🔳
*indexOf* | 🚀 Fastest | 82.2% slower | 🔳
*init* | 🚀 Fastest | 92.24% slower | 13.3% slower
*is* | 🚀 Fastest | 57.69% slower | 🔳
*isEmpty* | 🚀 Fastest | 97.14% slower | 54.99% slower
*last* | 🚀 Fastest | 93.43% slower | 5.28% slower
*lastIndexOf* | 🚀 Fastest | 85.19% slower | 🔳
*map* | 🚀 Fastest | 86.6% slower | 11.73% slower
*match* | 🚀 Fastest | 44.83% slower | 🔳
*merge* | 🚀 Fastest | 12.21% slower | 55.76% slower
*none* | 🚀 Fastest | 96.48% slower | 🔳
*objOf* | 🚀 Fastest | 38.05% slower | 🔳
*omit* | 🚀 Fastest | 69.95% slower | 97.34% slower
*over* | 🚀 Fastest | 56.23% slower | 🔳
*path* | 37.81% slower | 77.81% slower | 🚀 Fastest
*pick* | 🚀 Fastest | 19.07% slower | 80.2% slower
*pipe* | 🚀 Fastest | 0.11% slower | 🔳
*prop* | 🚀 Fastest | 87.95% slower | 🔳
*propEq* | 🚀 Fastest | 91.92% slower | 🔳
*range* | 🚀 Fastest | 61.8% slower | 57.44% slower
*reduce* | 60.48% slower | 77.1% slower | 🚀 Fastest
*repeat* | 48.57% slower | 68.98% slower | 🚀 Fastest
*replace* | 33.45% slower | 33.99% slower | 🚀 Fastest
*set* | 🚀 Fastest | 50.35% slower | 🔳
*sort* | 🚀 Fastest | 40.23% slower | 🔳
*sortBy* | 🚀 Fastest | 25.29% slower | 56.88% slower
*split* | 🚀 Fastest | 55.37% slower | 17.64% slower
*splitEvery* | 🚀 Fastest | 71.98% slower | 🔳
*take* | 🚀 Fastest | 91.96% slower | 4.72% slower
*takeLast* | 🚀 Fastest | 93.39% slower | 19.22% slower
*test* | 🚀 Fastest | 82.34% slower | 🔳
*type* | 🚀 Fastest | 48.6% slower | 🔳
*uniq* | 🚀 Fastest | 84.9% slower | 🔳
*uniqBy* | 51.93% slower | 🚀 Fastest | 🔳
*uniqWith* | 8.29% slower | 🚀 Fastest | 🔳
*uniqWith* | 14.23% slower | 🚀 Fastest | 🔳
*update* | 🚀 Fastest | 52.35% slower | 🔳
*view* | 🚀 Fastest | 76.15% slower | 🔳
[](#-benchmarks)
## ❯ Used by
- [ESLint plugin Mocha](https://www.npmjs.com/package/eslint-plugin-mocha)
- [WatermelonDB](https://github.com/Nozbe/WatermelonDB)
- [Walmart Canada](https://www.walmart.ca) reported by [w-b-dev](https://github.com/w-b-dev)
- [VSCode Slack integration](https://github.com/verydanny/vcslack)
- [Webpack PostCSS](https://github.com/sectsect/webpack-postcss)
- [MobX-State-Tree decorators](https://github.com/farwayer/mst-decorators)
- [Rewrite of the Betaflight configurator](https://github.com/freshollie/fresh-configurator)
- [MineFlayer plugin](https://github.com/G07cha/MineflayerArmorManager)
[](#-used-by)
## API
### add
It adds `a` and `b`.
Try this R.add example in Rambda REPL
[](#add)
### addIndex
Try this R.addIndex example in Rambda REPL
[](#addIndex)
### addIndexRight
Same as `R.addIndex`, but it will passed indexes are decreasing, instead of increasing.
[](#addIndexRight)
### adjust
```typescript
adjust(index: number, replaceFn: (x: T) => T, list: T[]): T[]
```
It replaces `index` in array `list` with the result of `replaceFn(list[i])`.
Try this R.adjust example in Rambda REPL
All TypeScript definitions
```typescript
adjust(index: number, replaceFn: (x: T) => T, list: T[]): T[];
adjust(index: number, replaceFn: (x: T) => T): (list: T[]) => T[];
```
R.adjust source
```javascript
import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'
function adjustFn(
index, replaceFn, list
){
const actualIndex = index < 0 ? list.length + index : index
if (index >= list.length || actualIndex < 0) return list
const clone = cloneList(list)
clone[ actualIndex ] = replaceFn(clone[ actualIndex ])
return clone
}
export const adjust = curry(adjustFn)
```
Tests
```javascript
import { add } from './add.js'
import { adjust } from './adjust.js'
import { pipe } from './pipe.js'
const list = [ 0, 1, 2 ]
const expected = [ 0, 11, 2 ]
test('happy', () => {})
test('happy', () => {
expect(adjust(
1, add(10), list
)).toEqual(expected)
})
test('with curring type 1 1 1', () => {
expect(adjust(1)(add(10))(list)).toEqual(expected)
})
test('with curring type 1 2', () => {
expect(adjust(1)(add(10), list)).toEqual(expected)
})
test('with curring type 2 1', () => {
expect(adjust(1, add(10))(list)).toEqual(expected)
})
test('with negative index', () => {
expect(adjust(
-2, add(10), list
)).toEqual(expected)
})
test('when index is out of bounds', () => {
const list = [ 0, 1, 2, 3 ]
expect(adjust(
4, add(1), list
)).toEqual(list)
expect(adjust(
-5, add(1), list
)).toEqual(list)
})
```
[](#adjust)
### all
```typescript
all(predicate: (x: T) => boolean, list: T[]): boolean
```
It returns `true`, if all members of array `list` returns `true`, when applied as argument to `predicate` function.
Try this R.all example in Rambda REPL
All TypeScript definitions
```typescript
all(predicate: (x: T) => boolean, list: T[]): boolean;
all(predicate: (x: T) => boolean): (list: T[]) => boolean;
```
R.all source
```javascript
export function all(predicate, list){
if (arguments.length === 1) return _list => all(predicate, _list)
for (let i = 0; i < list.length; i++){
if (!predicate(list[ i ])) return false
}
return true
}
```
Tests
```javascript
import { all } from './all.js'
const list = [ 0, 1, 2, 3, 4 ]
test('when true', () => {
const fn = x => x > -1
expect(all(fn)(list)).toBeTrue()
})
test('when false', () => {
const fn = x => x > 2
expect(all(fn, list)).toBeFalse()
})
```
TypeScript test
```typescript
import {all} from 'rambda'
describe('all', () => {
it('happy', () => {
const result = all(
x => {
x // $ExpectType number
return x > 0
},
[1, 2, 3]
)
result // $ExpectType boolean
})
it('curried needs a type', () => {
const result = all(x => {
x // $ExpectType number
return x > 0
})([1, 2, 3])
result // $ExpectType boolean
})
})
```
[](#all)
### allPass
```typescript
allPass(predicates: ((x: T) => boolean)[]): (input: T) => boolean
```
It returns `true`, if all functions of `predicates` return `true`, when `input` is their argument.
Try this R.allPass example in Rambda REPL
All TypeScript definitions
```typescript
allPass(predicates: ((x: T) => boolean)[]): (input: T) => boolean;
allPass(predicates: ((...inputs: T[]) => boolean)[]): (...inputs: T[]) => boolean;
```
R.allPass source
```javascript
export function allPass(predicates){
return (...input) => {
let counter = 0
while (counter < predicates.length){
if (!predicates[ counter ](...input)){
return false
}
counter++
}
return true
}
}
```
Tests
```javascript
import { allPass } from './allPass.js'
test('happy', () => {
const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ]
expect(allPass(rules)(11)).toBeTrue()
expect(allPass(rules)(undefined)).toBeFalse()
})
test('when returns true', () => {
const conditionArr = [ val => val.a === 1, val => val.b === 2 ]
expect(allPass(conditionArr)({
a : 1,
b : 2,
})).toBeTrue()
})
test('when returns false', () => {
const conditionArr = [ val => val.a === 1, val => val.b === 3 ]
expect(allPass(conditionArr)({
a : 1,
b : 2,
})).toBeFalse()
})
test('works with multiple inputs', () => {
const fn = function (
w, x, y, z
){
return w + x === y + z
}
expect(allPass([ fn ])(
3, 3, 3, 3
)).toBeTrue()
})
```
TypeScript test
```typescript
import {allPass, filter} from 'rambda'
describe('allPass', () => {
it('happy', () => {
const x = allPass([
y => {
y // $ExpectType number
return typeof y === 'number'
},
y => {
return y > 0
},
])(11)
x // $ExpectType boolean
})
it('issue #642', () => {
const isGreater = (num: number) => num > 5
const pred = allPass([isGreater])
const xs = [0, 1, 2, 3]
const filtered1 = filter(pred)(xs)
filtered1 // $ExpectType number[]
const filtered2 = xs.filter(pred)
filtered2 // $ExpectType number[]
})
it('issue #604', () => {
const plusEq = function(w: number, x: number, y: number, z: number) {
return w + x === y + z
}
const result = allPass([plusEq])(3, 3, 3, 3)
result // $ExpectType boolean
})
})
```
[](#allPass)
### always
It returns function that always returns `x`.
Try this R.always example in Rambda REPL
[](#always)
### and
Logical AND
Try this R.and example in Rambda REPL
[](#and)
### any
```typescript
any(predicate: (x: T) => boolean, list: T[]): boolean
```
It returns `true`, if at least one member of `list` returns true, when passed to a `predicate` function.
Try this R.any example in Rambda REPL
All TypeScript definitions
```typescript
any(predicate: (x: T) => boolean, list: T[]): boolean;
any(predicate: (x: T) => boolean): (list: T[]) => boolean;
```
R.any source
```javascript
export function any(predicate, list){
if (arguments.length === 1) return _list => any(predicate, _list)
let counter = 0
while (counter < list.length){
if (predicate(list[ counter ], counter)){
return true
}
counter++
}
return false
}
```
Tests
```javascript
import { any } from './any.js'
const list = [ 1, 2, 3 ]
test('happy', () => {
expect(any(x => x < 0, list)).toBeFalse()
})
test('with curry', () => {
expect(any(x => x > 2)(list)).toBeTrue()
})
```
TypeScript test
```typescript
import {any} from 'rambda'
describe('R.any', () => {
it('happy', () => {
const result = any(
x => {
x // $ExpectType number
return x > 2
},
[1, 2, 3]
)
result // $ExpectType boolean
})
it('when curried needs a type', () => {
const result = any(x => {
x // $ExpectType number
return x > 2
})([1, 2, 3])
result // $ExpectType boolean
})
})
```
[](#any)
### anyPass
```typescript
anyPass(predicates: ((x: T) => boolean)[]): (input: T) => boolean
```
It accepts list of `predicates` and returns a function. This function with its `input` will return `true`, if any of `predicates` returns `true` for this `input`.
Try this R.anyPass example in Rambda REPL
All TypeScript definitions
```typescript
anyPass(predicates: ((x: T) => boolean)[]): (input: T) => boolean;
anyPass(predicates: ((...inputs: T[]) => boolean)[]): (...inputs: T[]) => boolean;
```
R.anyPass source
```javascript
export function anyPass(predicates){
return (...input) => {
let counter = 0
while (counter < predicates.length){
if (predicates[ counter ](...input)){
return true
}
counter++
}
return false
}
}
```
Tests
```javascript
import { anyPass } from './anyPass.js'
test('happy', () => {
const rules = [ x => typeof x === 'string', x => x > 10 ]
const predicate = anyPass(rules)
expect(predicate('foo')).toBeTrue()
expect(predicate(6)).toBeFalse()
})
test('happy', () => {
const rules = [ x => typeof x === 'string', x => x > 10 ]
expect(anyPass(rules)(11)).toBeTrue()
expect(anyPass(rules)(undefined)).toBeFalse()
})
const obj = {
a : 1,
b : 2,
}
test('when returns true', () => {
const conditionArr = [ val => val.a === 1, val => val.a === 2 ]
expect(anyPass(conditionArr)(obj)).toBeTrue()
})
test('when returns false + curry', () => {
const conditionArr = [ val => val.a === 2, val => val.b === 3 ]
expect(anyPass(conditionArr)(obj)).toBeFalse()
})
test('with empty predicates list', () => {
expect(anyPass([])(3)).toBeFalse()
})
test('works with multiple inputs', () => {
const fn = function (
w, x, y, z
){
console.log(
w, x, y, z
)
return w + x === y + z
}
expect(anyPass([ fn ])(
3, 3, 3, 3
)).toBeTrue()
})
```
TypeScript test
```typescript
import {anyPass, filter} from 'rambda'
describe('anyPass', () => {
it('happy', () => {
const x = anyPass([
y => {
y // $ExpectType number
return typeof y === 'number'
},
y => {
return y > 0
},
])(11)
x // $ExpectType boolean
})
it('issue #604', () => {
const plusEq = function(w: number, x: number, y: number, z: number) {
return w + x === y + z
}
const result = anyPass([plusEq])(3, 3, 3, 3)
result // $ExpectType boolean
})
it('issue #642', () => {
const isGreater = (num: number) => num > 5
const pred = anyPass([isGreater])
const xs = [0, 1, 2, 3]
const filtered1 = filter(pred)(xs)
filtered1 // $ExpectType number[]
const filtered2 = xs.filter(pred)
filtered2 // $ExpectType number[]
})
it('functions as a type guard', () => {
const isString = (x: unknown): x is string => typeof x === 'string'
const isNumber = (x: unknown): x is number => typeof x === 'number'
const isBoolean = (x: unknown): x is boolean => typeof x === 'boolean'
const isStringNumberOrBoolean = anyPass([isString, isNumber, isBoolean])
isStringNumberOrBoolean // $ExpectType (input: unknown) => boolean
const aValue: unknown = 1
if (isStringNumberOrBoolean(aValue)) {
aValue // $ExpectType unknown
}
})
})
```
[](#anyPass)
### ap
```typescript
ap(fns: Array<(a: T) => U>[], vs: T[]): U[]
```
It takes a list of functions and a list of values. Then it returns a list of values obtained by applying each function to each value.
Try this R.ap example in Rambda REPL
All TypeScript definitions
```typescript
ap(fns: Array<(a: T) => U>[], vs: T[]): U[];
ap(fns: Array<(a: T) => U>): (vs: T[]) => U[];
ap(fn: (r: R, a: A) => B, fn1: (r: R) => A): (r: R) => B;
```
R.ap source
```javascript
export function ap(functions, input){
if (arguments.length === 1){
return _inputs => ap(functions, _inputs)
}
return functions.reduce((acc, fn) => [ ...acc, ...input.map(fn) ], [])
}
```
Tests
```javascript
import { ap } from './ap.js'
function mult2(x){
return x * 2
}
function plus3(x){
return x + 3
}
test('happy', () => {
expect(ap([ mult2, plus3 ], [ 1, 2, 3 ])).toEqual([ 2, 4, 6, 4, 5, 6 ])
})
```
[](#ap)
### aperture
```typescript
aperture(n: N, list: T[]): Array> | []
```
It returns a new list, composed of consecutive `n`-tuples from a `list`.
Try this R.aperture example in Rambda REPL
All TypeScript definitions
```typescript
aperture(n: N, list: T[]): Array> | [];
aperture(n: N): (list: T[]) => Array> | [];
```
R.aperture source
```javascript
export function aperture(step, list){
if (arguments.length === 1){
return _list => aperture(step, _list)
}
if (step > list.length) return []
let idx = 0
const limit = list.length - (step - 1)
const acc = new Array(limit)
while (idx < limit){
acc[ idx ] = list.slice(idx, idx + step)
idx += 1
}
return acc
}
```
Tests
```javascript
import { aperture } from './aperture.js'
const list = [ 1, 2, 3, 4, 5, 6, 7 ]
test('happy', () => {
expect(aperture(1, list)).toEqual([ [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ] ])
expect(aperture(2, list)).toEqual([
[ 1, 2 ],
[ 2, 3 ],
[ 3, 4 ],
[ 4, 5 ],
[ 5, 6 ],
[ 6, 7 ],
])
expect(aperture(3, list)).toEqual([
[ 1, 2, 3 ],
[ 2, 3, 4 ],
[ 3, 4, 5 ],
[ 4, 5, 6 ],
[ 5, 6, 7 ],
])
expect(aperture(8, list)).toEqual([])
})
```
[](#aperture)
### append
```typescript
append(xToAppend: T, iterable: T[]): T[]
```
It adds element `x` at the end of `iterable`.
Try this R.append example in Rambda REPL
All TypeScript definitions
```typescript
append(xToAppend: T, iterable: T[]): T[];
append(xToAppend: T, iterable: IsFirstSubtypeOfSecond[]) : U[];
append(xToAppend: T): (iterable: IsFirstSubtypeOfSecond[]) => U[];
append(xToAppend: T): (iterable: T[]) => T[];
```
R.append source
```javascript
import { cloneList } from './_internals/cloneList.js'
export function append(x, input){
if (arguments.length === 1) return _input => append(x, _input)
if (typeof input === 'string') return input.split('').concat(x)
const clone = cloneList(input)
clone.push(x)
return clone
}
```
Tests
```javascript
import { append } from './append.js'
test('happy', () => {
expect(append('tests', [ 'write', 'more' ])).toEqual([
'write',
'more',
'tests',
])
})
test('append to empty array', () => {
expect(append('tests')([])).toEqual([ 'tests' ])
})
test('with strings', () => {
expect(append('o', 'fo')).toEqual([ 'f', 'o', 'o' ])
})
```
TypeScript test
```typescript
import {append, prepend} from 'rambda'
const listOfNumbers = [1, 2, 3]
const listOfNumbersAndStrings = [1, 'b', 3]
describe('R.append/R.prepend', () => {
describe("with the same primitive type as the array's elements", () => {
it('uncurried', () => {
// @ts-expect-error
append('d', listOfNumbers)
// @ts-expect-error
prepend('d', listOfNumbers)
append(4, listOfNumbers) // $ExpectType number[]
prepend(4, listOfNumbers) // $ExpectType number[]
})
it('curried', () => {
// @ts-expect-error
append('d')(listOfNumbers)
append(4)(listOfNumbers) // $ExpectType number[]
prepend(4)(listOfNumbers) // $ExpectType number[]
})
})
describe("with a subtype of the array's elements", () => {
it('uncurried', () => {
// @ts-expect-error
append(true, listOfNumbersAndStrings)
append(4, listOfNumbersAndStrings) // $ExpectType (string | number)[]
prepend(4, listOfNumbersAndStrings) // $ExpectType (string | number)[]
})
it('curried', () => {
// @ts-expect-error
append(true)(listOfNumbersAndStrings)
append(4)(listOfNumbersAndStrings) // $ExpectType (string | number)[]
prepend(4)(listOfNumbersAndStrings) // $ExpectType (string | number)[]
})
})
describe("expanding the type of the array's elements", () => {
it('uncurried', () => {
// @ts-expect-error
append('d', listOfNumbers)
append('d', listOfNumbers) // $ExpectType (string | number)[]
prepend('d', listOfNumbers) // $ExpectType (string | number)[]
})
it('curried', () => {
// @ts-expect-error
append('d')(listOfNumbers)
const appendD = append('d')
appendD(listOfNumbers) // $ExpectType (string | number)[]
const prependD = prepend('d')
prependD(listOfNumbers) // $ExpectType (string | number)[]
})
})
})
```
[](#append)
### apply
```typescript
apply(fn: (...args: any[]) => T, args: any[]): T
```
It applies function `fn` to the list of arguments.
This is useful for creating a fixed-arity function from a variadic function. `fn` should be a bound function if context is significant.
Try this R.apply example in Rambda REPL
All TypeScript definitions
```typescript
apply(fn: (...args: any[]) => T, args: any[]): T;
apply(fn: (...args: any[]) => T): (args: any[]) => T;
```
R.apply source
```javascript
export function apply(fn, args){
if (arguments.length === 1){
return _args => apply(fn, _args)
}
return fn.apply(this, args)
}
```
Tests
```javascript
import { apply } from './apply.js'
import { bind } from './bind.js'
import { identity } from './identity.js'
test('happy', () => {
expect(apply(identity, [ 1, 2, 3 ])).toBe(1)
})
test('applies function to argument list', () => {
expect(apply(Math.max, [ 1, 2, 3, -99, 42, 6, 7 ])).toBe(42)
})
test('provides no way to specify context', () => {
const obj = {
method (){
return this === obj
},
}
expect(apply(obj.method, [])).toBeFalse()
expect(apply(bind(obj.method, obj), [])).toBeTrue()
})
```
TypeScript test
```typescript
import {apply, identity} from 'rambda'
describe('R.apply', () => {
it('happy', () => {
const result = apply(identity, [1, 2, 3])
result // $ExpectType number
})
it('curried', () => {
const fn = apply(identity)
const result = fn([1, 2, 3])
result // $ExpectType number
})
})
```
[](#apply)
### applySpec
```typescript
applySpec>(
spec: Spec
): (
...args: Parameters>
) => { [Key in keyof Spec]: ReturnType }
```
Try this R.applySpec example in Rambda REPL
All TypeScript definitions
```typescript
applySpec>(
spec: Spec
): (
...args: Parameters>
) => { [Key in keyof Spec]: ReturnType };
applySpec(spec: any): (...args: unknown[]) => T;
```
R.applySpec source
```javascript
import { isArray } from './_internals/isArray.js'
// recursively traverse the given spec object to find the highest arity function
export function __findHighestArity(spec, max = 0){
for (const key in spec){
if (spec.hasOwnProperty(key) === false || key === 'constructor') continue
if (typeof spec[ key ] === 'object'){
max = Math.max(max, __findHighestArity(spec[ key ]))
}
if (typeof spec[ key ] === 'function'){
max = Math.max(max, spec[ key ].length)
}
}
return max
}
function __filterUndefined(){
const defined = []
let i = 0
const l = arguments.length
while (i < l){
if (typeof arguments[ i ] === 'undefined') break
defined[ i ] = arguments[ i ]
i++
}
return defined
}
function __applySpecWithArity(
spec, arity, cache
){
const remaining = arity - cache.length
if (remaining === 1)
return x =>
__applySpecWithArity(
spec, arity, __filterUndefined(...cache, x)
)
if (remaining === 2)
return (x, y) =>
__applySpecWithArity(
spec, arity, __filterUndefined(
...cache, x, y
)
)
if (remaining === 3)
return (
x, y, z
) =>
__applySpecWithArity(
spec, arity, __filterUndefined(
...cache, x, y, z
)
)
if (remaining === 4)
return (
x, y, z, a
) =>
__applySpecWithArity(
spec,
arity,
__filterUndefined(
...cache, x, y, z, a
)
)
if (remaining > 4)
return (...args) =>
__applySpecWithArity(
spec, arity, __filterUndefined(...cache, ...args)
)
// handle spec as Array
if (isArray(spec)){
const ret = []
let i = 0
const l = spec.length
for (; i < l; i++){
// handle recursive spec inside array
if (typeof spec[ i ] === 'object' || isArray(spec[ i ])){
ret[ i ] = __applySpecWithArity(
spec[ i ], arity, cache
)
}
// apply spec to the key
if (typeof spec[ i ] === 'function'){
ret[ i ] = spec[ i ](...cache)
}
}
return ret
}
// handle spec as Object
const ret = {}
// apply callbacks to each property in the spec object
for (const key in spec){
if (spec.hasOwnProperty(key) === false || key === 'constructor') continue
// apply the spec recursively
if (typeof spec[ key ] === 'object'){
ret[ key ] = __applySpecWithArity(
spec[ key ], arity, cache
)
continue
}
// apply spec to the key
if (typeof spec[ key ] === 'function'){
ret[ key ] = spec[ key ](...cache)
}
}
return ret
}
export function applySpec(spec, ...args){
// get the highest arity spec function, cache the result and pass to __applySpecWithArity
const arity = __findHighestArity(spec)
if (arity === 0){
return () => ({})
}
const toReturn = __applySpecWithArity(
spec, arity, args
)
return toReturn
}
```
Tests
```javascript
import { applySpec as applySpecRamda, nAry } from 'ramda'
import {
add,
always,
compose,
dec,
inc,
map,
path,
prop,
T,
} from '../rambda.js'
import { applySpec } from './applySpec.js'
test('different than Ramda when bad spec', () => {
const result = applySpec({ sum : { a : 1 } })(1, 2)
const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2)
expect(result).toEqual({})
expect(ramdaResult).toEqual({ sum : { a : {} } })
})
test('works with empty spec', () => {
expect(applySpec({})()).toEqual({})
expect(applySpec([])(1, 2)).toEqual({})
expect(applySpec(null)(1, 2)).toEqual({})
})
test('works with unary functions', () => {
const result = applySpec({
v : inc,
u : dec,
})(1)
const expected = {
v : 2,
u : 0,
}
expect(result).toEqual(expected)
})
test('works with binary functions', () => {
const result = applySpec({ sum : add })(1, 2)
expect(result).toEqual({ sum : 3 })
})
test('works with nested specs', () => {
const result = applySpec({
unnested : always(0),
nested : { sum : add },
})(1, 2)
const expected = {
unnested : 0,
nested : { sum : 3 },
}
expect(result).toEqual(expected)
})
test('works with arrays of nested specs', () => {
const result = applySpec({
unnested : always(0),
nested : [ { sum : add } ],
})(1, 2)
expect(result).toEqual({
unnested : 0,
nested : [ { sum : 3 } ],
})
})
test('works with arrays of spec objects', () => {
const result = applySpec([ { sum : add } ])(1, 2)
expect(result).toEqual([ { sum : 3 } ])
})
test('works with arrays of functions', () => {
const result = applySpec([ map(prop('a')), map(prop('b')) ])([
{
a : 'a1',
b : 'b1',
},
{
a : 'a2',
b : 'b2',
},
])
const expected = [
[ 'a1', 'a2' ],
[ 'b1', 'b2' ],
]
expect(result).toEqual(expected)
})
test('works with a spec defining a map key', () => {
expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })
})
test('cannot retains the highest arity', () => {
const f = applySpec({
f1 : nAry(2, T),
f2 : nAry(5, T),
})
const fRamda = applySpecRamda({
f1 : nAry(2, T),
f2 : nAry(5, T),
})
expect(f).toHaveLength(0)
expect(fRamda).toHaveLength(5)
})
test('returns a curried function', () => {
expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })
})
// Additional tests
// ============================================
test('arity', () => {
const spec = {
one : x1 => x1,
two : (x1, x2) => x1 + x2,
three : (
x1, x2, x3
) => x1 + x2 + x3,
}
expect(applySpec(
spec, 1, 2, 3
)).toEqual({
one : 1,
two : 3,
three : 6,
})
})
test('arity over 5 arguments', () => {
const spec = {
one : x1 => x1,
two : (x1, x2) => x1 + x2,
three : (
x1, x2, x3
) => x1 + x2 + x3,
four : (
x1, x2, x3, x4
) => x1 + x2 + x3 + x4,
five : (
x1, x2, x3, x4, x5
) => x1 + x2 + x3 + x4 + x5,
}
expect(applySpec(
spec, 1, 2, 3, 4, 5
)).toEqual({
one : 1,
two : 3,
three : 6,
four : 10,
five : 15,
})
})
test('curried', () => {
const spec = {
one : x1 => x1,
two : (x1, x2) => x1 + x2,
three : (
x1, x2, x3
) => x1 + x2 + x3,
}
expect(applySpec(spec)(1)(2)(3)).toEqual({
one : 1,
two : 3,
three : 6,
})
})
test('curried over 5 arguments', () => {
const spec = {
one : x1 => x1,
two : (x1, x2) => x1 + x2,
three : (
x1, x2, x3
) => x1 + x2 + x3,
four : (
x1, x2, x3, x4
) => x1 + x2 + x3 + x4,
five : (
x1, x2, x3, x4, x5
) => x1 + x2 + x3 + x4 + x5,
}
expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
one : 1,
two : 3,
three : 6,
four : 10,
five : 15,
})
})
test('undefined property', () => {
const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) }
expect(applySpec(spec, {})).toEqual({ prop : undefined })
})
test('restructure json object', () => {
const spec = {
id : path('user.id'),
name : path('user.firstname'),
profile : path('user.profile'),
doesntExist : path('user.profile.doesntExist'),
info : { views : compose(inc, prop('views')) },
type : always('playa'),
}
const data = {
user : {
id : 1337,
firstname : 'john',
lastname : 'shaft',
profile : 'shaft69',
},
views : 42,
}
expect(applySpec(spec, data)).toEqual({
id : 1337,
name : 'john',
profile : 'shaft69',
doesntExist : undefined,
info : { views : 43 },
type : 'playa',
})
})
```
TypeScript test
```typescript
import {multiply, applySpec, inc, dec, add} from 'rambda'
describe('applySpec', () => {
it('ramda 1', () => {
const result = applySpec({
v: inc,
u: dec,
})(1)
result // $ExpectType { v: number; u: number; }
})
it('ramda 1', () => {
interface Output {
sum: number,
multiplied: number,
}
const result = applySpec({
sum: add,
multiplied: multiply,
})(1, 2)
result // $ExpectType Output
})
})
```
[](#applySpec)
### applyTo
Try this R.applyTo example in Rambda REPL
[](#applyTo)
### ascend
Try this R.ascend example in Rambda REPL
[](#ascend)
### assoc
It makes a shallow clone of `obj` with setting or overriding the property `prop` with `newValue`.
Try this R.assoc example in Rambda REPL
[](#assoc)
### assocPath
```typescript
assocPath(path: Path, newValue: any, obj: object): Output
```
It makes a shallow clone of `obj` with setting or overriding with `newValue` the property found with `path`.
Try this R.assocPath example in Rambda REPL
All TypeScript definitions
```typescript
assocPath(path: Path, newValue: any, obj: object): Output;
assocPath(path: Path, newValue: any): (obj: object) => Output;
assocPath(path: Path): (newValue: any) => (obj: object) => Output;
```
R.assocPath source
```javascript
import { cloneList } from './_internals/cloneList.js'
import { createPath } from './_internals/createPath.js'
import { isArray } from './_internals/isArray.js'
import { isIndexInteger } from './_internals/isInteger.js'
import { assocFn } from './assoc.js'
import { curry } from './curry.js'
export function assocPathFn(
path, newValue, input
){
const pathArrValue = createPath(path)
if (pathArrValue.length === 0) return newValue
const index = pathArrValue[ 0 ]
if (pathArrValue.length > 1){
const condition =
typeof input !== 'object' ||
input === null ||
!input.hasOwnProperty(index)
const nextInput = condition ?
isIndexInteger(pathArrValue[ 1 ]) ?
[] :
{} :
input[ index ]
newValue = assocPathFn(
Array.prototype.slice.call(pathArrValue, 1),
newValue,
nextInput
)
}
if (isIndexInteger(index) && isArray(input)){
const arr = cloneList(input)
arr[ index ] = newValue
return arr
}
return assocFn(
index, newValue, input
)
}
export const assocPath = curry(assocPathFn)
```
Tests
```javascript
import { assocPathFn } from './assocPath.js'
test.only('happy', () => {
const path = 'a.c.1'
const input = {
a : {
b : 1,
c : [ 1, 2 ],
},
}
assocPathFn(
path, 3, input
)
expect(input).toEqual({
a : {
b : 1,
c : [ 1, 2 ],
},
})
})
test('string can be used as path input', () => {
const testObj = {
a : [ { b : 1 }, { b : 2 } ],
d : 3,
}
const result1 = assocPathFn(
[ 'a', 0, 'b' ], 10, testObj
)
const result2 = assocPathFn(
'a.0.b', 10, testObj
)
const expected = {
a : [ { b : 10 }, { b : 2 } ],
d : 3,
}
expect(result1).toEqual(expected)
expect(result2).toEqual(expected)
})
test('difference with ramda - doesn\'t overwrite primitive values with keys in the path', () => {
const obj = { a : 'str' }
const result = assocPath(
[ 'a', 'b' ], 42, obj
)
expect(result).toEqual({
a : {
0 : 's',
1 : 't',
2 : 'r',
b : 42,
},
})
})
test('bug', () => {
/*
https://github.com/selfrefactor/rambda/issues/524
*/
const state = {}
const withDateLike = assocPath(
[ 'outerProp', '2020-03-10' ],
{ prop : 2 },
state
)
const withNumber = assocPath(
[ 'outerProp', '5' ], { prop : 2 }, state
)
const withDateLikeExpected = { outerProp : { '2020-03-10' : { prop : 2 } } }
const withNumberExpected = { outerProp : { 5 : { prop : 2 } } }
expect(withDateLike).toEqual(withDateLikeExpected)
expect(withNumber).toEqual(withNumberExpected)
})
test('adds a key to an empty object', () => {
expect(assocPath(
[ 'a' ], 1, {}
)).toEqual({ a : 1 })
})
test('adds a key to a non-empty object', () => {
expect(assocPath(
'b', 2, { a : 1 }
)).toEqual({
a : 1,
b : 2,
})
})
test('adds a nested key to a non-empty object', () => {
expect(assocPath(
'b.c', 2, { a : 1 }
)).toEqual({
a : 1,
b : { c : 2 },
})
})
test('adds a nested key to a nested non-empty object - curry case 1', () => {
expect(assocPath('b.d',
3)({
a : 1,
b : { c : 2 },
})).toEqual({
a : 1,
b : {
c : 2,
d : 3,
},
})
})
test('adds a key to a non-empty object - curry case 1', () => {
expect(assocPath('b', 2)({ a : 1 })).toEqual({
a : 1,
b : 2,
})
})
test('adds a nested key to a non-empty object - curry case 1', () => {
expect(assocPath('b.c', 2)({ a : 1 })).toEqual({
a : 1,
b : { c : 2 },
})
})
test('adds a key to a non-empty object - curry case 2', () => {
expect(assocPath('b')(2, { a : 1 })).toEqual({
a : 1,
b : 2,
})
})
test('adds a key to a non-empty object - curry case 3', () => {
const result = assocPath('b')(2)({ a : 1 })
expect(result).toEqual({
a : 1,
b : 2,
})
})
test('changes an existing key', () => {
expect(assocPath(
'a', 2, { a : 1 }
)).toEqual({ a : 2 })
})
test('undefined is considered an empty object', () => {
expect(assocPath(
'a', 1, undefined
)).toEqual({ a : 1 })
})
test('null is considered an empty object', () => {
expect(assocPath(
'a', 1, null
)).toEqual({ a : 1 })
})
test('value can be null', () => {
expect(assocPath(
'a', null, null
)).toEqual({ a : null })
})
test('value can be undefined', () => {
expect(assocPath(
'a', undefined, null
)).toEqual({ a : undefined })
})
test('assignment is shallow', () => {
expect(assocPath(
'a', { b : 2 }, { a : { c : 3 } }
)).toEqual({ a : { b : 2 } })
})
test('empty array as path', () => {
const result = assocPath(
[], 3, {
a : 1,
b : 2,
}
)
expect(result).toBe(3)
})
test('happy', () => {
const expected = { foo : { bar : { baz : 42 } } }
const result = assocPath(
[ 'foo', 'bar', 'baz' ], 42, { foo : null }
)
expect(result).toEqual(expected)
})
```
TypeScript test
```typescript
import {assocPath} from 'rambda'
interface Output {
a: number,
foo: {bar: number},
}
describe('R.assocPath - user must explicitly set type of output', () => {
it('with array as path input', () => {
const result = assocPath(['foo', 'bar'], 2, {a: 1})
result // $ExpectType Output
})
it('with string as path input', () => {
const result = assocPath('foo.bar', 2, {a: 1})
result // $ExpectType Output
})
})
describe('R.assocPath - curried', () => {
it('with array as path input', () => {
const result = assocPath(['foo', 'bar'], 2)({a: 1})
result // $ExpectType Output
})
it('with string as path input', () => {
const result = assocPath('foo.bar', 2)({a: 1})
result // $ExpectType Output
})
})
```
[](#assocPath)
### binary
Try this R.binary example in Rambda REPL
[](#binary)
### bind
```typescript
bind(fn: F, thisObj: T): (...args: Parameters) => ReturnType
```
Creates a function that is bound to a context.
Try this R.bind example in Rambda REPL
All TypeScript definitions
```typescript
bind(fn: F, thisObj: T): (...args: Parameters) => ReturnType;
bind(fn: F): (thisObj: T) => (...args: Parameters) => ReturnType;
```
R.bind source
```javascript
import { curryN } from './curryN.js'
export function bind(fn, thisObj){
if (arguments.length === 1){
return _thisObj => bind(fn, _thisObj)
}
return curryN(fn.length, (...args) => fn.apply(thisObj, args))
}
```
Tests
```javascript
import { bind } from './bind.js'
function Foo(x){
this.x = x
}
function add(x){
return this.x + x
}
function Bar(x, y){
this.x = x
this.y = y
}
Bar.prototype = new Foo()
Bar.prototype.getX = function (){
return 'prototype getX'
}
test('returns a function', () => {
expect(typeof bind(add)(Foo)).toBe('function')
})
test('returns a function bound to the specified context object', () => {
const f = new Foo(12)
function isFoo(){
return this instanceof Foo
}
const isFooBound = bind(isFoo, f)
expect(isFoo()).toBeFalse()
expect(isFooBound()).toBeTrue()
})
test('works with built-in types', () => {
const abc = bind(String.prototype.toLowerCase, 'ABCDEFG')
expect(typeof abc).toBe('function')
expect(abc()).toBe('abcdefg')
})
test('works with user-defined types', () => {
const f = new Foo(12)
function getX(){
return this.x
}
const getXFooBound = bind(getX, f)
expect(getXFooBound()).toBe(12)
})
test('works with plain objects', () => {
const pojso = { x : 100 }
function incThis(){
return this.x + 1
}
const incPojso = bind(incThis, pojso)
expect(typeof incPojso).toBe('function')
expect(incPojso()).toBe(101)
})
test('does not interfere with existing object methods', () => {
const b = new Bar('a', 'b')
function getX(){
return this.x
}
const getXBarBound = bind(getX, b)
expect(b.getX()).toBe('prototype getX')
expect(getXBarBound()).toBe('a')
})
test('preserves arity', () => {
const f0 = function (){
return 0
}
const f1 = function (a){
return a
}
const f2 = function (a, b){
return a + b
}
const f3 = function (
a, b, c
){
return a + b + c
}
expect(bind(f0, {})).toHaveLength(0)
expect(bind(f1, {})).toHaveLength(1)
expect(bind(f2, {})).toHaveLength(2)
expect(bind(f3, {})).toHaveLength(3)
})
```
TypeScript test
```typescript
import {bind} from 'rambda'
class Foo {}
function isFoo(this: T): boolean {
return this instanceof Foo
}
describe('R.bind', () => {
it('happy', () => {
const foo = new Foo()
const result = bind(isFoo, foo)()
result // $ExpectType boolean
})
})
```
[](#bind)
### both
```typescript
both(pred1: Pred, pred2: Pred): Pred
```
It returns a function with `input` argument.
This function will return `true`, if both `firstCondition` and `secondCondition` return `true` when `input` is passed as their argument.
Try this R.both example in Rambda REPL
All TypeScript definitions
```typescript
both(pred1: Pred, pred2: Pred): Pred;
both(pred1: Predicate, pred2: Predicate): Predicate;
both(pred1: Predicate): (pred2: Predicate) => Predicate;
both(pred1: Pred): (pred2: Pred) => Pred;
```
R.both source
```javascript
export function both(f, g){
if (arguments.length === 1) return _g => both(f, _g)
return (...input) => f(...input) && g(...input)
}
```
Tests
```javascript
import { both } from './both.js'
const firstFn = val => val > 0
const secondFn = val => val < 10
test('with curry', () => {
expect(both(firstFn)(secondFn)(17)).toBeFalse()
})
test('without curry', () => {
expect(both(firstFn, secondFn)(7)).toBeTrue()
})
test('with multiple inputs', () => {
const between = function (
a, b, c
){
return a < b && b < c
}
const total20 = function (
a, b, c
){
return a + b + c === 20
}
const fn = both(between, total20)
expect(fn(
5, 7, 8
)).toBeTrue()
})
test('skip evaluation of the second expression', () => {
let effect = 'not evaluated'
const F = function (){
return false
}
const Z = function (){
effect = 'Z got evaluated'
}
both(F, Z)()
expect(effect).toBe('not evaluated')
})
```
TypeScript test
```typescript
import {both} from 'rambda'
describe('R.both', () => {
it('with passed type', () => {
const fn = both(
x => x > 1,
x => x % 2 === 0
)
fn // $ExpectType Predicate
const result = fn(2) // $ExpectType boolean
result // $ExpectType boolean
})
it('with passed type - curried', () => {
const fn = both(x => x > 1)(x => x % 2 === 0)
fn // $ExpectType Predicate
const result = fn(2)
result // $ExpectType boolean
})
it('no type passed', () => {
const fn = both(
x => {
x // $ExpectType any
return x > 1
},
x => {
x // $ExpectType any
return x % 2 === 0
}
)
const result = fn(2)
result // $ExpectType boolean
})
it('no type passed - curried', () => {
const fn = both((x: number) => {
x // $ExpectType number
return x > 1
})((x: number) => {
x // $ExpectType number
return x % 2 === 0
})
const result = fn(2)
result // $ExpectType boolean
})
})
```
[](#both)
### call
Try this R.call example in Rambda REPL
[](#call)
### chain
```typescript
chain(fn: (n: T) => U[], list: T[]): U[]
```
The method is also known as `flatMap`.
Try this R.chain example in Rambda REPL
All TypeScript definitions
```typescript
chain(fn: (n: T) => U[], list: T[]): U[];
chain(fn: (n: T) => U[]): (list: T[]) => U[];
```
R.chain source
```javascript
export function chain(fn, list){
if (arguments.length === 1){
return _list => chain(fn, _list)
}
return [].concat(...list.map(fn))
}
```
Tests
```javascript
import { chain as chainRamda } from 'ramda'
import { chain } from './chain.js'
const duplicate = n => [ n, n ]
test('happy', () => {
const fn = x => [ x * 2 ]
const list = [ 1, 2, 3 ]
const result = chain(fn, list)
expect(result).toEqual([ 2, 4, 6 ])
})
test('maps then flattens one level', () => {
expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})
test('maps then flattens one level - curry', () => {
expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])
})
test('flattens only one level', () => {
const nest = n => [ [ n ] ]
expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])
})
test('can compose', () => {
function dec(x){
return [ x - 1 ]
}
function times2(x){
return [ x * 2 ]
}
const mdouble = chain(times2)
const mdec = chain(dec)
expect(mdec(mdouble([ 10, 20, 30 ]))).toEqual([ 19, 39, 59 ])
})
test('@types/ramda broken test', () => {
const score = {
maths : 90,
physics : 80,
}
const calculateTotal = score => {
const { maths, physics } = score
return maths + physics
}
const assocTotalToScore = (total, score) => ({
...score,
total,
})
const calculateAndAssocTotalToScore = chainRamda(assocTotalToScore,
calculateTotal)
expect(() =>
calculateAndAssocTotalToScore(score)).toThrowErrorMatchingInlineSnapshot('"fn(...) is not a function"')
})
```
TypeScript test
```typescript
import {chain} from 'rambda'
const list = [1, 2, 3]
const fn = (x: number) => [`${x}`, `${x}`]
describe('R.chain', () => {
it('without passing type', () => {
const result = chain(fn, list)
result // $ExpectType string[]
const curriedResult = chain(fn)(list)
curriedResult // $ExpectType string[]
})
})
```
[](#chain)
### clamp
Restrict a number `input` to be within `min` and `max` limits.
If `input` is bigger than `max`, then the result is `max`.
If `input` is smaller than `min`, then the result is `min`.
Try this R.clamp example in Rambda REPL
[](#clamp)
### clone
It creates a deep copy of the `input`, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.
Try this R.clone example in Rambda REPL
[](#clone)
### collectBy
Try this R.collectBy example in Rambda REPL
[](#collectBy)
### comparator
It returns a comparator function that can be used in `sort` method.
Try this R.comparator example in Rambda REPL
[](#comparator)
### complement
It returns `inverted` version of `origin` function that accept `input` as argument.
The return value of `inverted` is the negative boolean value of `origin(input)`.
Try this R.complement example in Rambda REPL
[](#complement)
### compose
It performs right-to-left function composition.
Try this R.compose example in Rambda REPL
[](#compose)
### composeWith
Try this R.composeWith example in Rambda REPL
[](#composeWith)
### concat
It returns a new string or array, which is the result of merging `x` and `y`.
Try this R.concat example in Rambda REPL
[](#concat)
### cond
It takes list with `conditions` and returns a new function `fn` that expects `input` as argument.
This function will start evaluating the `conditions` in order to find the first winner(order of conditions matter).
The winner is this condition, which left side returns `true` when `input` is its argument. Then the evaluation of the right side of the winner will be the final result.
If no winner is found, then `fn` returns `undefined`.
Try this R.cond example in Rambda REPL
[](#cond)
### converge
Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.
Try this R.converge example in Rambda REPL
[](#converge)
### count
It counts how many times `predicate` function returns `true`, when supplied with iteration of `list`.
Try this R.count example in Rambda REPL
[](#count)
### countBy
```typescript
countBy(transformFn: (x: T) => any, list: T[]): Record
```
It counts elements in a list after each instance of the input list is passed through `transformFn` function.
Try this R.countBy example in Rambda REPL
All TypeScript definitions
```typescript
countBy(transformFn: (x: T) => any, list: T[]): Record;
countBy(transformFn: (x: T) => any): (list: T[]) => Record;
```
R.countBy source
```javascript
export function countBy(fn, list){
if (arguments.length === 1){
return _list => countBy(fn, _list)
}
const willReturn = {}
list.forEach(item => {
const key = fn(item)
if (!willReturn[ key ]){
willReturn[ key ] = 1
} else {
willReturn[ key ]++
}
})
return willReturn
}
```
Tests
```javascript
import { countBy } from './countBy.js'
const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]
test('happy', () => {
const result = countBy(x => x.toLowerCase(), list)
expect(result).toEqual({
a : 2,
b : 2,
c : 2,
})
})
```
TypeScript test
```typescript
import {countBy} from 'rambda'
const transformFn = (x: string) => x.toLowerCase()
const list = ['a', 'A', 'b', 'B', 'c', 'C']
describe('R.countBy', () => {
it('happy', () => {
const result = countBy(transformFn, list)
result // $ExpectType Record
})
it('curried', () => {
const result = countBy(transformFn)(list)
result // $ExpectType Record
})
})
```
[](#countBy)
### curry
It expects a function as input and returns its curried version.
Try this R.curry example in Rambda REPL
[](#curry)
### curryN
It returns a curried equivalent of the provided function, with the specified arity.
[](#curryN)
### dec
It decrements a number.
Try this R.dec example in Rambda REPL
[](#dec)
### defaultTo
```typescript
defaultTo(defaultValue: T, input: T | null | undefined): T
```
It returns `defaultValue`, if all of `inputArguments` are `undefined`, `null` or `NaN`.
Else, it returns the first truthy `inputArguments` instance(from left to right).
Try this R.defaultTo example in Rambda REPL
All TypeScript definitions
```typescript
defaultTo(defaultValue: T, input: T | null | undefined): T;
defaultTo(defaultValue: T): (input: T | null | undefined) => T;
```
R.defaultTo source
```javascript
function isFalsy(input){
return (
input === undefined || input === null || Number.isNaN(input) === true
)
}
export function defaultTo(defaultArgument, input){
if (arguments.length === 1){
return _input => defaultTo(defaultArgument, _input)
}
return isFalsy(input) ? defaultArgument : input
}
```
Tests
```javascript
import { defaultTo } from './defaultTo.js'
test('with undefined', () => {
expect(defaultTo('foo')(undefined)).toBe('foo')
})
test('with null', () => {
expect(defaultTo('foo')(null)).toBe('foo')
})
test('with NaN', () => {
expect(defaultTo('foo')(NaN)).toBe('foo')
})
test('with empty string', () => {
expect(defaultTo('foo', '')).toBe('')
})
test('with false', () => {
expect(defaultTo('foo', false)).toBeFalse()
})
test('when inputArgument passes initial check', () => {
expect(defaultTo('foo', 'bar')).toBe('bar')
})
```
TypeScript test
```typescript
import {defaultTo} from 'rambda'
describe('R.defaultTo with Ramda spec', () => {
it('happy', () => {
const result = defaultTo('foo', '')
result // $ExpectType "" | "foo"
})
it('with explicit type', () => {
const result = defaultTo('foo', null)
result // $ExpectType string
})
})
```
[](#defaultTo)
### descend
Try this R.descend example in Rambda REPL
[](#descend)
### difference
```typescript
difference(a: T[], b: T[]): T[]
```
It returns the uniq set of all elements in the first list `a` not contained in the second list `b`.
`R.equals` is used to determine equality.
Try this R.difference example in Rambda REPL
All TypeScript definitions
```typescript
difference(a: T[], b: T[]): T[];
difference(a: T[]): (b: T[]) => T[];
```
R.difference source
```javascript
import { includes } from './includes.js'
import { uniq } from './uniq.js'
export function difference(a, b){
if (arguments.length === 1) return _b => difference(a, _b)
return uniq(a).filter(aInstance => !includes(aInstance, b))
}
```
Tests
```javascript
import { difference as differenceRamda } from 'ramda'
import { difference } from './difference.js'
test('difference', () => {
const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]
expect(difference(a)(b)).toEqual([ 1, 2 ])
expect(difference([], [])).toEqual([])
})
test('difference with objects', () => {
const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])
})
test('no duplicates in first list', () => {
const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ]
const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ]
expect(difference(M2, N2)).toEqual([ 1, 2 ])
})
test('should use R.equals', () => {
expect(difference([ 1 ], [ 1 ])).toHaveLength(0)
expect(differenceRamda([ NaN ], [ NaN ])).toHaveLength(0)
})
```
TypeScript test
```typescript
import {difference} from 'rambda'
const list1 = [1, 2, 3]
const list2 = [1, 2, 4]
describe('R.difference', () => {
it('happy', () => {
const result = difference(list1, list2)
result // $ExpectType number[]
})
it('curried', () => {
const result = difference(list1)(list2)
result // $ExpectType number[]
})
})
```
[](#difference)
### differenceWith
```typescript
differenceWith(
pred: (a: T1, b: T2) => boolean,
list1: T1[],
list2: T2[],
): T1[]
```
Try this R.differenceWith example in Rambda REPL
All TypeScript definitions
```typescript
differenceWith(
pred: (a: T1, b: T2) => boolean,
list1: T1[],
list2: T2[],
): T1[];
differenceWith(
pred: (a: T1, b: T2) => boolean,
): (list1: T1[], list2: T2[]) => T1[];
differenceWith(
pred: (a: T1, b: T2) => boolean,
list1: T1[],
): (list2: T2[]) => T1[];
```
R.differenceWith source
```javascript
import { curry } from './curry.js'
import { _indexOf } from './equals.js'
export function differenceWithFn(
fn, a, b
){
const willReturn = []
const [ first, second ] = a.length > b.length ? [ a, b ] : [ b, a ]
first.forEach(item => {
const hasItem = second.some(secondItem => fn(item, secondItem))
if (!hasItem && _indexOf(item, willReturn) === -1){
willReturn.push(item)
}
})
return willReturn
}
export const differenceWith = curry(differenceWithFn)
```
Tests
```javascript
import { differenceWith } from './differenceWith.js'
test('happy', () => {
const foo = [ { a : 1 }, { a : 2 }, { a : 3 } ]
const bar = [ { a : 3 }, { a : 4 } ]
const fn = function (r, s){
return r.a === s.a
}
const result = differenceWith(
fn, foo, bar
)
expect(result).toEqual([ { a : 1 }, { a : 2 } ])
})
```
[](#differenceWith)
### dissoc
It returns a new object that does not contain property `prop`.
Try this R.dissoc example in Rambda REPL
[](#dissoc)
### dissocPath
Try this R.dissocPath example in Rambda REPL
[](#dissocPath)
### divide
Try this R.divide example in Rambda REPL
[](#divide)
### drop
```typescript
drop(howMany: number, input: T[]): T[]
```
It returns `howMany` items dropped from beginning of list or string `input`.
Try this R.drop example in Rambda REPL
All TypeScript definitions
```typescript
drop(howMany: number, input: T[]): T[];
drop(howMany: number, input: string): string;
drop(howMany: number): {
(input: T[]): T[];
(input: string): string;
};
```
R.drop source
```javascript
export function drop(howManyToDrop, listOrString){
if (arguments.length === 1) return _list => drop(howManyToDrop, _list)
return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)
}
```
Tests
```javascript
import assert from 'assert'
import { drop } from './drop.js'
test('with array', () => {
expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})
test('with string', () => {
expect(drop(3, 'rambda')).toBe('bda')
})
test('with non-positive count', () => {
expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})
test('should return copy', () => {
const xs = [ 1, 2, 3 ]
assert.notStrictEqual(drop(0, xs), xs)
assert.notStrictEqual(drop(-1, xs), xs)
})
```
TypeScript test
```typescript
import {drop} from 'rambda'
const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2
describe('R.drop - array', () => {
it('happy', () => {
const result = drop(howMany, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = drop(howMany)(list)
result // $ExpectType number[]
})
})
describe('R.drop - string', () => {
it('happy', () => {
const result = drop(howMany, str)
result // $ExpectType string
})
it('curried', () => {
const result = drop(howMany)(str)
result // $ExpectType string
})
})
```
[](#drop)
### dropLast
```typescript
dropLast(howMany: number, input: T[]): T[]
```
It returns `howMany` items dropped from the end of list or string `input`.
Try this R.dropLast example in Rambda REPL
All TypeScript definitions
```typescript
dropLast(howMany: number, input: T[]): T[];
dropLast(howMany: number, input: string): string;
dropLast(howMany: number): {
(input: T[]): T[];
(input: string): string;
};
```
R.dropLast source
```javascript
export function dropLast(howManyToDrop, listOrString){
if (arguments.length === 1){
return _listOrString => dropLast(howManyToDrop, _listOrString)
}
return howManyToDrop > 0 ?
listOrString.slice(0, -howManyToDrop) :
listOrString.slice()
}
```
Tests
```javascript
import assert from 'assert'
import { dropLast } from './dropLast.js'
test('with array', () => {
expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ])
expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([])
expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])
})
test('with string', () => {
expect(dropLast(3, 'rambda')).toBe('ram')
})
test('with non-positive count', () => {
expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})
test('should return copy', () => {
const xs = [ 1, 2, 3 ]
assert.notStrictEqual(dropLast(0, xs), xs)
assert.notStrictEqual(dropLast(-1, xs), xs)
})
```
TypeScript test
```typescript
import {dropLast} from 'rambda'
const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2
describe('R.dropLast - array', () => {
it('happy', () => {
const result = dropLast(howMany, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = dropLast(howMany)(list)
result // $ExpectType number[]
})
})
describe('R.dropLast - string', () => {
it('happy', () => {
const result = dropLast(howMany, str)
result // $ExpectType string
})
it('curried', () => {
const result = dropLast(howMany)(str)
result // $ExpectType string
})
})
```
[](#dropLast)
### dropLastWhile
Try this R.dropLastWhile example in Rambda REPL
[](#dropLastWhile)
### dropRepeats
```typescript
dropRepeats(list: T[]): T[]
```
It removes any successive duplicates according to `R.equals`.
Try this R.dropRepeats example in Rambda REPL
All TypeScript definitions
```typescript
dropRepeats(list: T[]): T[];
```
R.dropRepeats source
```javascript
import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'
export function dropRepeats(list){
if (!isArray(list)){
throw new Error(`${ list } is not a list`)
}
const toReturn = []
list.reduce((prev, current) => {
if (!equals(prev, current)){
toReturn.push(current)
}
return current
}, undefined)
return toReturn
}
```
Tests
```javascript
import { dropRepeats as dropRepeatsRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'
import { add } from './add.js'
import { dropRepeats } from './dropRepeats.js'
const list = [ 1, 2, 2, 2, 3, 4, 4, 5, 5, 3, 2, 2, { a : 1 }, { a : 1 } ]
const listClean = [ 1, 2, 3, 4, 5, 3, 2, { a : 1 } ]
test('happy', () => {
const result = dropRepeats(list)
expect(result).toEqual(listClean)
})
const possibleLists = [
[ add(1), async () => {}, [ 1 ], [ 1 ], [ 2 ], [ 2 ] ],
[ add(1), add(1), add(2) ],
[],
1,
/foo/g,
Promise.resolve(1),
]
describe('brute force', () => {
compareCombinations({
firstInput : possibleLists,
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 0,
"RESULTS_MISMATCH": 1,
"SHOULD_NOT_THROW": 3,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 6,
}
`)
},
fn : dropRepeats,
fnRamda : dropRepeatsRamda,
})
})
```
TypeScript test
```typescript
import {dropRepeats} from 'rambda'
describe('R.dropRepeats', () => {
it('happy', () => {
const result = dropRepeats([1, 2, 2, 3])
result // $ExpectType number[]
})
})
```
[](#dropRepeats)
### dropRepeatsBy
Try this R.dropRepeatsBy example in Rambda REPL
[](#dropRepeatsBy)
### dropRepeatsWith
Try this R.dropRepeatsWith example in Rambda REPL
[](#dropRepeatsWith)
### dropWhile
Try this R.dropWhile example in Rambda REPL
[](#dropWhile)
### either
```typescript
either(firstPredicate: Pred, secondPredicate: Pred): Pred
```
It returns a new `predicate` function from `firstPredicate` and `secondPredicate` inputs.
This `predicate` function will return `true`, if any of the two input predicates return `true`.
Try this R.either example in Rambda REPL
All TypeScript definitions
```typescript
either(firstPredicate: Pred, secondPredicate: Pred): Pred;
either(firstPredicate: Predicate, secondPredicate: Predicate): Predicate;
either(firstPredicate: Predicate): (secondPredicate: Predicate) => Predicate;
either(firstPredicate: Pred): (secondPredicate: Pred) => Pred;
```
R.either source
```javascript
export function either(firstPredicate, secondPredicate){
if (arguments.length === 1){
return _secondPredicate => either(firstPredicate, _secondPredicate)
}
return (...input) =>
Boolean(firstPredicate(...input) || secondPredicate(...input))
}
```
Tests
```javascript
import { either } from './either.js'
test('with multiple inputs', () => {
const between = function (
a, b, c
){
return a < b && b < c
}
const total20 = function (
a, b, c
){
return a + b + c === 20
}
const fn = either(between, total20)
expect(fn(
7, 8, 5
)).toBeTrue()
})
test('skip evaluation of the second expression', () => {
let effect = 'not evaluated'
const F = function (){
return true
}
const Z = function (){
effect = 'Z got evaluated'
}
either(F, Z)()
expect(effect).toBe('not evaluated')
})
test('case 1', () => {
const firstFn = val => val > 0
const secondFn = val => val * 5 > 10
expect(either(firstFn, secondFn)(1)).toBeTrue()
})
test('case 2', () => {
const firstFn = val => val > 0
const secondFn = val => val === -10
const fn = either(firstFn)(secondFn)
expect(fn(-10)).toBeTrue()
})
```
TypeScript test
```typescript
import {either} from 'rambda'
describe('R.either', () => {
it('with passed type', () => {
const fn = either(
x => x > 1,
x => x % 2 === 0
)
fn // $ExpectType Predicate
const result = fn(2) // $ExpectType boolean
result // $ExpectType boolean
})
it('with passed type - curried', () => {
const fn = either(x => x > 1)(x => x % 2 === 0)
fn // $ExpectType Predicate
const result = fn(2)
result // $ExpectType boolean
})
it('no type passed', () => {
const fn = either(
x => {
x // $ExpectType any
return x > 1
},
x => {
x // $ExpectType any
return x % 2 === 0
}
)
const result = fn(2)
result // $ExpectType boolean
})
it('no type passed - curried', () => {
const fn = either((x: number) => {
x // $ExpectType number
return x > 1
})((x: number) => {
x // $ExpectType number
return x % 2 === 0
})
const result = fn(2)
result // $ExpectType boolean
})
})
```
[](#either)
### empty
Try this R.empty example in Rambda REPL
[](#empty)
### endsWith
```typescript
endsWith(question: T, str: string): boolean
```
When iterable is a string, then it behaves as `String.prototype.endsWith`.
When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.
Try this R.endsWith example in Rambda REPL
All TypeScript definitions
```typescript
endsWith(question: T, str: string): boolean;
endsWith(question: T): (str: string) => boolean;
endsWith(question: T[], list: T[]): boolean;
endsWith(question: T[]): (list: T[]) => boolean;
```
R.endsWith source
```javascript
import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'
export function endsWith(target, iterable){
if (arguments.length === 1) return _iterable => endsWith(target, _iterable)
if (typeof iterable === 'string'){
return iterable.endsWith(target)
}
if (!isArray(target)) return false
const diff = iterable.length - target.length
let correct = true
const filtered = target.filter((x, index) => {
if (!correct) return false
const result = equals(x, iterable[ index + diff ])
if (!result) correct = false
return result
})
return filtered.length === target.length
}
```
Tests
```javascript
import { endsWith as endsWithRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'
import { endsWith } from './endsWith.js'
test('with string', () => {
expect(endsWith('bar', 'foo-bar')).toBeTrue()
expect(endsWith('baz')('foo-bar')).toBeFalse()
})
test('use R.equals with array', () => {
const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
expect(endsWith({ a : 3 }, list)).toBeFalse(),
expect(endsWith([ { a : 3 } ], list)).toBeTrue()
expect(endsWith([ { a : 2 }, { a : 3 } ], list)).toBeTrue()
expect(endsWith(list, list)).toBeTrue()
expect(endsWith([ { a : 1 } ], list)).toBeFalse()
})
export const possibleTargets = [
NaN,
[ NaN ],
/foo/,
[ /foo/ ],
Promise.resolve(1),
[ Promise.resolve(1) ],
Error('foo'),
[ Error('foo') ],
]
export const possibleIterables = [
[ Promise.resolve(1), Promise.resolve(2) ],
[ /foo/, /bar/ ],
[ NaN ],
[ Error('foo'), Error('bar') ],
]
describe('brute force', () => {
compareCombinations({
fn : endsWith,
fnRamda : endsWithRamda,
firstInput : possibleTargets,
secondInput : possibleIterables,
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 0,
"RESULTS_MISMATCH": 0,
"SHOULD_NOT_THROW": 0,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 32,
}
`)
},
})
})
```
TypeScript test
```typescript
import {endsWith} from 'rambda'
describe('R.endsWith - array', () => {
const target = [{a: 2}]
const input = [{a: 1}, {a: 2}]
it('happy', () => {
const result = endsWith(target, input)
result // $ExpectType boolean
})
it('curried', () => {
const result = endsWith(target)(input)
result // $ExpectType boolean
})
})
describe('R.endsWith - string', () => {
const target = 'bar'
const input = 'foo bar'
it('happy', () => {
const result = endsWith(target, input)
result // $ExpectType boolean
})
it('curried', () => {
const result = endsWith(target)(input)
result // $ExpectType boolean
})
})
```
[](#endsWith)
### eqBy
Try this R.eqBy example in Rambda REPL
[](#eqBy)
### eqProps
It returns `true` if property `prop` in `obj1` is equal to property `prop` in `obj2` according to `R.equals`.
Try this R.eqProps example in Rambda REPL
[](#eqProps)
### equals
```typescript
equals(x: T, y: T): boolean
```
It deeply compares `x` and `y` and returns `true` if they are equal.
Try this R.equals example in Rambda REPL
All TypeScript definitions
```typescript
equals(x: T, y: T): boolean;
equals(x: T): (y: T) => boolean;
```
R.equals source
```javascript
import { isArray } from './_internals/isArray.js'
import { type } from './type.js'
export function _lastIndexOf(valueToFind, list){
if (!isArray(list))
throw new Error(`Cannot read property 'indexOf' of ${ list }`)
const typeOfValue = type(valueToFind)
if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
return list.lastIndexOf(valueToFind)
const { length } = list
let index = length
let foundIndex = -1
while (--index > -1 && foundIndex === -1)
if (equals(list[ index ], valueToFind))
foundIndex = index
return foundIndex
}
export function _indexOf(valueToFind, list){
if (!isArray(list))
throw new Error(`Cannot read property 'indexOf' of ${ list }`)
const typeOfValue = type(valueToFind)
if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue))
return list.indexOf(valueToFind)
let index = -1
let foundIndex = -1
const { length } = list
while (++index < length && foundIndex === -1)
if (equals(list[ index ], valueToFind))
foundIndex = index
return foundIndex
}
function _arrayFromIterator(iter){
const list = []
let next
while (!(next = iter.next()).done)
list.push(next.value)
return list
}
function _compareSets(a, b){
if (a.size !== b.size)
return false
const aList = _arrayFromIterator(a.values())
const bList = _arrayFromIterator(b.values())
const filtered = aList.filter(aInstance => _indexOf(aInstance, bList) === -1)
return filtered.length === 0
}
function compareErrors(a, b){
if (a.message !== b.message) return false
if (a.toString !== b.toString) return false
return a.toString() === b.toString()
}
function parseDate(maybeDate){
if (!maybeDate.toDateString) return [ false ]
return [ true, maybeDate.getTime() ]
}
function parseRegex(maybeRegex){
if (maybeRegex.constructor !== RegExp) return [ false ]
return [ true, maybeRegex.toString() ]
}
export function equals(a, b){
if (arguments.length === 1) return _b => equals(a, _b)
const aType = type(a)
if (aType !== type(b)) return false
if (aType === 'Function')
return a.name === undefined ? false : a.name === b.name
if ([ 'NaN', 'Null', 'Undefined' ].includes(aType)) return true
if ([ 'BigInt', 'Number' ].includes(aType)){
if (Object.is(-0, a) !== Object.is(-0, b)) return false
return a.toString() === b.toString()
}
if ([ 'Boolean', 'String' ].includes(aType))
return a.toString() === b.toString()
if (aType === 'Array'){
const aClone = Array.from(a)
const bClone = Array.from(b)
if (aClone.toString() !== bClone.toString())
return false
let loopArrayFlag = true
aClone.forEach((aCloneInstance, aCloneIndex) => {
if (loopArrayFlag)
if (
aCloneInstance !== bClone[ aCloneIndex ] &&
!equals(aCloneInstance, bClone[ aCloneIndex ])
)
loopArrayFlag = false
})
return loopArrayFlag
}
const aRegex = parseRegex(a)
const bRegex = parseRegex(b)
if (aRegex[ 0 ])
return bRegex[ 0 ] ? aRegex[ 1 ] === bRegex[ 1 ] : false
else if (bRegex[ 0 ]) return false
const aDate = parseDate(a)
const bDate = parseDate(b)
if (aDate[ 0 ])
return bDate[ 0 ] ? aDate[ 1 ] === bDate[ 1 ] : false
else if (bDate[ 0 ]) return false
if (a instanceof Error){
if (!(b instanceof Error)) return false
return compareErrors(a, b)
}
if (aType === 'Set')
return _compareSets(a, b)
if (aType === 'Object'){
const aKeys = Object.keys(a)
if (aKeys.length !== Object.keys(b).length)
return false
let loopObjectFlag = true
aKeys.forEach(aKeyInstance => {
if (loopObjectFlag){
const aValue = a[ aKeyInstance ]
const bValue = b[ aKeyInstance ]
if (aValue !== bValue && !equals(aValue, bValue))
loopObjectFlag = false
}
})
return loopObjectFlag
}
return false
}
```
Tests
```javascript
import { equals as equalsRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'
import { variousTypes } from './benchmarks/_utils.js'
import { equals } from './equals.js'
test('compare functions', () => {
function foo(){}
function bar(){}
const baz = () => {}
const expectTrue = equals(foo, foo)
const expectFalseFirst = equals(foo, bar)
const expectFalseSecond = equals(foo, baz)
expect(expectTrue).toBeTrue()
expect(expectFalseFirst).toBeFalse()
expect(expectFalseSecond).toBeFalse()
})
test('with array of objects', () => {
const list1 = [ { a : 1 }, [ { b : 2 } ] ]
const list2 = [ { a : 1 }, [ { b : 2 } ] ]
const list3 = [ { a : 1 }, [ { b : 3 } ] ]
expect(equals(list1, list2)).toBeTrue()
expect(equals(list1, list3)).toBeFalse()
})
test('with regex', () => {
expect(equals(/s/, /s/)).toBeTrue()
expect(equals(/s/, /d/)).toBeFalse()
expect(equals(/a/gi, /a/gi)).toBeTrue()
expect(equals(/a/gim, /a/gim)).toBeTrue()
expect(equals(/a/gi, /a/i)).toBeFalse()
})
test('not a number', () => {
expect(equals([ NaN ], [ NaN ])).toBeTrue()
})
test('new number', () => {
expect(equals(new Number(0), new Number(0))).toBeTrue()
expect(equals(new Number(0), new Number(1))).toBeFalse()
expect(equals(new Number(1), new Number(0))).toBeFalse()
})
test('new string', () => {
expect(equals(new String(''), new String(''))).toBeTrue()
expect(equals(new String(''), new String('x'))).toBeFalse()
expect(equals(new String('x'), new String(''))).toBeFalse()
expect(equals(new String('foo'), new String('foo'))).toBeTrue()
expect(equals(new String('foo'), new String('bar'))).toBeFalse()
expect(equals(new String('bar'), new String('foo'))).toBeFalse()
})
test('new Boolean', () => {
expect(equals(new Boolean(true), new Boolean(true))).toBeTrue()
expect(equals(new Boolean(false), new Boolean(false))).toBeTrue()
expect(equals(new Boolean(true), new Boolean(false))).toBeFalse()
expect(equals(new Boolean(false), new Boolean(true))).toBeFalse()
})
test('new Error', () => {
expect(equals(new Error('XXX'), {})).toBeFalse()
expect(equals(new Error('XXX'), new TypeError('XXX'))).toBeFalse()
expect(equals(new Error('XXX'), new Error('YYY'))).toBeFalse()
expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
expect(equals(new Error('XXX'), new TypeError('YYY'))).toBeFalse()
expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()
})
test('with dates', () => {
expect(equals(new Date(0), new Date(0))).toBeTrue()
expect(equals(new Date(1), new Date(1))).toBeTrue()
expect(equals(new Date(0), new Date(1))).toBeFalse()
expect(equals(new Date(1), new Date(0))).toBeFalse()
expect(equals(new Date(0), {})).toBeFalse()
expect(equals({}, new Date(0))).toBeFalse()
})
test('ramda spec', () => {
expect(equals({}, {})).toBeTrue()
expect(equals({
a : 1,
b : 2,
},
{
a : 1,
b : 2,
})).toBeTrue()
expect(equals({
a : 2,
b : 3,
},
{
a : 2,
b : 3,
})).toBeTrue()
expect(equals({
a : 2,
b : 3,
},
{
a : 3,
b : 3,
})).toBeFalse()
expect(equals({
a : 2,
b : 3,
c : 1,
},
{
a : 2,
b : 3,
})).toBeFalse()
})
test('works with boolean tuple', () => {
expect(equals([ true, false ], [ true, false ])).toBeTrue()
expect(equals([ true, false ], [ true, true ])).toBeFalse()
})
test('works with equal objects within array', () => {
const objFirst = {
a : {
b : 1,
c : 2,
d : [ 1 ],
},
}
const objSecond = {
a : {
b : 1,
c : 2,
d : [ 1 ],
},
}
const x = [ 1, 2, objFirst, null, '', [] ]
const y = [ 1, 2, objSecond, null, '', [] ]
expect(equals(x, y)).toBeTrue()
})
test('works with different objects within array', () => {
const objFirst = { a : { b : 1 } }
const objSecond = { a : { b : 2 } }
const x = [ 1, 2, objFirst, null, '', [] ]
const y = [ 1, 2, objSecond, null, '', [] ]
expect(equals(x, y)).toBeFalse()
})
test('works with undefined as second argument', () => {
expect(equals(1, undefined)).toBeFalse()
expect(equals(undefined, undefined)).toBeTrue()
})
test('compare sets', () => {
const toCompareDifferent = new Set([ { a : 1 }, { a : 2 } ])
const toCompareSame = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
const testSet = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ])
expect(equals(toCompareSame, testSet)).toBeTruthy()
expect(equals(toCompareDifferent, testSet)).toBeFalsy()
expect(equalsRamda(toCompareSame, testSet)).toBeTruthy()
expect(equalsRamda(toCompareDifferent, testSet)).toBeFalsy()
})
test('compare simple sets', () => {
const testSet = new Set([ '2', '3', '3', '2', '1' ])
expect(equals(new Set([ '3', '2', '1' ]), testSet)).toBeTruthy()
expect(equals(new Set([ '3', '2', '0' ]), testSet)).toBeFalsy()
})
test('various examples', () => {
expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue()
expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse()
expect(equals(1, 1)).toBeTrue()
expect(equals(1, '1')).toBeFalse()
expect(equals({}, {})).toBeTrue()
expect(equals({
a : 1,
b : 2,
},
{
a : 1,
b : 2,
})).toBeTrue()
expect(equals({
a : 1,
b : 2,
},
{
a : 1,
b : 1,
})).toBeFalse()
expect(equals({
a : 1,
b : false,
},
{
a : 1,
b : 1,
})).toBeFalse()
expect(equals({
a : 1,
b : 2,
},
{
a : 1,
b : 2,
c : 3,
})).toBeFalse()
expect(equals({
x : {
a : 1,
b : 2,
},
},
{
x : {
a : 1,
b : 2,
c : 3,
},
})).toBeFalse()
expect(equals({
a : 1,
b : 2,
},
{
a : 1,
b : 3,
})).toBeFalse()
expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue()
expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse()
expect(equals({ a : {} }, { a : {} })).toBeTrue()
expect(equals('', '')).toBeTrue()
expect(equals('foo', 'foo')).toBeTrue()
expect(equals('foo', 'bar')).toBeFalse()
expect(equals(0, false)).toBeFalse()
expect(equals(/\s/g, null)).toBeFalse()
expect(equals(null, null)).toBeTrue()
expect(equals(false)(null)).toBeFalse()
})
test('with custom functions', () => {
function foo(){
return 1
}
foo.prototype.toString = () => ''
const result = equals(foo, foo)
expect(result).toBeTrue()
})
test('with classes', () => {
class Foo{}
const foo = new Foo()
const result = equals(foo, foo)
expect(result).toBeTrue()
})
test('with negative zero', () => {
expect(equals(-0, -0)).toBeTrue()
expect(equals(-0, 0)).toBeFalse()
expect(equals(0, 0)).toBeTrue()
expect(equals(-0, 1)).toBeFalse()
})
test('with big int', () => {
const a = BigInt(9007199254740991)
const b = BigInt(9007199254740991)
const c = BigInt(7007199254740991)
expect(equals(a, b)).toBeTrue()
expect(equals(a, c)).toBeFalse()
})
describe('brute force', () => {
compareCombinations({
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 0,
"RESULTS_MISMATCH": 8,
"SHOULD_NOT_THROW": 0,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 289,
}
`)
},
firstInput : variousTypes,
fn : equals,
fnRamda : equalsRamda,
secondInput : variousTypes,
})
})
```
TypeScript test
```typescript
import {equals} from 'rambda'
describe('R.equals', () => {
it('happy', () => {
const result = equals(4, 1)
result // $ExpectType boolean
})
it('with object', () => {
const foo = {a: 1}
const bar = {a: 2}
const result = equals(foo, bar)
result // $ExpectType boolean
})
it('curried', () => {
const result = equals(4)(1)
result // $ExpectType boolean
})
})
```
[](#equals)
### evolve
```typescript
evolve(rules: ((x: T) => U)[], list: T[]): U[]
```
It takes object or array of functions as set of rules. These `rules` are applied to the `iterable` input to produce the result.
Try this R.evolve example in Rambda REPL
All TypeScript definitions
```typescript
evolve(rules: ((x: T) => U)[], list: T[]): U[];
evolve(rules: ((x: T) => U)[]) : (list: T[]) => U[];
evolve>(rules: E, obj: V): Evolve;
evolve(rules: E): >(obj: V) => Evolve;
```
R.evolve source
```javascript
import { isArray } from './_internals/isArray.js'
import { mapArray, mapObject } from './map.js'
import { type } from './type.js'
export function evolveArray(rules, list){
return mapArray(
(x, i) => {
if (type(rules[ i ]) === 'Function'){
return rules[ i ](x)
}
return x
},
list,
true
)
}
export function evolveObject(rules, iterable){
return mapObject((x, prop) => {
if (type(x) === 'Object'){
const typeRule = type(rules[ prop ])
if (typeRule === 'Function'){
return rules[ prop ](x)
}
if (typeRule === 'Object'){
return evolve(rules[ prop ], x)
}
return x
}
if (type(rules[ prop ]) === 'Function'){
return rules[ prop ](x)
}
return x
}, iterable)
}
export function evolve(rules, iterable){
if (arguments.length === 1){
return _iterable => evolve(rules, _iterable)
}
const rulesType = type(rules)
const iterableType = type(iterable)
if (iterableType !== rulesType){
throw new Error('iterableType !== rulesType')
}
if (![ 'Object', 'Array' ].includes(rulesType)){
throw new Error(`'iterable' and 'rules' are from wrong type ${ rulesType }`)
}
if (iterableType === 'Object'){
return evolveObject(rules, iterable)
}
return evolveArray(rules, iterable)
}
```
Tests
```javascript
import { evolve as evolveRamda } from 'ramda'
import { add } from '../rambda.js'
import { compareCombinations, compareToRamda } from './_internals/testUtils.js'
import { evolve } from './evolve.js'
test('happy', () => {
const rules = {
foo : add(1),
nested : { bar : x => Object.keys(x).length },
}
const input = {
a : 1,
foo : 2,
nested : { bar : { z : 3 } },
}
const result = evolve(rules, input)
expect(result).toEqual({
a : 1,
foo : 3,
nested : { bar : 1 },
})
})
test('nested rule is wrong', () => {
const rules = {
foo : add(1),
nested : { bar : 10 },
}
const input = {
a : 1,
foo : 2,
nested : { bar : { z : 3 } },
}
const result = evolve(rules)(input)
expect(result).toEqual({
a : 1,
foo : 3,
nested : { bar : { z : 3 } },
})
})
test('is recursive', () => {
const rules = {
nested : {
second : add(-1),
third : add(1),
},
}
const object = {
first : 1,
nested : {
second : 2,
third : 3,
},
}
const expected = {
first : 1,
nested : {
second : 1,
third : 4,
},
}
const result = evolve(rules, object)
expect(result).toEqual(expected)
})
test('ignores primitive values', () => {
const rules = {
n : 2,
m : 'foo',
}
const object = {
n : 0,
m : 1,
}
const expected = {
n : 0,
m : 1,
}
const result = evolve(rules, object)
expect(result).toEqual(expected)
})
test('with array', () => {
const rules = [ add(1), add(-1) ]
const list = [ 100, 1400 ]
const expected = [ 101, 1399 ]
const result = evolve(rules, list)
expect(result).toEqual(expected)
})
const rulesObject = { a : add(1) }
const rulesList = [ add(1) ]
const possibleIterables = [ null, undefined, '', 42, [], [ 1 ], { a : 1 } ]
const possibleRules = [ ...possibleIterables, rulesList, rulesObject ]
describe('brute force', () => {
compareCombinations({
firstInput : possibleRules,
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 4,
"RESULTS_MISMATCH": 0,
"SHOULD_NOT_THROW": 51,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 63,
}
`)
},
secondInput : possibleIterables,
fn : evolve,
fnRamda : evolveRamda,
})
})
```
TypeScript test
```typescript
import {evolve, add} from 'rambda'
describe('R.evolve', () => {
it('happy', () => {
const input = {
foo: 2,
nested: {
a: 1,
bar: 3,
},
}
const rules = {
foo: add(1),
nested: {
a: add(-1),
bar: add(1),
},
}
const result = evolve(rules, input)
const curriedResult = evolve(rules)(input)
result.nested.a // $ExpectType number
curriedResult.nested.a // $ExpectType number
result.nested.bar // $ExpectType number
result.foo // $ExpectType number
})
it('with array', () => {
const rules = [String, String]
const input = [100, 1400]
const result = evolve(rules, input)
const curriedResult = evolve(rules)(input)
result // $ExpectType string[]
curriedResult // $ExpectType string[]
})
})
```
[](#evolve)
### F
```typescript
F(): boolean
```
Try this R.F example in Rambda REPL
All TypeScript definitions
```typescript
F(): boolean;
```
R.F source
```javascript
export function F(){
return false
}
```
[](#F)
### filter
```typescript
filter(predicate: Predicate): (input: T[]) => T[]
```
It filters list or object `input` using a `predicate` function.
Try this R.filter example in Rambda REPL
All TypeScript definitions
```typescript
filter(predicate: Predicate): (input: T[]) => T[];
filter(predicate: Predicate, input: T[]): T[];
filter(predicate: ObjectPredicate): (x: Dictionary) => Dictionary;
filter(predicate: ObjectPredicate, x: Dictionary): Dictionary;
```
R.filter source
```javascript
import { isArray } from './_internals/isArray.js'
export function filterObject(predicate, obj){
const willReturn = {}
for (const prop in obj){
if (predicate(
obj[ prop ], prop, obj
)){
willReturn[ prop ] = obj[ prop ]
}
}
return willReturn
}
export function filterArray(
predicate, list, indexed = false
){
let index = 0
const len = list.length
const willReturn = []
while (index < len){
const predicateResult = indexed ?
predicate(list[ index ], index) :
predicate(list[ index ])
if (predicateResult){
willReturn.push(list[ index ])
}
index++
}
return willReturn
}
export function filter(predicate, iterable){
if (arguments.length === 1)
return _iterable => filter(predicate, _iterable)
if (!iterable){
throw new Error('Incorrect iterable input')
}
if (isArray(iterable)) return filterArray(
predicate, iterable, false
)
return filterObject(predicate, iterable)
}
```
Tests
```javascript
import { filter as filterRamda } from 'ramda'
import { filter } from './filter.js'
import { T } from './T.js'
const sampleObject = {
a : 1,
b : 2,
c : 3,
d : 4,
}
test('happy', () => {
const isEven = n => n % 2 === 0
expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
expect(filter(isEven, {
a : 1,
b : 2,
d : 3,
})).toEqual({ b : 2 })
})
test('predicate when input is object', () => {
const obj = {
a : 1,
b : 2,
}
const predicate = (
val, prop, inputObject
) => {
expect(inputObject).toEqual(obj)
expect(typeof prop).toBe('string')
return val < 2
}
expect(filter(predicate, obj)).toEqual({ a : 1 })
})
test('with object', () => {
const isEven = n => n % 2 === 0
const result = filter(isEven, sampleObject)
const expectedResult = {
b : 2,
d : 4,
}
expect(result).toEqual(expectedResult)
})
test('bad inputs difference between Ramda and Rambda', () => {
expect(() => filter(T, null)).toThrowWithMessage(Error,
'Incorrect iterable input')
expect(() => filter(T)(undefined)).toThrowWithMessage(Error,
'Incorrect iterable input')
expect(() => filterRamda(T, null)).toThrowWithMessage(TypeError,
'Cannot read properties of null (reading \'fantasy-land/filter\')')
expect(() => filterRamda(T, undefined)).toThrowWithMessage(TypeError,
'Cannot read properties of undefined (reading \'fantasy-land/filter\')')
})
```
TypeScript test
```typescript
import {filter} from 'rambda'
const list = [1, 2, 3]
const obj = {a: 1, b: 2}
describe('R.filter with array', () => {
it('happy', () => {
const result = filter(x => {
x // $ExpectType number
return x > 1
}, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = filter(x => {
x // $ExpectType number
return x > 1
})(list)
result // $ExpectType number[]
})
})
describe('R.filter with objects', () => {
it('happy', () => {
const result = filter((val, prop, origin) => {
val // $ExpectType number
prop // $ExpectType string
origin // $ExpectType Dictionary
return val > 1
}, obj)
result // $ExpectType Dictionary
})
it('curried version requires second dummy type', () => {
const result = filter((val, prop, origin) => {
val // $ExpectType number
prop // $ExpectType string
origin // $ExpectType Dictionary
return val > 1
})(obj)
result // $ExpectType Dictionary
})
})
```
[](#filter)
### find
```typescript
find(predicate: (x: T) => boolean, list: T[]): T | undefined
```
It returns the first element of `list` that satisfy the `predicate`.
If there is no such element, it returns `undefined`.
Try this R.find example in Rambda REPL
All TypeScript definitions
```typescript
find(predicate: (x: T) => boolean, list: T[]): T | undefined;
find(predicate: (x: T) => boolean): (list: T[]) => T | undefined;
```
R.find source
```javascript
export function find(predicate, list){
if (arguments.length === 1) return _list => find(predicate, _list)
let index = 0
const len = list.length
while (index < len){
const x = list[ index ]
if (predicate(x)){
return x
}
index++
}
}
```
Tests
```javascript
import { find } from './find.js'
import { propEq } from './propEq.js'
const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
test('happy', () => {
const fn = propEq(2, 'a')
expect(find(fn, list)).toEqual({ a : 2 })
})
test('with curry', () => {
const fn = propEq(4, 'a')
expect(find(fn)(list)).toBeUndefined()
})
test('with empty list', () => {
expect(find(() => true, [])).toBeUndefined()
})
```
TypeScript test
```typescript
import {find} from 'rambda'
const list = [1, 2, 3]
describe('R.find', () => {
it('happy', () => {
const predicate = (x: number) => x > 2
const result = find(predicate, list)
result // $ExpectType number | undefined
})
it('curried', () => {
const predicate = (x: number) => x > 2
const result = find(predicate)(list)
result // $ExpectType number | undefined
})
})
```
[](#find)
### findIndex
```typescript
findIndex(predicate: (x: T) => boolean, list: T[]): number
```
It returns the index of the first element of `list` satisfying the `predicate` function.
If there is no such element, then `-1` is returned.
Try this R.findIndex example in Rambda REPL
All TypeScript definitions
```typescript
findIndex(predicate: (x: T) => boolean, list: T[]): number;
findIndex(predicate: (x: T) => boolean): (list: T[]) => number;
```
R.findIndex source
```javascript
export function findIndex(predicate, list){
if (arguments.length === 1) return _list => findIndex(predicate, _list)
const len = list.length
let index = -1
while (++index < len){
if (predicate(list[ index ])){
return index
}
}
return -1
}
```
Tests
```javascript
import { findIndex } from './findIndex.js'
import { propEq } from './propEq.js'
const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
test('happy', () => {
expect(findIndex(propEq(2, 'a'), list)).toBe(1)
expect(findIndex(propEq(1, 'a'))(list)).toBe(0)
expect(findIndex(propEq(4, 'a'))(list)).toBe(-1)
})
```
TypeScript test
```typescript
import {findIndex} from 'rambda'
const list = [1, 2, 3]
describe('R.findIndex', () => {
it('happy', () => {
const predicate = (x: number) => x > 2
const result = findIndex(predicate, list)
result // $ExpectType number
})
it('curried', () => {
const predicate = (x: number) => x > 2
const result = findIndex(predicate)(list)
result // $ExpectType number
})
})
```
[](#findIndex)
### findLast
```typescript
findLast(fn: (x: T) => boolean, list: T[]): T | undefined
```
It returns the last element of `list` satisfying the `predicate` function.
If there is no such element, then `undefined` is returned.
Try this R.findLast example in Rambda REPL
All TypeScript definitions
```typescript
findLast(fn: (x: T) => boolean, list: T[]): T | undefined;
findLast(fn: (x: T) => boolean): (list: T[]) => T | undefined;
```
R.findLast source
```javascript
export function findLast(predicate, list){
if (arguments.length === 1) return _list => findLast(predicate, _list)
let index = list.length
while (--index >= 0){
if (predicate(list[ index ])){
return list[ index ]
}
}
return undefined
}
```
Tests
```javascript
import { findLast } from './findLast.js'
test('happy', () => {
const result = findLast(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])
expect(result).toBe(4)
expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})
test('with curry', () => {
expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(4)
})
const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
return x % 2 === 0
}
const gt100 = function (x){
return x > 100
}
const isStr = function (x){
return typeof x === 'string'
}
const xGt100 = function (o){
return o && o.x > 100
}
test('ramda 1', () => {
expect(findLast(even, a)).toBe(0)
expect(findLast(gt100, a)).toBe(300)
expect(findLast(isStr, a)).toBe('cow')
expect(findLast(xGt100, a)).toEqual(obj2)
})
test('ramda 2', () => {
expect(findLast(even, [ 'zing' ])).toBeUndefined()
})
test('ramda 3', () => {
expect(findLast(even, [ 2, 3, 5 ])).toBe(2)
})
test('ramda 4', () => {
expect(findLast(even, [])).toBeUndefined()
})
```
TypeScript test
```typescript
import {findLast} from 'rambda'
const list = [1, 2, 3]
describe('R.findLast', () => {
it('happy', () => {
const predicate = (x: number) => x > 2
const result = findLast(predicate, list)
result // $ExpectType number | undefined
})
it('curried', () => {
const predicate = (x: number) => x > 2
const result = findLast(predicate)(list)
result // $ExpectType number | undefined
})
})
```
[](#findLast)
### findLastIndex
```typescript
findLastIndex(predicate: (x: T) => boolean, list: T[]): number
```
It returns the index of the last element of `list` satisfying the `predicate` function.
If there is no such element, then `-1` is returned.
Try this R.findLastIndex example in Rambda REPL
All TypeScript definitions
```typescript
findLastIndex(predicate: (x: T) => boolean, list: T[]): number;
findLastIndex(predicate: (x: T) => boolean): (list: T[]) => number;
```
R.findLastIndex source
```javascript
export function findLastIndex(fn, list){
if (arguments.length === 1) return _list => findLastIndex(fn, _list)
let index = list.length
while (--index >= 0){
if (fn(list[ index ])){
return index
}
}
return -1
}
```
Tests
```javascript
import { findLastIndex } from './findLastIndex.js'
test('happy', () => {
const result = findLastIndex(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ])
expect(result).toBe(5)
expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)
})
test('with curry', () => {
expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(5)
})
const obj1 = { x : 100 }
const obj2 = { x : 200 }
const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]
const even = function (x){
return x % 2 === 0
}
const gt100 = function (x){
return x > 100
}
const isStr = function (x){
return typeof x === 'string'
}
const xGt100 = function (o){
return o && o.x > 100
}
test('ramda 1', () => {
expect(findLastIndex(even, a)).toBe(15)
expect(findLastIndex(gt100, a)).toBe(9)
expect(findLastIndex(isStr, a)).toBe(3)
expect(findLastIndex(xGt100, a)).toBe(10)
})
test('ramda 2', () => {
expect(findLastIndex(even, [ 'zing' ])).toBe(-1)
})
test('ramda 3', () => {
expect(findLastIndex(even, [ 2, 3, 5 ])).toBe(0)
})
test('ramda 4', () => {
expect(findLastIndex(even, [])).toBe(-1)
})
```
TypeScript test
```typescript
import {findLastIndex} from 'rambda'
const list = [1, 2, 3]
describe('R.findLastIndex', () => {
it('happy', () => {
const predicate = (x: number) => x > 2
const result = findLastIndex(predicate, list)
result // $ExpectType number
})
it('curried', () => {
const predicate = (x: number) => x > 2
const result = findLastIndex(predicate)(list)
result // $ExpectType number
})
})
```
[](#findLastIndex)
### flatten
```typescript
flatten(list: any[]): T[]
```
It deeply flattens an array.
Try this R.flatten example in Rambda REPL
All TypeScript definitions
```typescript
flatten(list: any[]): T[];
```
R.flatten source
```javascript
import { isArray } from './_internals/isArray.js'
export function flatten(list, input){
const willReturn = input === undefined ? [] : input
for (let i = 0; i < list.length; i++){
if (isArray(list[ i ])){
flatten(list[ i ], willReturn)
} else {
willReturn.push(list[ i ])
}
}
return willReturn
}
```
Tests
```javascript
import { flatten } from './flatten.js'
test('happy', () => {
expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ])
expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])
expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ])
expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])
})
test('readme example', () => {
const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ])
expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])
})
```
TypeScript test
```typescript
import {flatten} from 'rambda'
describe('flatten', () => {
it('happy', () => {
const result = flatten([1, 2, [3, [4]]])
result // $ExpectType number[]
})
})
```
[](#flatten)
### flip
It returns function which calls `fn` with exchanged first and second argument.
Try this R.flip example in Rambda REPL
[](#flip)
### forEach
```typescript
forEach(fn: Iterator, list: T[]): T[]
```
It applies `iterable` function over all members of `list` and returns `list`.
Try this R.forEach example in Rambda REPL
All TypeScript definitions
```typescript
forEach(fn: Iterator, list: T[]): T[];
forEach(fn: Iterator): (list: T[]) => T[];
forEach(fn: ObjectIterator, list: Dictionary): Dictionary;
forEach(fn: ObjectIterator): (list: Dictionary) => Dictionary;
```
R.forEach source
```javascript
import { isArray } from './_internals/isArray.js'
import { forEachObjIndexedFn } from './forEachObjIndexed.js'
export function forEach(fn, iterable){
if (arguments.length === 1) return _list => forEach(fn, _list)
if (iterable === undefined) return
if (isArray(iterable)){
let index = 0
const len = iterable.length
while (index < len){
fn(iterable[ index ])
index++
}
} else return forEachObjIndexedFn(fn, iterable)
return iterable
}
```
Tests
```javascript
import { forEach } from './forEach.js'
import { type } from './type.js'
test('happy', () => {
const sideEffect = {}
forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ])
expect(sideEffect).toEqual({
foo1 : 11,
foo2 : 12,
})
})
test('iterate over object', () => {
const obj = {
a : 1,
b : [ 1, 2 ],
c : { d : 7 },
f : 'foo',
}
const result = {}
const returned = forEach((
val, prop, inputObj
) => {
expect(type(inputObj)).toBe('Object')
result[ prop ] = `${ prop }-${ type(val) }`
})(obj)
const expected = {
a : 'a-Number',
b : 'b-Array',
c : 'c-Object',
f : 'f-String',
}
expect(result).toEqual(expected)
expect(returned).toEqual(obj)
})
test('with empty list', () => {
const list = []
const result = forEach(x => x * x)(list)
expect(result).toEqual(list)
})
test('with wrong input', () => {
const list = undefined
const result = forEach(x => x * x)(list)
expect(result).toBeUndefined()
})
test('returns the input', () => {
const list = [ 1, 2, 3 ]
const result = forEach(x => x * x)(list)
expect(result).toEqual(list)
})
```
TypeScript test
```typescript
import {forEach} from 'rambda'
const list = [1, 2, 3]
const obj = {a: 1, b: 2}
describe('R.forEach with arrays', () => {
it('happy', () => {
const result = forEach(a => {
a // $ExpectType number
}, list)
result // $ExpectType number[]
})
it('curried require an explicit typing', () => {
const result = forEach(a => {
a // $ExpectType number
})(list)
result // $ExpectType number[]
})
})
describe('R.forEach with objects', () => {
it('happy', () => {
const result = forEach((a, b, c) => {
a // $ExpectType number
b // $ExpectType string
c // $ExpectType Dictionary
return `${a}`
}, obj)
result // $ExpectType Dictionary
})
it('curried require an input typing and a dummy third typing', () => {
// Required in order all typings to work
const result = forEach((a, b, c) => {
a // $ExpectType number
b // $ExpectType string
c // $ExpectType Dictionary
})(obj)
result // $ExpectType Dictionary
})
it('iterator without property', () => {
const result = forEach(a => {
a // $ExpectType number
}, obj)
result // $ExpectType Dictionary
})
})
```
[](#forEach)
### forEachObjIndexed
[](#forEachObjIndexed)
### fromPairs
It transforms a `listOfPairs` to an object.
Try this R.fromPairs example in Rambda REPL
[](#fromPairs)
### groupBy
It splits `list` according to a provided `groupFn` function and returns an object.
Try this R.groupBy example in Rambda REPL
[](#groupBy)
### groupWith
It returns separated version of list or string `input`, where separation is done with equality `compareFn` function.
Try this R.groupWith example in Rambda REPL
[](#groupWith)
### gt
Try this R.gt example in Rambda REPL
[](#gt)
### gte
Try this R.gte example in Rambda REPL
[](#gte)
### has
```typescript
has(prop: string, obj: T): boolean
```
It returns `true` if `obj` has property `prop`.
Try this R.has example in Rambda REPL
All TypeScript definitions
```typescript
has(prop: string, obj: T): boolean;
has(prop: string): (obj: T) => boolean;
```
R.has source
```javascript
export function has(prop, obj){
if (arguments.length === 1) return _obj => has(prop, _obj)
if (!obj) return false
return obj.hasOwnProperty(prop)
}
```
Tests
```javascript
import { has } from './has.js'
test('happy', () => {
expect(has('a')({ a : 1 })).toBeTrue()
expect(has('b', { a : 1 })).toBeFalse()
})
test('with non-object', () => {
expect(has('a', undefined)).toBeFalse()
expect(has('a', null)).toBeFalse()
expect(has('a', true)).toBeFalse()
expect(has('a', '')).toBeFalse()
expect(has('a', /a/)).toBeFalse()
})
```
TypeScript test
```typescript
import {has} from 'rambda'
describe('R.has', () => {
it('happy', () => {
const result = has('foo', {a: 1})
const curriedResult = has('bar')({a: 1})
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
})
```
[](#has)
### hasIn
Try this R.hasIn example in Rambda REPL
[](#hasIn)
### hasPath
```typescript
hasPath(
path: string | string[],
input: object
): boolean
```
It will return true, if `input` object has truthy `path`(calculated with `R.path`).
Try this R.hasPath example in Rambda REPL
All TypeScript definitions
```typescript
hasPath(
path: string | string[],
input: object
): boolean;
hasPath(
path: string | string[]
): (input: object) => boolean;
```
R.hasPath source
```javascript
import { path } from './path.js'
export function hasPath(pathInput, obj){
if (arguments.length === 1){
return objHolder => hasPath(pathInput, objHolder)
}
return path(pathInput, obj) !== undefined
}
```
Tests
```javascript
import { hasPath } from './hasPath.js'
test('when true', () => {
const path = 'a.b'
const obj = { a : { b : [] } }
const result = hasPath(path)(obj)
const expectedResult = true
expect(result).toEqual(expectedResult)
})
test('when false', () => {
const path = 'a.b'
const obj = {}
const result = hasPath(path, obj)
const expectedResult = false
expect(result).toEqual(expectedResult)
})
```
TypeScript test
```typescript
import {hasPath} from 'rambda'
describe('R.hasPath', () => {
it('string path', () => {
const obj = {a: {b: 1}}
const result = hasPath('a.b', obj)
const curriedResult = hasPath('a.c')(obj)
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
it('array path', () => {
const obj = {a: {b: 1}}
const result = hasPath(['a', 'b'], obj)
const curriedResult = hasPath(['a', 'c'])(obj)
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
})
```
[](#hasPath)
### head
```typescript
head(str: string): string
```
It returns the first element of list or string `input`.
Try this R.head example in Rambda REPL
All TypeScript definitions
```typescript
head(str: string): string;
head(str: ''): undefined;
head(list: never[]): undefined;
head(array: T): FirstArrayElement
head(array: T): FirstArrayElement
```
R.head source
```javascript
export function head(listOrString){
if (typeof listOrString === 'string') return listOrString[ 0 ] || ''
return listOrString[ 0 ]
}
```
Tests
```javascript
import { head } from './head.js'
test('head', () => {
expect(head([ 'fi', 'fo', 'fum' ])).toBe('fi')
expect(head([])).toBeUndefined()
expect(head('foo')).toBe('f')
expect(head('')).toBe('')
})
```
TypeScript test
```typescript
import {
emptyList,
emptyString,
mixedList,
mixedListConst,
numberList,
numberListConst,
string,
} from '_internals/typescriptTestUtils'
import {head, last} from 'rambda'
describe('R.head', () => {
it('string', () => {
head(string) // $ExpectType string
last(string) // $ExpectType string
})
it('empty string', () => {
head(emptyString) // $ExpectType undefined
last(emptyString) // $ExpectType undefined
})
it('array', () => {
head(numberList) // $ExpectType number
head(numberListConst) // $ExpectType 1
last(numberList) // $ExpectType number
last(numberListConst) // $ExpectType 3
})
it('empty array', () => {
const list = [] as const
head(emptyList) // $ExpectType undefined
head(list) // $ExpectType never
last(emptyList) // $ExpectType undefined
last(list) // $ExpectType never
})
it('mixed', () => {
head(mixedList) // $ExpectType string | number
head(mixedListConst) // $ExpectType 1
last(mixedList) // $ExpectType string | number
last(mixedListConst) // $ExpectType "bar"
})
})
```
[](#head)
### identical
It returns `true` if its arguments `a` and `b` are identical.
Otherwise, it returns `false`.
Try this R.identical example in Rambda REPL
[](#identical)
### identity
```typescript
identity(input: T): T
```
It just passes back the supplied `input` argument.
Try this R.identity example in Rambda REPL
All TypeScript definitions
```typescript
identity(input: T): T;
```
R.identity source
```javascript
export function identity(x){
return x
}
```
Tests
```javascript
import { identity } from './identity.js'
test('happy', () => {
expect(identity(7)).toBe(7)
expect(identity(true)).toBeTrue()
expect(identity({ a : 1 })).toEqual({ a : 1 })
})
```
TypeScript test
```typescript
import {identity} from 'rambda'
describe('R.identity', () => {
it('happy', () => {
const result = identity(4)
result // $ExpectType 4
})
})
```
[](#identity)
### ifElse
```typescript
ifElse(
pred: (a: T) => a is TFiltered,
onTrue: (a: TFiltered) => TOnTrueResult,
onFalse: (a: Exclude) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult
```
It expects `condition`, `onTrue` and `onFalse` functions as inputs and it returns a new function with example name of `fn`.
When `fn`` is called with `input` argument, it will return either `onTrue(input)` or `onFalse(input)` depending on `condition(input)` evaluation.
Try this R.ifElse example in Rambda REPL
All TypeScript definitions
```typescript
ifElse(
pred: (a: T) => a is TFiltered,
onTrue: (a: TFiltered) => TOnTrueResult,
onFalse: (a: Exclude) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult;
ifElse(fn: (...args: TArgs) => boolean, onTrue: (...args: TArgs) => TOnTrueResult, onFalse: (...args: TArgs) => TOnFalseResult): (...args: TArgs) => TOnTrueResult | TOnFalseResult;
```
R.ifElse source
```javascript
import { curry } from './curry.js'
function ifElseFn(
condition, onTrue, onFalse
){
return (...input) => {
const conditionResult =
typeof condition === 'boolean' ? condition : condition(...input)
if (conditionResult === true){
return onTrue(...input)
}
return onFalse(...input)
}
}
export const ifElse = curry(ifElseFn)
```
Tests
```javascript
import { always } from './always.js'
import { has } from './has.js'
import { identity } from './identity.js'
import { ifElse } from './ifElse.js'
import { prop } from './prop.js'
const condition = has('foo')
const v = function (a){
return typeof a === 'number'
}
const t = function (a){
return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false
test('happy', () => {
const fn = ifElse(condition, ifFn)(elseFn)
expect(fn({ foo : 'bar' })).toBe(3)
expect(fn({ fo : 'bar' })).toBeFalse()
})
test('ramda spec', () => {
const ifIsNumber = ifElse(v)
expect(ifIsNumber(t, identity)(15)).toBe(16)
expect(ifIsNumber(t, identity)('hello')).toBe('hello')
})
test('pass all arguments', () => {
const identity = function (a){
return a
}
const v = function (){
return true
}
const onTrue = function (a, b){
expect(a).toBe(123)
expect(b).toBe('abc')
}
ifElse(
v, onTrue, identity
)(123, 'abc')
})
test('accept constant as condition', () => {
const fn = ifElse(true)(always(true))(always(false))
expect(fn()).toBeTrue()
})
test('accept constant as condition - case 2', () => {
const fn = ifElse(
false, always(true), always(false)
)
expect(fn()).toBeFalse()
})
test('curry 1', () => {
const fn = ifElse(condition, ifFn)(elseFn)
expect(fn({ foo : 'bar' })).toBe(3)
expect(fn({ fo : 'bar' })).toBeFalse()
})
test('curry 2', () => {
const fn = ifElse(condition)(ifFn)(elseFn)
expect(fn({ foo : 'bar' })).toBe(3)
expect(fn({ fo : 'bar' })).toBeFalse()
})
test('simple arity of 1', () => {
const condition = x => x > 5
const onTrue = x => x + 1
const onFalse = x => x + 10
const result = ifElse(
condition, onTrue, onFalse
)(1)
expect(result).toBe(11)
})
test('simple arity of 2', () => {
const condition = (x, y) => x + y > 5
const onTrue = (x, y) => x + y + 1
const onFalse = (x, y) => x + y + 10
const result = ifElse(
condition, onTrue, onFalse
)(1, 10)
expect(result).toBe(12)
})
```
TypeScript test
```typescript
import {ifElse} from 'rambda'
describe('R.ifElse', () => {
it('happy', () => {
const condition = (x: number) => x > 5
const onTrue = (x: number) => `foo${x}`
const onFalse = (x: number) => `bar${x}`
const fn = ifElse(condition, onTrue, onFalse)
fn // $ExpectType (x: number) => string
const result = fn(3)
result // $ExpectType string
})
it('arity of 2', () => {
const condition = (x: number, y: string) => x + y.length > 5
const onTrue = (x: number, y: string) => `foo${x}-${y}`
const onFalse = (x: number, y: string) => `bar${x}-${y}`
const fn = ifElse(condition, onTrue, onFalse)
fn // $ExpectType (x: number, y: string) => string
const result = fn(3, 'hello')
result // $ExpectType string
})
test('DefinitelyTyped#59291', () => {
const getLengthIfStringElseDouble = ifElse(
(a: string | number): a is string => true,
a => a.length,
a => a * 2
)
getLengthIfStringElseDouble('foo') // $ExpectType number
getLengthIfStringElseDouble(3) // $ExpectType number
const result = ifElse(
(a: {
foo?: string,
bar: number | string,
}): a is {foo: string, bar: string} => true,
(a): [string, string] => [a.foo, a.bar],
(a): [string | undefined, string | number] => [a.foo, a.bar]
)
result // $ExpectType (a: { foo?: string | undefined; bar: string | number; }) => [string, string] | [string | undefined, string | number]
})
})
```
[](#ifElse)
### inc
It increments a number.
Try this R.inc example in Rambda REPL
[](#inc)
### includes
```typescript
includes(valueToFind: T, input: string): boolean
```
If `input` is string, then this method work as native `String.includes`.
If `input` is array, then `R.equals` is used to define if `valueToFind` belongs to the list.
Try this R.includes example in Rambda REPL
All TypeScript definitions
```typescript
includes(valueToFind: T, input: string): boolean;
includes(valueToFind: T): (input: string) => boolean;
includes(valueToFind: T, input: T[]): boolean;
includes(valueToFind: T): (input: T[]) => boolean;
```
R.includes source
```javascript
import { isArray } from './_internals/isArray.js'
import { _indexOf } from './equals.js'
export function includes(valueToFind, iterable){
if (arguments.length === 1)
return _iterable => includes(valueToFind, _iterable)
if (typeof iterable === 'string'){
return iterable.includes(valueToFind)
}
if (!iterable){
throw new TypeError(`Cannot read property \'indexOf\' of ${ iterable }`)
}
if (!isArray(iterable)) return false
return _indexOf(valueToFind, iterable) > -1
}
```
Tests
```javascript
import { includes as includesRamda } from 'ramda'
import { includes } from './includes.js'
test('with string as iterable', () => {
const str = 'foo bar'
expect(includes('bar')(str)).toBeTrue()
expect(includesRamda('bar')(str)).toBeTrue()
expect(includes('never', str)).toBeFalse()
expect(includesRamda('never', str)).toBeFalse()
})
test('with array as iterable', () => {
const arr = [ 1, 2, 3 ]
expect(includes(2)(arr)).toBeTrue()
expect(includesRamda(2)(arr)).toBeTrue()
expect(includes(4, arr)).toBeFalse()
expect(includesRamda(4, arr)).toBeFalse()
})
test('with list of objects as iterable', () => {
const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]
expect(includes({ c : 3 }, arr)).toBeTrue()
expect(includesRamda({ c : 3 }, arr)).toBeTrue()
})
test('with NaN', () => {
const result = includes(NaN, [ NaN ])
const ramdaResult = includesRamda(NaN, [ NaN ])
expect(result).toBeTrue()
expect(ramdaResult).toBeTrue()
})
test('with wrong input that does not throw', () => {
const result = includes(1, /foo/g)
const ramdaResult = includesRamda(1, /foo/g)
expect(result).toBeFalse()
expect(ramdaResult).toBeFalse()
})
test('throws on wrong input - match ramda behaviour', () => {
expect(() => includes(2, null)).toThrowWithMessage(TypeError,
'Cannot read property \'indexOf\' of null')
expect(() => includesRamda(2, null)).toThrowWithMessage(TypeError,
'Cannot read properties of null (reading \'indexOf\')')
expect(() => includes(2, undefined)).toThrowWithMessage(TypeError,
'Cannot read property \'indexOf\' of undefined')
expect(() => includesRamda(2, undefined)).toThrowWithMessage(TypeError,
'Cannot read properties of undefined (reading \'indexOf\')')
})
```
TypeScript test
```typescript
import {includes} from 'rambda'
const list = [{a: {b: '1'}}, {a: {c: '2'}}, {a: {b: '3'}}]
describe('R.includes', () => {
it('happy', () => {
const result = includes({a: {b: '1'}}, list)
result // $ExpectType boolean
const result2 = includes('oo', ['f', 'oo'])
result2 // $ExpectType boolean
})
it('with string', () => {
const str = 'foo' as 'foo' | 'bar'
const result = includes('oo', str)
const curriedResult = includes('oo')(str)
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
})
```
[](#includes)
### indexBy
It generates object with properties provided by `condition` and values provided by `list` array.
If `condition` is a function, then all list members are passed through it.
If `condition` is a string, then all list members are passed through `R.path(condition)`.
Try this R.indexBy example in Rambda REPL
[](#indexBy)
### indexOf
It returns the index of the first element of `list` equals to `valueToFind`.
If there is no such element, it returns `-1`.
Try this R.indexOf example in Rambda REPL
[](#indexOf)
### init
```typescript
init(input: T): T extends readonly [...infer U, any] ? U : [...T]
```
It returns all but the last element of list or string `input`.
Try this R.init example in Rambda REPL
All TypeScript definitions
```typescript
init(input: T): T extends readonly [...infer U, any] ? U : [...T];
init(input: string): string;
```
R.init source
```javascript
import baseSlice from './_internals/baseSlice.js'
export function init(listOrString){
if (typeof listOrString === 'string') return listOrString.slice(0, -1)
return listOrString.length ?
baseSlice(
listOrString, 0, -1
) :
[]
}
```
Tests
```javascript
import { init } from './init.js'
test('with array', () => {
expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ])
expect(init([ 1, 2 ])).toEqual([ 1 ])
expect(init([ 1 ])).toEqual([])
expect(init([])).toEqual([])
expect(init([])).toEqual([])
expect(init([ 1 ])).toEqual([])
})
test('with string', () => {
expect(init('foo')).toBe('fo')
expect(init('f')).toBe('')
expect(init('')).toBe('')
})
```
TypeScript test
```typescript
import {init} from 'rambda'
describe('R.init', () => {
it('with string', () => {
const result = init('foo')
result // $ExpectType string
})
it('with list - one type', () => {
const result = init([1, 2, 3])
result // $ExpectType number[]
})
it('with list - mixed types', () => {
const result = init([1, 2, 3, 'foo', 'bar'])
result // $ExpectType (string | number)[]
})
})
```
[](#init)
### innerJoin
It returns a new list by applying a `predicate` function to all elements of `list1` and `list2` and keeping only these elements where `predicate` returns `true`.
Try this R.innerJoin example in Rambda REPL
[](#innerJoin)
### intersection
It loops through `listA` and `listB` and returns the intersection of the two according to `R.equals`.
Try this R.intersection example in Rambda REPL
[](#intersection)
### intersperse
It adds a `separator` between members of `list`.
Try this R.intersperse example in Rambda REPL
[](#intersperse)
### is
It returns `true` if `x` is instance of `targetPrototype`.
Try this R.is example in Rambda REPL
[](#is)
### isEmpty
```typescript
isEmpty(x: T): boolean
```
It returns `true` if `x` is `empty`.
Try this R.isEmpty example in Rambda REPL
All TypeScript definitions
```typescript
isEmpty(x: T): boolean;
```
R.isEmpty source
```javascript
import { type } from './type.js'
export function isEmpty(input){
const inputType = type(input)
if ([ 'Undefined', 'NaN', 'Number', 'Null' ].includes(inputType))
return false
if (!input) return true
if (inputType === 'Object'){
return Object.keys(input).length === 0
}
if (inputType === 'Array'){
return input.length === 0
}
return false
}
```
Tests
```javascript
import { isEmpty } from './isEmpty.js'
test('happy', () => {
expect(isEmpty(undefined)).toBeFalse()
expect(isEmpty('')).toBeTrue()
expect(isEmpty(null)).toBeFalse()
expect(isEmpty(' ')).toBeFalse()
expect(isEmpty(new RegExp(''))).toBeFalse()
expect(isEmpty([])).toBeTrue()
expect(isEmpty([ [] ])).toBeFalse()
expect(isEmpty({})).toBeTrue()
expect(isEmpty({ x : 0 })).toBeFalse()
expect(isEmpty(0)).toBeFalse()
expect(isEmpty(NaN)).toBeFalse()
expect(isEmpty([ '' ])).toBeFalse()
})
```
TypeScript test
```typescript
import {isEmpty} from 'rambda'
describe('R.isEmpty', () => {
it('happy', () => {
const result = isEmpty('foo')
result // $ExpectType boolean
})
})
```
[](#isEmpty)
### isNil
```typescript
isNil(x: any): x is null | undefined
```
It returns `true` if `x` is either `null` or `undefined`.
Try this R.isNil example in Rambda REPL
All TypeScript definitions
```typescript
isNil(x: any): x is null | undefined;
```
R.isNil source
```javascript
export function isNil(x){
return x === undefined || x === null
}
```
Tests
```javascript
import { isNil } from './isNil.js'
test('happy', () => {
expect(isNil(null)).toBeTrue()
expect(isNil(undefined)).toBeTrue()
expect(isNil([])).toBeFalse()
})
```
[](#isNil)
### join
```typescript
join(glue: string, list: T[]): string
```
It returns a string of all `list` instances joined with a `glue`.
Try this R.join example in Rambda REPL
All TypeScript definitions
```typescript
join(glue: string, list: T[]): string;
join(glue: string): (list: T[]) => string;
```
R.join source
```javascript
export function join(glue, list){
if (arguments.length === 1) return _list => join(glue, _list)
return list.join(glue)
}
```
Tests
```javascript
import { join } from './join.js'
test('curry', () => {
expect(join('|')([ 'foo', 'bar', 'baz' ])).toBe('foo|bar|baz')
expect(join('|', [ 1, 2, 3 ])).toBe('1|2|3')
const spacer = join(' ')
expect(spacer([ 'a', 2, 3.4 ])).toBe('a 2 3.4')
})
```
TypeScript test
```typescript
import {join} from 'rambda'
describe('R.join', () => {
it('happy', () => {
const result = join('|', [1, 2, 3])
result // $ExpectType string
})
})
```
[](#join)
### juxt
```typescript
juxt(fns: [(...a: A) => R1]): (...a: A) => [R1]
```
It applies list of function to a list of inputs.
Try this R.juxt example in Rambda REPL
All TypeScript definitions
```typescript
juxt(fns: [(...a: A) => R1]): (...a: A) => [R1];
juxt(fns: [(...a: A) => R1, (...a: A) => R2]): (...a: A) => [R1, R2];
juxt(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3]): (...a: A) => [R1, R2, R3];
juxt(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3, (...a: A) => R4]): (...a: A) => [R1, R2, R3, R4];
juxt(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3, (...a: A) => R4, (...a: A) => R5]): (...a: A) => [R1, R2, R3, R4, R5];
juxt(fns: Array<(...args: A) => U>): (...args: A) => U[];
```
R.juxt source
```javascript
export function juxt(listOfFunctions){
return (...args) => listOfFunctions.map(fn => fn(...args))
}
```
Tests
```javascript
import { juxt } from './juxt.js'
test('happy', () => {
const fn = juxt([ Math.min, Math.max, Math.min ])
const result = fn(
3, 4, 9, -3
)
expect(result).toEqual([ -3, 9, -3 ])
})
```
TypeScript test
```typescript
import {juxt} from 'rambda'
describe('R.juxt', () => {
it('happy', () => {
const fn = juxt([Math.min, Math.max])
const result = fn(3, 4, 9, -3)
result // $ExpectType [number, number]
})
})
```
[](#juxt)
### keys
```typescript
keys(x: T): (keyof T & string)[]
```
It applies `Object.keys` over `x` and returns its keys.
Try this R.keys example in Rambda REPL
All TypeScript definitions
```typescript
keys(x: T): (keyof T & string)[];
keys(x: T): string[];
```
R.keys source
```javascript
export function keys(x){
return Object.keys(x)
}
```
Tests
```javascript
import { keys } from './keys.js'
test('happy', () => {
expect(keys({ a : 1 })).toEqual([ 'a' ])
})
```
[](#keys)
### last
```typescript
last(str: ''): undefined
```
It returns the last element of `input`, as the `input` can be either a string or an array.
Try this R.last example in Rambda REPL
All TypeScript definitions
```typescript
last(str: ''): undefined;
last(str: string): string;
last(list: never[]): undefined;
last(array: T): LastArrayElement
last(array: T): LastArrayElement
```
R.last source
```javascript
export function last(listOrString){
if (typeof listOrString === 'string'){
return listOrString[ listOrString.length - 1 ] || ''
}
return listOrString[ listOrString.length - 1 ]
}
```
Tests
```javascript
import { last } from './last.js'
test('with list', () => {
expect(last([ 1, 2, 3 ])).toBe(3)
expect(last([])).toBeUndefined()
})
test('with string', () => {
expect(last('abc')).toBe('c')
expect(last('')).toBe('')
})
```
[](#last)
### lastIndexOf
```typescript
lastIndexOf(target: T, list: T[]): number
```
It returns the last index of `target` in `list` array.
`R.equals` is used to determine equality between `target` and members of `list`.
If there is no such index, then `-1` is returned.
Try this R.lastIndexOf example in Rambda REPL
All TypeScript definitions
```typescript
lastIndexOf(target: T, list: T[]): number;
lastIndexOf(target: T): (list: T[]) => number;
```
R.lastIndexOf source
```javascript
import { _lastIndexOf } from './equals.js'
export function lastIndexOf(valueToFind, list){
if (arguments.length === 1){
return _list => _lastIndexOf(valueToFind, _list)
}
return _lastIndexOf(valueToFind, list)
}
```
Tests
```javascript
import { lastIndexOf as lastIndexOfRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './indexOf.spec.js'
import { lastIndexOf } from './lastIndexOf.js'
test('with NaN', () => {
expect(lastIndexOf(NaN, [ NaN ])).toBe(0)
})
test('will throw with bad input', () => {
expect(lastIndexOfRamda([], true)).toBe(-1)
expect(() => indexOf([], true)).toThrowErrorMatchingInlineSnapshot('"indexOf is not defined"')
})
test('without list of objects - no R.equals', () => {
expect(lastIndexOf(3, [ 1, 2, 3, 4 ])).toBe(2)
expect(lastIndexOf(10)([ 1, 2, 3, 4 ])).toBe(-1)
})
test('list of objects uses R.equals', () => {
const listOfObjects = [ { a : 1 }, { b : 2 }, { c : 3 } ]
expect(lastIndexOf({ c : 4 }, listOfObjects)).toBe(-1)
expect(lastIndexOf({ c : 3 }, listOfObjects)).toBe(2)
})
test('list of arrays uses R.equals', () => {
const listOfLists = [ [ 1 ], [ 2, 3 ], [ 2, 3, 4 ], [ 2, 3 ], [ 1 ], [] ]
expect(lastIndexOf([], listOfLists)).toBe(5)
expect(lastIndexOf([ 1 ], listOfLists)).toBe(4)
expect(lastIndexOf([ 2, 3, 4 ], listOfLists)).toBe(2)
expect(lastIndexOf([ 2, 3, 5 ], listOfLists)).toBe(-1)
})
test('with string as iterable', () => {
expect(() => lastIndexOf('a', 'abc')).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of abc"')
expect(lastIndexOfRamda('a', 'abc')).toBe(0)
})
describe('brute force', () => {
compareCombinations({
fn : lastIndexOf,
fnRamda : lastIndexOfRamda,
firstInput : possibleTargets,
secondInput : possibleIterables,
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 34,
"RESULTS_MISMATCH": 0,
"SHOULD_NOT_THROW": 51,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 170,
}
`)
},
})
})
```
TypeScript test
```typescript
import {lastIndexOf} from 'rambda'
const list = [1, 2, 3]
describe('R.lastIndexOf', () => {
it('happy', () => {
const result = lastIndexOf(2, list)
result // $ExpectType number
})
it('curried', () => {
const result = lastIndexOf(2)(list)
result // $ExpectType number
})
})
```
[](#lastIndexOf)
### length
```typescript
length(input: T[]): number
```
It returns the `length` property of list or string `input`.
Try this R.length example in Rambda REPL
All TypeScript definitions
```typescript
length(input: T[]): number;
```
R.length source
```javascript
import { isArray } from './_internals/isArray.js'
export function length(x){
if (isArray(x)) return x.length
if (typeof x === 'string') return x.length
return NaN
}
```
Tests
```javascript
import { length as lengthRamda } from 'ramda'
import { length } from './length.js'
test('happy', () => {
expect(length('foo')).toBe(3)
expect(length([ 1, 2, 3 ])).toBe(3)
expect(length([])).toBe(0)
})
test('with empty string', () => {
expect(length('')).toBe(0)
})
test('with bad input returns NaN', () => {
expect(length(0)).toBeNaN()
expect(length({})).toBeNaN()
expect(length(null)).toBeNaN()
expect(length(undefined)).toBeNaN()
})
test('with length as property', () => {
const input1 = { length : '123' }
const input2 = { length : null }
const input3 = { length : '' }
expect(length(input1)).toBeNaN()
expect(lengthRamda(input1)).toBeNaN()
expect(length(input2)).toBeNaN()
expect(lengthRamda(input2)).toBeNaN()
expect(length(input3)).toBeNaN()
expect(lengthRamda(input3)).toBeNaN()
})
```
[](#length)
### lens
```typescript
lens(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens
```
It returns a `lens` for the given `getter` and `setter` functions.
The `getter` **gets** the value of the focus; the `setter` **sets** the value of the focus.
The setter should not mutate the data structure.
Try this R.lens example in Rambda REPL
All TypeScript definitions
```typescript
lens(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens;
```
R.lens source
```javascript
export function lens(getter, setter){
return function (functor){
return function (target){
return functor(getter(target)).map(focus => setter(focus, target))
}
}
}
```
TypeScript test
```typescript
import {lens, assoc, lensProp, view, lensIndex, lensPath} from 'rambda'
interface Input {
foo: string,
}
const testObject: Input = {
foo: 'Jazz',
}
describe('R.lens', () => {
it('happy', () => {
const fn = lens((x: Input) => {
x.foo // $ExpectType string
return x.foo
}, assoc('name'))
fn // $ExpectType Lens
})
})
describe('R.lensProp', () => {
it('happy', () => {
const result = view(lensProp('foo'), testObject)
result // $ExpectType string
})
})
describe('R.lensIndex', () => {
const testList: Input[] = [{foo: 'bar'}, {foo: 'baz'}]
it('happy', () => {
const result = view(lensIndex(0), testList)
result // $ExpectType Input
result.foo // $ExpectType string
})
})
describe('R.lensPath', () => {
const path = lensPath(['bar', 'a'])
it('happy', () => {
const result = view(path, testObject)
result // $ExpectType string
})
})
describe('R.view', () => {
const fooLens = lens((x: Input) => {
return x.foo
}, assoc('foo'))
it('happt', () => {
const result = view(fooLens, testObject)
result // $ExpectType string
})
})
```
[](#lens)
### lensIndex
```typescript
lensIndex(n: number): Lens
```
It returns a lens that focuses on specified `index`.
Try this R.lensIndex example in Rambda REPL
All TypeScript definitions
```typescript
lensIndex(n: number): Lens;
lensIndex(n: N): Lens;
```
R.lensIndex source
```javascript
import { lens } from './lens.js'
import { nth } from './nth.js'
import { update } from './update.js'
export function lensIndex(index){
return lens(nth(index), update(index))
}
```
Tests
```javascript
import { compose } from './compose.js'
import { keys } from './keys.js'
import { lensIndex } from './lensIndex.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'
const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]
test('focuses list element at the specified index', () => {
expect(view(lensIndex(0), testList)).toEqual({ a : 1 })
})
test('returns undefined if the specified index does not exist', () => {
expect(view(lensIndex(10), testList)).toBeUndefined()
})
test('sets the list value at the specified index', () => {
expect(set(
lensIndex(0), 0, testList
)).toEqual([ 0, { b : 2 }, { c : 3 } ])
})
test('applies function to the value at the specified list index', () => {
expect(over(
lensIndex(2), keys, testList
)).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])
})
test('can be composed', () => {
const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ]
const composedLens = compose(lensIndex(1), lensIndex(0))
expect(view(composedLens, nestedList)).toBe(10)
})
test('set s (get s) === s', () => {
expect(set(
lensIndex(0), view(lensIndex(0), testList), testList
)).toEqual(testList)
})
test('get (set s v) === v', () => {
expect(view(lensIndex(0), set(
lensIndex(0), 0, testList
))).toBe(0)
})
test('get (set(set s v1) v2) === v2', () => {
expect(view(lensIndex(0),
set(
lensIndex(0), 11, set(
lensIndex(0), 10, testList
)
))).toBe(11)
})
```
[](#lensIndex)
### lensPath
It returns a lens that focuses on specified `path`.
Try this R.lensPath example in Rambda REPL
[](#lensPath)
### lensProp
```typescript
lensProp(prop: K): Lens
```
It returns a lens that focuses on specified property `prop`.
Try this R.lensProp example in Rambda REPL
All TypeScript definitions
```typescript
lensProp(prop: K): Lens;
```
R.lensProp source
```javascript
import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'
export function lensProp(key){
return lens(prop(key), assoc(key))
}
```
Tests
```javascript
import { compose } from './compose.js'
import { identity } from './identity.js'
import { inc } from './inc.js'
import { lensProp } from './lensProp.js'
import { over } from './over.js'
import { set } from './set.js'
import { view } from './view.js'
const testObj = {
a : 1,
b : 2,
c : 3,
}
test('focuses object the specified object property', () => {
expect(view(lensProp('a'), testObj)).toBe(1)
})
test('returns undefined if the specified property does not exist', () => {
expect(view(lensProp('X'), testObj)).toBeUndefined()
})
test('sets the value of the object property specified', () => {
expect(set(
lensProp('a'), 0, testObj
)).toEqual({
a : 0,
b : 2,
c : 3,
})
})
test('adds the property to the object if it doesn\'t exist', () => {
expect(set(
lensProp('d'), 4, testObj
)).toEqual({
a : 1,
b : 2,
c : 3,
d : 4,
})
})
test('applies function to the value of the specified object property', () => {
expect(over(
lensProp('a'), inc, testObj
)).toEqual({
a : 2,
b : 2,
c : 3,
})
})
test('applies function to undefined and adds the property if it doesn\'t exist', () => {
expect(over(
lensProp('X'), identity, testObj
)).toEqual({
a : 1,
b : 2,
c : 3,
X : undefined,
})
})
test('can be composed', () => {
const nestedObj = {
a : { b : 1 },
c : 2,
}
const composedLens = compose(lensProp('a'), lensProp('b'))
expect(view(composedLens, nestedObj)).toBe(1)
})
test('set s (get s) === s', () => {
expect(set(
lensProp('a'), view(lensProp('a'), testObj), testObj
)).toEqual(testObj)
})
test('get (set s v) === v', () => {
expect(view(lensProp('a'), set(
lensProp('a'), 0, testObj
))).toBe(0)
})
test('get (set(set s v1) v2) === v2', () => {
expect(view(lensProp('a'),
set(
lensProp('a'), 11, set(
lensProp('a'), 10, testObj
)
))).toBe(11)
})
```
[](#lensProp)
### map
```typescript
map(fn: ObjectIterator, iterable: Dictionary): Dictionary
```
It returns the result of looping through `iterable` with `fn`.
It works with both array and object.
Try this R.map example in Rambda REPL
All TypeScript definitions
```typescript
map(fn: ObjectIterator, iterable: Dictionary): Dictionary;
map(fn: Iterator, iterable: T[]): U[];
map(fn: Iterator): (iterable: T[]) => U[];
map(fn: ObjectIterator): (iterable: Dictionary) => Dictionary;
map(fn: Iterator): (iterable: T[]) => T[];
map(fn: Iterator, iterable: T[]): T[];
```
R.map source
```javascript
import { INCORRECT_ITERABLE_INPUT } from './_internals/constants.js'
import { isArray } from './_internals/isArray.js'
import { keys } from './_internals/keys.js'
export function mapArray(
fn, list, isIndexed = false
){
let index = 0
const willReturn = Array(list.length)
while (index < list.length){
willReturn[ index ] = isIndexed ? fn(list[ index ], index) : fn(list[ index ])
index++
}
return willReturn
}
export function mapObject(fn, obj){
if (arguments.length === 1){
return _obj => mapObject(fn, _obj)
}
let index = 0
const objKeys = keys(obj)
const len = objKeys.length
const willReturn = {}
while (index < len){
const key = objKeys[ index ]
willReturn[ key ] = fn(
obj[ key ], key, obj
)
index++
}
return willReturn
}
export const mapObjIndexed = mapObject
export function map(fn, iterable){
if (arguments.length === 1) return _iterable => map(fn, _iterable)
if (!iterable){
throw new Error(INCORRECT_ITERABLE_INPUT)
}
if (isArray(iterable)) return mapArray(fn, iterable)
return mapObject(fn, iterable)
}
```
Tests
```javascript
import { map as mapRamda } from 'ramda'
import { map } from './map.js'
const double = x => x * 2
describe('with array', () => {
it('happy', () => {
expect(map(double, [ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
})
it('curried', () => {
expect(map(double)([ 1, 2, 3 ])).toEqual([ 2, 4, 6 ])
})
})
describe('with object', () => {
const obj = {
a : 1,
b : 2,
}
it('happy', () => {
expect(map(double, obj)).toEqual({
a : 2,
b : 4,
})
})
it('property as second and input object as third argument', () => {
const obj = {
a : 1,
b : 2,
}
const iterator = (
val, prop, inputObject
) => {
expect(prop).toBeString()
expect(inputObject).toEqual(obj)
return val * 2
}
expect(map(iterator)(obj)).toEqual({
a : 2,
b : 4,
})
})
})
test('bad inputs difference between Ramda and Rambda', () => {
expect(() => map(double, null)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"')
expect(() => map(double)(undefined)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"')
expect(() => mapRamda(double, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'fantasy-land/map\')"')
expect(() =>
mapRamda(double, undefined)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of undefined (reading \'fantasy-land/map\')"')
})
```
TypeScript test
```typescript
import {map} from 'rambda'
describe('R.map with arrays', () => {
it('iterable returns the same type as the input', () => {
const result = map(
(x: number) => {
x // $ExpectType number
return x + 2
},
[1, 2, 3]
)
result // $ExpectType number[]
})
it('iterable returns the same type as the input - curried', () => {
const result = map((x: number) => {
x // $ExpectType number
return x + 2
})([1, 2, 3])
result // $ExpectType number[]
})
it('iterable returns different type as the input', () => {
const result = map(
(x: number) => {
x // $ExpectType number
return String(x)
},
[1, 2, 3]
)
result // $ExpectType string[]
})
})
describe('R.map with objects', () => {
it('iterable with all three arguments - curried', () => {
// It requires dummy third typing argument
// in order to identify compared to curry typings for arrays
// ============================================
const result = map((a, b, c) => {
a // $ExpectType number
b // $ExpectType string
c // $ExpectType Dictionary
return `${a}`
})({a: 1, b: 2})
result // $ExpectType Dictionary
})
it('iterable with all three arguments', () => {
const result = map(
(a, b, c) => {
a // $ExpectType number
b // $ExpectType string
c // $ExpectType Dictionary
return `${a}`
},
{a: 1, b: 2}
)
result // $ExpectType Dictionary
})
it('iterable with property argument', () => {
const result = map(
(a, b) => {
a // $ExpectType number
b // $ExpectType string
return `${a}`
},
{a: 1, b: 2}
)
result // $ExpectType Dictionary
})
it('iterable with no property argument', () => {
const result = map(
a => {
a // $ExpectType number
return `${a}`
},
{a: 1, b: 2}
)
result // $ExpectType Dictionary
})
})
```
[](#map)
### mapObjIndexed
```typescript
mapObjIndexed(fn: ObjectIterator, iterable: Dictionary): Dictionary
```
It works the same way as `R.map` does for objects. It is added as Ramda also has this method.
Try this R.mapObjIndexed example in Rambda REPL
All TypeScript definitions
```typescript
mapObjIndexed(fn: ObjectIterator, iterable: Dictionary): Dictionary;
mapObjIndexed(fn: ObjectIterator, iterable: Dictionary): Dictionary;
mapObjIndexed(fn: ObjectIterator): (iterable: Dictionary) => Dictionary;
mapObjIndexed(fn: ObjectIterator): (iterable: Dictionary) => Dictionary;
```
TypeScript test
```typescript
import {mapObjIndexed} from 'rambda'
const obj = {a: 1, b: 2, c: 3}
describe('R.mapObjIndexed', () => {
it('without type transform', () => {
const result = mapObjIndexed((x, prop, obj) => {
x // $ExpectType number
prop // $ExpectType string
obj // $ExpectType Dictionary
return x + 2
}, obj)
result // $ExpectType Dictionary
})
it('without type transform - curried', () => {
const result = mapObjIndexed((x, prop, obj) => {
x // $ExpectType number
prop // $ExpectType string
obj // $ExpectType Dictionary
return x + 2
})(obj)
result // $ExpectType Dictionary
})
it('change of type', () => {
const result = mapObjIndexed((x, prop, obj) => {
x // $ExpectType number
prop // $ExpectType string
obj // $ExpectType Dictionary
return String(x + 2)
}, obj)
result // $ExpectType Dictionary
})
it('change of type - curried', () => {
const result = mapObjIndexed((x, prop, obj) => {
x // $ExpectType number
prop // $ExpectType string
obj // $ExpectType Dictionary
return String(x + 2)
})(obj)
result // $ExpectType Dictionary
})
})
```
[](#mapObjIndexed)
### match
```typescript
match(regExpression: RegExp, str: string): string[]
```
Curried version of `String.prototype.match` which returns empty array, when there is no match.
Try this R.match example in Rambda REPL
All TypeScript definitions
```typescript
match(regExpression: RegExp, str: string): string[];
match(regExpression: RegExp): (str: string) => string[];
```
R.match source
```javascript
export function match(pattern, input){
if (arguments.length === 1) return _input => match(pattern, _input)
const willReturn = input.match(pattern)
return willReturn === null ? [] : willReturn
}
```
Tests
```javascript
import { equals } from './equals.js'
import { match } from './match.js'
test('happy', () => {
expect(match(/a./g)('foo bar baz')).toEqual([ 'ar', 'az' ])
})
test('fallback', () => {
expect(match(/a./g)('foo')).toEqual([])
})
test('with string', () => {
expect(match('a', 'foo')).toEqual([])
expect(equals(match('o', 'foo'), [ 'o' ])).toBeTrue()
})
test('throwing', () => {
expect(() => {
match(/a./g, null)
}).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'match\')"')
})
```
TypeScript test
```typescript
import {match} from 'rambda'
const str = 'foo bar'
describe('R.match', () => {
it('happy', () => {
const result = match(/foo/, str)
result // $ExpectType string[]
})
it('curried', () => {
const result = match(/foo/)(str)
result // $ExpectType string[]
})
})
```
[](#match)
### mathMod
`R.mathMod` behaves like the modulo operator should mathematically, unlike the `%` operator (and by extension, `R.modulo`). So while `-17 % 5` is `-2`, `mathMod(-17, 5)` is `3`.
Try this R.mathMod example in Rambda REPL
[](#mathMod)
### max
It returns the greater value between `x` and `y`.
Try this R.max example in Rambda REPL
[](#max)
### maxBy
It returns the greater value between `x` and `y` according to `compareFn` function.
Try this R.maxBy example in Rambda REPL
[](#maxBy)
### mean
```typescript
mean(list: number[]): number
```
It returns the mean value of `list` input.
Try this R.mean example in Rambda REPL
All TypeScript definitions
```typescript
mean(list: number[]): number;
```
R.mean source
```javascript
import { sum } from './sum.js'
export function mean(list){
return sum(list) / list.length
}
```
Tests
```javascript
import { mean } from './mean.js'
test('happy', () => {
expect(mean([ 2, 7 ])).toBe(4.5)
})
test('with NaN', () => {
expect(mean([])).toBeNaN()
})
```
TypeScript test
```typescript
import {mean} from 'rambda'
describe('R.mean', () => {
it('happy', () => {
const result = mean([1, 2, 3])
result // $ExpectType number
})
})
```
[](#mean)
### median
```typescript
median(list: number[]): number
```
It returns the median value of `list` input.
Try this R.median example in Rambda REPL
All TypeScript definitions
```typescript
median(list: number[]): number;
```
R.median source
```javascript
import { mean } from './mean.js'
export function median(list){
const len = list.length
if (len === 0) return NaN
const width = 2 - len % 2
const idx = (len - width) / 2
return mean(Array.prototype.slice
.call(list, 0)
.sort((a, b) => {
if (a === b) return 0
return a < b ? -1 : 1
})
.slice(idx, idx + width))
}
```
Tests
```javascript
import { median } from './median.js'
test('happy', () => {
expect(median([ 2 ])).toBe(2)
expect(median([ 7, 2, 10, 2, 9 ])).toBe(7)
})
test('with empty array', () => {
expect(median([])).toBeNaN()
})
```
TypeScript test
```typescript
import {median} from 'rambda'
describe('R.median', () => {
it('happy', () => {
const result = median([1, 2, 3])
result // $ExpectType number
})
})
```
[](#median)
### merge
Same as `R.mergeRight`.
[](#merge)
### mergeAll
```typescript
mergeAll(list: object[]): T
```
It merges all objects of `list` array sequentially and returns the result.
Try this R.mergeAll example in Rambda REPL
All TypeScript definitions
```typescript
mergeAll(list: object[]): T;
mergeAll(list: object[]): object;
```
R.mergeAll source
```javascript
import { map } from './map.js'
import { mergeRight } from './mergeRight.js'
export function mergeAll(arr){
let willReturn = {}
map(val => {
willReturn = mergeRight(willReturn, val)
}, arr)
return willReturn
}
```
Tests
```javascript
import { mergeAll } from './mergeAll.js'
test('case 1', () => {
const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ]
const expectedResult = {
a : 1,
b : 2,
c : 3,
}
expect(mergeAll(arr)).toEqual(expectedResult)
})
test('case 2', () => {
expect(mergeAll([ { foo : 1 }, { bar : 2 }, { baz : 3 } ])).toEqual({
foo : 1,
bar : 2,
baz : 3,
})
})
describe('acts as if nil values are simply empty objects', () => {
it('if the first object is nil', () => {
expect(mergeAll([ null, { foo : 1 }, { foo : 2 }, { bar : 2 } ])).toEqual({
foo : 2,
bar : 2,
})
})
it('if the last object is nil', () => {
expect(mergeAll([ { foo : 1 }, { foo : 2 }, { bar : 2 }, undefined ])).toEqual({
foo : 2,
bar : 2,
})
})
it('if an intermediate object is nil', () => {
expect(mergeAll([ { foo : 1 }, { foo : 2 }, null, { bar : 2 } ])).toEqual({
foo : 2,
bar : 2,
})
})
})
```
TypeScript test
```typescript
import {mergeAll} from 'rambda'
describe('R.mergeAll', () => {
it('with passing type', () => {
interface Output {
foo: number,
bar: number,
}
const result = mergeAll([{foo: 1}, {bar: 2}])
result.foo // $ExpectType number
result.bar // $ExpectType number
})
it('without passing type', () => {
const result = mergeAll([{foo: 1}, {bar: 2}])
result // $ExpectType unknown
})
})
```
[](#mergeAll)
### mergeDeepRight
```typescript
mergeDeepRight(target: object, newProps: object): Output
```
Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:
- and both values are objects, the two values will be recursively merged
- otherwise the value from the second object will be used.
All TypeScript definitions
```typescript
mergeDeepRight(target: object, newProps: object): Output;
mergeDeepRight(target: object): (newProps: object) => Output;
```
R.mergeDeepRight source
```javascript
import { clone } from './clone.js'
import { type } from './type.js'
export function mergeDeepRight(target, source){
if (arguments.length === 1){
return sourceHolder => mergeDeepRight(target, sourceHolder)
}
const willReturn = clone(target)
Object.keys(source).forEach(key => {
if (type(source[ key ]) === 'Object'){
if (type(target[ key ]) === 'Object'){
willReturn[ key ] = mergeDeepRight(target[ key ], source[ key ])
} else {
willReturn[ key ] = source[ key ]
}
} else {
willReturn[ key ] = source[ key ]
}
})
return willReturn
}
```
Tests
```javascript
import { mergeDeepRight } from './mergeDeepRight.js'
const student = {
name : 'foo',
age : 10,
contact : {
a : 1,
email : '[email protected]',
},
}
const teacher = {
age : 40,
contact : { email : '[email protected]' },
songs : { title : 'Remains the same' },
}
test('when merging object with lists inside them', () => {
const a = {
a : [ 1, 2, 3 ],
b : [ 4, 5, 6 ],
}
const b = {
a : [ 7, 8, 9 ],
b : [ 10, 11, 12 ],
}
const result = mergeDeepRight(a, b)
const expected = {
a : [ 7, 8, 9 ],
b : [ 10, 11, 12 ],
}
expect(result).toEqual(expected)
})
test('happy', () => {
const result = mergeDeepRight(student, teacher)
const curryResult = mergeDeepRight(student)(teacher)
const expected = {
age : 40,
name : 'foo',
contact : {
a : 1,
email : '[email protected]',
},
songs : { title : 'Remains the same' },
}
expect(result).toEqual(expected)
expect(curryResult).toEqual(expected)
})
test('issue 650', () => {
expect(Object.keys(mergeDeepRight({ a : () => {} }, { b : () => {} }))).toEqual([
'a',
'b',
])
})
test('ramda compatible test 1', () => {
const a = {
w : 1,
x : 2,
y : { z : 3 },
}
const b = {
a : 4,
b : 5,
c : { d : 6 },
}
const result = mergeDeepRight(a, b)
const expected = {
w : 1,
x : 2,
y : { z : 3 },
a : 4,
b : 5,
c : { d : 6 },
}
expect(result).toEqual(expected)
})
test('ramda compatible test 2', () => {
const a = {
a : {
b : 1,
c : 2,
},
y : 0,
}
const b = {
a : {
b : 3,
d : 4,
},
z : 0,
}
const result = mergeDeepRight(a, b)
const expected = {
a : {
b : 3,
c : 2,
d : 4,
},
y : 0,
z : 0,
}
expect(result).toEqual(expected)
})
test('ramda compatible test 3', () => {
const a = {
w : 1,
x : { y : 2 },
}
const result = mergeDeepRight(a, { x : { y : 3 } })
const expected = {
w : 1,
x : { y : 3 },
}
expect(result).toEqual(expected)
})
test('functions are not discarded', () => {
const obj = { foo : () => {} }
expect(typeof mergeDeepRight(obj, {}).foo).toBe('function')
})
```
TypeScript test
```typescript
import {mergeDeepRight} from 'rambda'
interface Output {
foo: {
bar: number,
},
}
describe('R.mergeDeepRight', () => {
const result = mergeDeepRight({foo: {bar: 1}}, {foo: {bar: 2}})
result.foo.bar // $ExpectType number
})
```
[](#mergeDeepRight)
### mergeLeft
```typescript
mergeLeft(newProps: object, target: object): Output
```
Same as `R.merge`, but in opposite direction.
Try this R.mergeLeft example in Rambda REPL
All TypeScript definitions
```typescript
mergeLeft(newProps: object, target: object): Output;
mergeLeft(newProps: object): (target: object) => Output;
```
R.mergeLeft source
```javascript
import { mergeRight } from './mergeRight.js'
export function mergeLeft(x, y){
if (arguments.length === 1) return _y => mergeLeft(x, _y)
return mergeRight(y, x)
}
```
Tests
```javascript
import { mergeLeft } from './mergeLeft.js'
const obj = {
foo : 1,
bar : 2,
}
test('happy', () => {
expect(mergeLeft({ bar : 20 }, obj)).toEqual({
foo : 1,
bar : 20,
})
})
test('curry', () => {
expect(mergeLeft({ baz : 3 })(obj)).toEqual({
foo : 1,
bar : 2,
baz : 3,
})
})
test('when undefined or null instead of object', () => {
expect(mergeLeft(null, undefined)).toEqual({})
expect(mergeLeft(obj, null)).toEqual(obj)
expect(mergeLeft(obj, undefined)).toEqual(obj)
expect(mergeLeft(undefined, obj)).toEqual(obj)
})
```
TypeScript test
```typescript
import {mergeLeft} from 'rambda'
interface Output {
foo: number,
bar: number,
}
describe('R.mergeLeft', () => {
const result = mergeLeft({foo: 1}, {bar: 2})
const curriedResult = mergeLeft({foo: 1})({bar: 2})
result.foo // $ExpectType number
result.bar // $ExpectType number
curriedResult.bar // $ExpectType number
})
```
[](#mergeLeft)
### mergeRight
It creates a copy of `target` object with overwritten `newProps` properties. Previously known as `R.merge` but renamed after Ramda did the same.
Try this R.mergeRight example in Rambda REPL
[](#mergeRight)
### mergeWith
```typescript
mergeWith(fn: (x: any, z: any) => any, a: Record, b: Record): Record
```
It takes two objects and a function, which will be used when there is an overlap between the keys.
Try this R.mergeWith example in Rambda REPL
All TypeScript definitions
```typescript
mergeWith(fn: (x: any, z: any) => any, a: Record, b: Record): Record;
mergeWith(fn: (x: any, z: any) => any, a: Record, b: Record): Output;
mergeWith(fn: (x: any, z: any) => any, a: Record): (b: Record) => Record;
mergeWith(fn: (x: any, z: any) => any, a: Record): (b: Record) => Output;
mergeWith(fn: (x: any, z: any) => any): (a: U, b: V) => Record;
mergeWith(fn: (x: any, z: any) => any): (a: U, b: V) => Output;
```
R.mergeWith source
```javascript
import { curry } from './curry.js'
export function mergeWithFn(
mergeFn, aInput, bInput
){
const a = aInput ?? {}
const b = bInput ?? {}
const willReturn = {}
Object.keys(a).forEach(key => {
if (b[ key ] === undefined) willReturn[ key ] = a[ key ]
else willReturn[ key ] = mergeFn(a[ key ], b[ key ])
})
Object.keys(b).forEach(key => {
if (willReturn[ key ] !== undefined) return
if (a[ key ] === undefined) willReturn[ key ] = b[ key ]
else willReturn[ key ] = mergeFn(a[ key ], b[ key ])
})
return willReturn
}
export const mergeWith = curry(mergeWithFn)
```
Tests
```javascript
import { concat } from './concat.js'
import { mergeWithFn } from './mergeWith.js'
test('happy', () => {
const result = mergeWithFn(
concat,
{
a : true,
values : [ 10, 20 ],
},
{
b : true,
values : [ 15, 35 ],
}
)
const expected = {
a : true,
b : true,
values : [ 10, 20, 15, 35 ],
}
expect(result).toEqual(expected)
})
// https://github.com/ramda/ramda/pull/3222/files#diff-d925d9188b478d2f1d4b26012c6dddac374f9e9d7a336604d654b9a113bfc857
describe('acts as if nil values are simply empty objects', () => {
it('if the first object is nil and the second empty', () => {
expect(mergeWithFn(
concat, undefined, {}
)).toEqual({})
})
it('if the first object is empty and the second nil', () => {
expect(mergeWithFn(
concat, {}, null
)).toEqual({})
})
it('if both objects are nil', () => {
expect(mergeWithFn(
concat, undefined, null
)).toEqual({})
})
it('if the first object is not empty and the second is nil', () => {
expect(mergeWithFn(
concat, { a : 'a' }, null
)).toEqual({ a : 'a' })
})
it('if the first object is nil and the second is not empty', () => {
expect(mergeWithFn(
concat, undefined, { a : 'a' }
)).toEqual({ a : 'a' })
})
})
```
TypeScript test
```typescript
import {concat, mergeWith} from 'rambda'
interface Output {
a: boolean,
b: boolean,
values: number[],
}
const A = {
a: true,
values: [10, 20],
}
const B = {
b: true,
values: [15, 35],
}
describe('R.mergeWith', () => {
test('no curry | without explicit types', () => {
const result = mergeWith(concat, A, B)
result // $ExpectType Record
})
test('no curry | with explicit types', () => {
const result = mergeWith(concat, A, B)
result // $ExpectType Output
})
test('curry 1 | without explicit types', () => {
const result = mergeWith(concat, A)(B)
result // $ExpectType Record
})
test('curry 1 | with explicit types', () => {
const result = mergeWith(concat, A)(B)
result // $ExpectType Output
})
test('curry 2 | without explicit types', () => {
const result = mergeWith(concat)(A, B)
result // $ExpectType Record
})
test('curry 2 | with explicit types', () => {
const result = mergeWith(concat)(A, B)
result // $ExpectType Output
})
})
```
[](#mergeWith)
### min
It returns the lesser value between `x` and `y`.
Try this R.min example in Rambda REPL
[](#min)
### minBy
It returns the lesser value between `x` and `y` according to `compareFn` function.
Try this R.minBy example in Rambda REPL
[](#minBy)
### modify
```typescript
modify(
prop: K,
fn: (a: T[K]) => P,
obj: T,
): Omit & Record
```
Try this R.modify example in Rambda REPL
All TypeScript definitions
```typescript
modify(
prop: K,
fn: (a: T[K]) => P,
obj: T,
): Omit & Record;
modify(
prop: K,
fn: (a: A) => P,
): >(target: T) => Omit & Record;
```
R.modify source
```javascript
import { isArray } from './_internals/isArray.js'
import { isIterable } from './_internals/isIterable.js'
import { curry } from './curry.js'
import { updateFn } from './update.js'
function modifyFn(
property, fn, iterable
){
if (!isIterable(iterable)) return iterable
if (iterable[ property ] === undefined) return iterable
if (isArray(iterable)){
return updateFn(
property, fn(iterable[ property ]), iterable
)
}
return {
...iterable,
[ property ] : fn(iterable[ property ]),
}
}
export const modify = curry(modifyFn)
```
Tests
```javascript
import { modify as modifyRamda } from 'ramda'
import { compareCombinations, FALSY_VALUES } from './_internals/testUtils.js'
import { add } from './add.js'
import { compose } from './compose.js'
import { modify } from './modify.js'
const person = {
name : 'foo',
age : 20,
}
test('happy', () => {
expect(modify(
'age', x => x + 1, person
)).toEqual({
name : 'foo',
age : 21,
})
})
test('property is missing', () => {
expect(modify(
'foo', x => x + 1, person
)).toEqual(person)
})
test('adjust if `array` at the given key with the `transformation` function', () => {
expect(modify(
1, add(1), [ 100, 1400 ]
)).toEqual([ 100, 1401 ])
})
describe('ignores transformations if the input value is not Array and Object', () => {
;[ 42, undefined, null, '' ].forEach(value => {
it(`${ value }`, () => {
expect(modify(
'a', add(1), value
)).toEqual(value)
})
})
})
const possibleProperties = [ ...FALSY_VALUES, 'foo', 0 ]
const possibleTransformers = [
...FALSY_VALUES,
add(1),
add('foo'),
compose,
String,
]
const possibleObjects = [
...FALSY_VALUES,
{},
[ 1, 2, 3 ],
{
a : 1,
foo : 2,
},
{
a : 1,
foo : [ 1 ],
},
{
a : 1,
foo : 'bar',
},
]
describe('brute force', () => {
compareCombinations({
fn : modify,
fnRamda : modifyRamda,
firstInput : possibleProperties,
secondInput : possibleTransformers,
thirdInput : possibleObjects,
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 0,
"RESULTS_MISMATCH": 0,
"SHOULD_NOT_THROW": 0,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 630,
}
`)
},
})
})
```
TypeScript test
```typescript
import {modify, add} from 'rambda'
const person = {name: 'James', age: 20}
describe('R.modify', () => {
it('happy', () => {
const {age} = modify('age', add(1), person)
const {age: ageAsString} = modify('age', String, person)
age // $ExpectType number
ageAsString // $ExpectType string
})
it('curried', () => {
const {age} = modify('age', add(1))(person)
age // $ExpectType number
})
})
```
[](#modify)
### modifyPath
```typescript
modifyPath>(path: Path, fn: (x: any) => unknown, object: Record): T
```
It changes a property of object on the base of provided path and transformer function.
Try this R.modifyPath example in Rambda REPL
All TypeScript definitions
```typescript
modifyPath>(path: Path, fn: (x: any) => unknown, object: Record): T;
modifyPath>(path: Path, fn: (x: any) => unknown): (object: Record) => T;
modifyPath>(path: Path): (fn: (x: any) => unknown) => (object: Record) => T;
```
R.modifyPath source
```javascript
import { createPath } from './_internals/createPath.js'
import { isArray } from './_internals/isArray.js'
import { assoc } from './assoc.js'
import { curry } from './curry.js'
import { path as pathModule } from './path.js'
export function modifyPathFn(
pathInput, fn, object
){
const path = createPath(pathInput)
if (path.length === 1){
return {
...object,
[ path[ 0 ] ] : fn(object[ path[ 0 ] ]),
}
}
if (pathModule(path, object) === undefined) return object
const val = modifyPath(
Array.prototype.slice.call(path, 1),
fn,
object[ path[ 0 ] ]
)
if (val === object[ path[ 0 ] ]){
return object
}
return assoc(
path[ 0 ], val, object
)
}
export const modifyPath = curry(modifyPathFn)
```
Tests
```javascript
import { modifyPath } from './modifyPath.js'
test('happy', () => {
const result = modifyPath(
'a.b.c', x => x + 1, { a : { b : { c : 1 } } }
)
expect(result).toEqual({ a : { b : { c : 2 } } })
})
test('with array', () => {
const input = { foo : [ { bar : '123' } ] }
const result = modifyPath(
'foo.0.bar', x => x + 'foo', input
)
expect(result).toEqual({ foo : { 0 : { bar : '123foo' } } })
})
```
TypeScript test
```typescript
import {modifyPath} from 'rambda'
const obj = {a: {b: {c: 1}}}
describe('R.modifyPath', () => {
it('happy', () => {
const result = modifyPath('a.b.c', (x: number) => x + 1, obj)
result // $ExpectType Record
})
it('explicit return type', () => {
interface Foo extends Record {
a: 1,
}
const result = modifyPath('a.b.c', (x: number) => x + 1, obj)
result // $ExpectType Foo
})
})
```
[](#modifyPath)
### modulo
Curried version of `x%y`.
Try this R.modulo example in Rambda REPL
[](#modulo)
### move
It returns a copy of `list` with exchanged `fromIndex` and `toIndex` elements.
Try this R.move example in Rambda REPL
[](#move)
### multiply
Curried version of `x*y`.
Try this R.multiply example in Rambda REPL
[](#multiply)
### negate
Try this R.negate example in Rambda REPL
[](#negate)
### none
```typescript
none(predicate: (x: T) => boolean, list: T[]): boolean
```
It returns `true`, if all members of array `list` returns `false`, when applied as argument to `predicate` function.
Try this R.none example in Rambda REPL
All TypeScript definitions
```typescript
none(predicate: (x: T) => boolean, list: T[]): boolean;
none(predicate: (x: T) => boolean): (list: T[]) => boolean;
```
R.none source
```javascript
export function none(predicate, list){
if (arguments.length === 1) return _list => none(predicate, _list)
for (let i = 0; i < list.length; i++){
if (predicate(list[ i ])) return false
}
return true
}
```
Tests
```javascript
import { none } from './none.js'
const isEven = n => n % 2 === 0
test('when true', () => {
expect(none(isEven, [ 1, 3, 5, 7 ])).toBeTrue()
})
test('when false curried', () => {
expect(none(input => input > 1, [ 1, 2, 3 ])).toBeFalse()
})
```
TypeScript test
```typescript
import {none} from 'rambda'
describe('R.none', () => {
it('happy', () => {
const result = none(
x => {
x // $ExpectType number
return x > 0
},
[1, 2, 3]
)
result // $ExpectType boolean
})
it('curried needs a type', () => {
const result = none(x => {
x // $ExpectType number
return x > 0
})([1, 2, 3])
result // $ExpectType boolean
})
})
```
[](#none)
### not
```typescript
not(input: any): boolean
```
It returns a boolean negated version of `input`.
Try this R.not example in Rambda REPL
All TypeScript definitions
```typescript
not(input: any): boolean;
```
R.not source
```javascript
export function not(input){
return !input
}
```
Tests
```javascript
import { not } from './not.js'
test('not', () => {
expect(not(false)).toBeTrue()
expect(not(true)).toBeFalse()
expect(not(0)).toBeTrue()
expect(not(1)).toBeFalse()
})
```
TypeScript test
```typescript
import {not} from 'rambda'
describe('R.not', () => {
it('happy', () => {
const result = not(4)
result // $ExpectType boolean
})
})
```
[](#not)
### nth
```typescript
nth(index: number, input: string): string
```
Curried version of `input[index]`.
Try this R.nth example in Rambda REPL
All TypeScript definitions
```typescript
nth(index: number, input: string): string;
nth(index: number, input: T[]): T | undefined;
nth(n: number): {
(input: T[]): T | undefined;
(input: string): string;
};
```
R.nth source
```javascript
export function nth(index, input){
if (arguments.length === 1) return _input => nth(index, _input)
const idx = index < 0 ? input.length + index : index
return Object.prototype.toString.call(input) === '[object String]' ?
input.charAt(idx) :
input[ idx ]
}
```
Tests
```javascript
import { nth } from './nth.js'
test('happy', () => {
expect(nth(2, [ 1, 2, 3, 4 ])).toBe(3)
})
test('with curry', () => {
expect(nth(2)([ 1, 2, 3, 4 ])).toBe(3)
})
test('with string and correct index', () => {
expect(nth(2)('foo')).toBe('o')
})
test('with string and invalid index', () => {
expect(nth(20)('foo')).toBe('')
})
test('with negative index', () => {
expect(nth(-3)([ 1, 2, 3, 4 ])).toBe(2)
})
```
TypeScript test
```typescript
import {nth} from 'rambda'
const list = [1, 2, 3]
describe('R.nth', () => {
it('happy', () => {
const result = nth(4, list)
result // $ExpectType number | undefined
})
it('curried', () => {
const result = nth(1)(list)
result // $ExpectType number | undefined
})
})
describe('R.nth - string', () => {
const str = 'abc'
it('happy', () => {
const result = nth(4, str)
result // $ExpectType string
})
it('curried', () => {
const result = nth(1)(str)
result // $ExpectType string
})
})
```
[](#nth)
### objOf
It creates an object with a single key-value pair.
Try this R.objOf example in Rambda REPL
[](#objOf)
### of
```typescript
of(x: T): T[]
```
Try this R.of example in Rambda REPL
All TypeScript definitions
```typescript
of(x: T): T[];
```
R.of source
```javascript
export function of(value){
return [ value ]
}
```
Tests
```javascript
import { of } from './of.js'
test('happy', () => {
expect(of(3)).toEqual([ 3 ])
expect(of(null)).toEqual([ null ])
})
```
TypeScript test
```typescript
import {of} from 'rambda'
const list = [1, 2, 3]
describe('R.of', () => {
it('happy', () => {
const result = of(4)
result // $ExpectType number[]
})
it('curried', () => {
const result = of(list)
result // $ExpectType number[][]
})
})
```
[](#of)
### omit
```typescript
omit(propsToOmit: K[], obj: T): Omit
```
It returns a partial copy of an `obj` without `propsToOmit` properties.
Try this R.omit example in Rambda REPL
All TypeScript definitions
```typescript
omit(propsToOmit: K[], obj: T): Omit;
omit(propsToOmit: K[]): (obj: T) => Omit;
omit(propsToOmit: string, obj: T): U;
omit(propsToOmit: string): (obj: T) => U;
omit(propsToOmit: string, obj: object): T;
omit(propsToOmit: string): (obj: object) => T;
```
R.omit source
```javascript
import { createPath } from './_internals/createPath.js'
import { includes } from './_internals/includes.js'
export function omit(propsToOmit, obj){
if (arguments.length === 1) return _obj => omit(propsToOmit, _obj)
if (obj === null || obj === undefined)
return undefined
const propsToOmitValue = createPath(propsToOmit, ',')
const willReturn = {}
for (const key in obj)
if (!includes(key, propsToOmitValue))
willReturn[ key ] = obj[ key ]
return willReturn
}
```
Tests
```javascript
import { omit } from './omit.js'
test('with string as condition', () => {
const obj = {
a : 1,
b : 2,
c : 3,
}
const result = omit('a,c', obj)
const resultCurry = omit('a,c')(obj)
const expectedResult = { b : 2 }
expect(result).toEqual(expectedResult)
expect(resultCurry).toEqual(expectedResult)
})
test.only('with number as property to omit', () => {
const obj = {
1 : 1,
b : 2,
}
const result = omit([ 1 ], obj)
expect(result).toEqual({ b : 2 })
})
test('with null', () => {
expect(omit('a,b', null)).toBeUndefined()
})
test('happy', () => {
expect(omit([ 'a', 'c' ])({
a : 'foo',
b : 'bar',
c : 'baz',
})).toEqual({ b : 'bar' })
})
```
TypeScript test
```typescript
import {omit} from 'rambda'
describe('R.omit with array as props input', () => {
it('allow Typescript to infer object type', () => {
const input = {a: 'foo', b: 2, c: 3, d: 4}
const result = omit(['b,c'], input)
result.a // $ExpectType string
result.d // $ExpectType number
const curriedResult = omit(['a,c'], input)
curriedResult.a // $ExpectType string
curriedResult.d // $ExpectType number
})
it('declare type of input object', () => {
interface Input {
a: string,
b: number,
c: number,
d: number,
}
const input: Input = {a: 'foo', b: 2, c: 3, d: 4}
const result = omit(['b,c'], input)
result // $ExpectType Omit
result.a // $ExpectType string
result.d // $ExpectType number
const curriedResult = omit(['a,c'], input)
curriedResult.a // $ExpectType string
curriedResult.d // $ExpectType number
})
})
describe('R.omit with string as props input', () => {
interface Output {
b: number,
d: number,
}
it('explicitly declare output', () => {
const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4})
result // $ExpectType Output
result.b // $ExpectType number
const curriedResult = omit('a,c')({a: 1, b: 2, c: 3, d: 4})
curriedResult.b // $ExpectType number
})
it('explicitly declare input and output', () => {
interface Input {
a: number,
b: number,
c: number,
d: number,
}
const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4})
result // $ExpectType Output
result.b // $ExpectType number
const curriedResult = omit('a,c')({
a: 1,
b: 2,
c: 3,
d: 4,
})
curriedResult.b // $ExpectType number
})
it('without passing type', () => {
const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4})
result // $ExpectType unknown
})
})
```
[](#omit)
### on
It passes the two inputs through `unaryFn` and then the results are passed as inputs the the `binaryFn` to receive the final result(`binaryFn(unaryFn(FIRST_INPUT), unaryFn(SECOND_INPUT))`).
This method is also known as P combinator.
Try this R.on example in Rambda REPL
[](#on)
### once
```typescript
once(func: T): T
```
It returns a function, which invokes only once `fn` function.
Try this R.once example in Rambda REPL
All TypeScript definitions
```typescript
once(func: T): T;
```
R.once source
```javascript
import { curry } from './curry.js'
function onceFn(fn, context){
let result
return function (){
if (fn){
result = fn.apply(context || this, arguments)
fn = null
}
return result
}
}
export function once(fn, context){
if (arguments.length === 1){
const wrap = onceFn(fn, context)
return curry(wrap)
}
return onceFn(fn, context)
}
```
Tests
```javascript
import { once } from './once.js'
test('with counter', () => {
let counter = 0
const runOnce = once(x => {
counter++
return x + 2
})
expect(runOnce(1)).toBe(3)
runOnce(1)
runOnce(1)
runOnce(1)
expect(counter).toBe(1)
})
test('happy path', () => {
const addOneOnce = once((
a, b, c
) => a + b + c, 1)
expect(addOneOnce(
10, 20, 30
)).toBe(60)
expect(addOneOnce(40)).toBe(60)
})
```
TypeScript test
```typescript
import {once} from 'rambda'
describe('R.once', () => {
it('happy', () => {
const runOnce = once((x: number) => {
return x + 2
})
const result = runOnce(1)
result // $ExpectType number
})
})
```
[](#once)
### or
Logical OR
Try this R.or example in Rambda REPL
[](#or)
### over
```typescript
over(lens: Lens): {
(fn: (a: A) => A): (value: S) => S
```
It returns a copied **Object** or **Array** with modified value received by applying function `fn` to `lens` focus.
Try this R.over example in Rambda REPL
All TypeScript definitions
```typescript
over(lens: Lens): {
(fn: (a: A) => A): (value: S) => S;
(fn: (a: A) => A, value: S): S;
};
over(lens: Lens, fn: (a: A) => A): (value: S) => S;
over(lens: Lens, fn: (a: A) => A, value: S): S;
```
R.over source
```javascript
import { curry } from './curry.js'
const Identity = x => ({
x,
map : fn => Identity(fn(x)),
})
function overFn(
lens, fn, object
){
return lens(x => Identity(fn(x)))(object).x
}
export const over = curry(overFn)
```
Tests
```javascript
import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { lensIndex } from './lensIndex.js'
import { lensPath } from './lensPath.js'
import { over } from './over.js'
import { prop } from './prop.js'
import { toUpper } from './toUpper.js'
const testObject = {
foo : 'bar',
baz : {
a : 'x',
b : 'y',
},
}
test('assoc lens', () => {
const assocLens = lens(prop('foo'), assoc('foo'))
const result = over(
assocLens, toUpper, testObject
)
const expected = {
...testObject,
foo : 'BAR',
}
expect(result).toEqual(expected)
})
test('path lens', () => {
const pathLens = lensPath('baz.a')
const result = over(
pathLens, toUpper, testObject
)
const expected = {
...testObject,
baz : {
a : 'X',
b : 'y',
},
}
expect(result).toEqual(expected)
})
test('index lens', () => {
const indexLens = lensIndex(0)
const result = over(indexLens, toUpper)([ 'foo', 'bar' ])
expect(result).toEqual([ 'FOO', 'bar' ])
})
```
[](#over)
### partial
```typescript
partial(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T
```
It is very similar to `R.curry`, but you can pass initial arguments when you create the curried function.
`R.partial` will keep returning a function until all the arguments that the function `fn` expects are passed.
The name comes from the fact that you partially inject the inputs.
Try this R.partial example in Rambda REPL
All TypeScript definitions
```typescript
partial(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T;
partial(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0, V1]): (x2: V2) => T;
partial(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0]): (x1: V1, x2: V2) => T;
partial(
fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T,
args: [V0, V1, V2],
): (x2: V3) => T;
partial(
fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T,
args: [V0, V1],
): (x2: V2, x3: V3) => T;
partial(
fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T,
args: [V0],
): (x1: V1, x2: V2, x3: V3) => T;
partial(fn: (...a: any[]) => T, args: any[]): (...a: any[]) => T;
```
R.partial source
```javascript
import { isArray } from './_internals/isArray.js'
export function partial(fn, ...args){
const len = fn.length
// If a single array argument is given, those are the args (a la Ramda).
// Otherwise, the variadic arguments are the args.
const argList = args.length === 1 && isArray(args[0]) ? args[0] : args
return (...rest) => {
if (argList.length + rest.length >= len){
return fn(...argList, ...rest)
}
return partial(fn, ...[ ...argList, ...rest ])
}
}
```
Tests
```javascript
import { partial } from './partial.js'
import { type } from './type.js'
const greet = (
salutation, title, firstName, lastName
) =>
[salutation, title, firstName, lastName]
test('happy', () => {
const canPassAnyNumberOfArguments = partial(
greet, 'Hello', 'Ms.'
)
const fn = canPassAnyNumberOfArguments('foo')
const sayHello = partial(greet, [ 'Hello' ])
const sayHelloRamda = partial(sayHello, [ 'Ms.' ])
expect(type(fn)).toBe('Function')
expect(fn('bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
expect(sayHelloRamda('foo', 'bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
})
test('extra arguments are ignored', () => {
const canPassAnyNumberOfArguments = partial(
greet, 'Hello', 'Ms.'
)
const fn = canPassAnyNumberOfArguments('foo')
expect(type(fn)).toBe('Function')
expect(fn(
'bar', 1, 2
)).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])
})
test('when array is input', () => {
const fooFn = (
a, b, c, d
) => ({
a,
b,
c,
d,
})
const barFn = partial(
fooFn, [ 1, 2 ], []
)
expect(barFn(1, 2)).toEqual({
a : [ 1, 2 ],
b : [],
c : 1,
d : 2,
})
})
test('ramda spec', () => {
const sayHello = partial(greet, 'Hello')
const sayHelloToMs = partial(sayHello, 'Ms.')
expect(sayHelloToMs('Jane', 'Jones')).toStrictEqual(['Hello', 'Ms.', 'Jane', 'Jones'])
})
```
TypeScript test
```typescript
import {partial} from 'rambda'
describe('R.partial', () => {
it('happy', () => {
function fn(
aString: string,
aNumber: number,
aBoolean: boolean,
aNull: null
) {
return {aString, aNumber, aBoolean, aNull}
}
// @ts-expect-error
partial(fn, 1)
const fn1 = partial(fn, ['a'])
partial(fn1, ['b'])
const fn2 = partial(fn1, [2])
const result = fn2(true, null)
result // $ExpectType { aString: string; aNumber: number; aBoolean: boolean; aNull: null; }
})
})
```
[](#partial)
### partialObject
```typescript
partialObject(
fn: (input: Input) => Output,
partialInput: PartialInput,
): (input: Pick>) => Output
```
`R.partialObject` is a curry helper designed specifically for functions accepting object as a single argument.
Initially the function knows only a part from the whole input object and then `R.partialObject` helps in preparing the function for the second part, when it receives the rest of the input.
Try this R.partialObject example in Rambda REPL
All TypeScript definitions
```typescript
partialObject(
fn: (input: Input) => Output,
partialInput: PartialInput,
): (input: Pick>) => Output;
```
R.partialObject source
```javascript
import { mergeDeepRight } from './mergeDeepRight.js'
export function partialObject(fn, input){
return nextInput => fn(mergeDeepRight(nextInput, input))
}
```
Tests
```javascript
import { delay } from './delay.js'
import { partialObject } from './partialObject.js'
import { type } from './type.js'
test('with plain function', () => {
const fn = ({ a, b, c }) => a + b + c
const curried = partialObject(fn, { a : 1 })
expect(type(curried)).toBe('Function')
expect(curried({
b : 2,
c : 3,
})).toBe(6)
})
test('with function that throws an error', () => {
const fn = ({ a, b, c }) => {
throw new Error('foo')
}
const curried = partialObject(fn, { a : 1 })
expect(type(curried)).toBe('Function')
expect(() =>
curried({
b : 2,
c : 3,
})).toThrowErrorMatchingInlineSnapshot('"foo"')
})
test('with async', async () => {
const fn = async ({ a, b, c }) => {
await delay(100)
return a + b + c
}
const curried = partialObject(fn, { a : 1 })
const result = await curried({
b : 2,
c : 3,
})
expect(result).toBe(6)
})
test('async function throwing an error', async () => {
const fn = async ({ a, b, c }) => {
await delay(100)
throw new Error('foo')
}
const curried = partialObject(fn, { a : 1 })
try {
await curried({
b : 2,
c : 3,
})
expect(true).toBeFalsy()
} catch (e){
expect(e.message).toBe('foo')
}
})
```
TypeScript test
```typescript
import {partialObject, delay} from 'rambda'
describe('R.partialObject', () => {
it('happy', () => {
interface Input {
a: number,
b: number,
c: string,
}
const fn = ({a, b, c}: Input) => a + b + c
const curried = partialObject(fn, {a: 1})
const result = curried({
b: 2,
c: 'foo',
})
result // $ExpectType string
})
it('asynchronous', async() => {
interface Input {
a: number,
b: number,
c: string,
}
const fn = async({a, b, c}: Input) => {
await delay(100)
return a + b + c
}
const curried = partialObject(fn, {a: 1})
const result = await curried({
b: 2,
c: 'foo',
})
result // $ExpectType string
})
})
```
[](#partialObject)
### partition
```typescript
partition(
predicate: Predicate,
input: T[]
): [T[], T[]]
```
It will return array of two objects/arrays according to `predicate` function. The first member holds all instances of `input` that pass the `predicate` function, while the second member - those who doesn't.
Try this R.partition example in Rambda REPL
All TypeScript definitions
```typescript
partition(
predicate: Predicate,
input: T[]
): [T[], T[]];
partition(
predicate: Predicate
): (input: T[]) => [T[], T[]];
partition(
predicate: (x: T, prop?: string) => boolean,
input: { [key: string]: T}
): [{ [key: string]: T}, { [key: string]: T}];
partition(
predicate: (x: T, prop?: string) => boolean
): (input: { [key: string]: T}) => [{ [key: string]: T}, { [key: string]: T}];
```
R.partition source
```javascript
import { isArray } from './_internals/isArray.js'
export function partitionObject(predicate, iterable){
const yes = {}
const no = {}
Object.entries(iterable).forEach(([ prop, value ]) => {
if (predicate(value, prop)){
yes[ prop ] = value
} else {
no[ prop ] = value
}
})
return [ yes, no ]
}
export function partitionArray(
predicate, list, indexed = false
){
const yes = []
const no = []
let counter = -1
while (counter++ < list.length - 1){
if (
indexed ? predicate(list[ counter ], counter) : predicate(list[ counter ])
){
yes.push(list[ counter ])
} else {
no.push(list[ counter ])
}
}
return [ yes, no ]
}
export function partition(predicate, iterable){
if (arguments.length === 1){
return listHolder => partition(predicate, listHolder)
}
if (!isArray(iterable)) return partitionObject(predicate, iterable)
return partitionArray(predicate, iterable)
}
```
Tests
```javascript
import { partition } from './partition.js'
test('with array', () => {
const predicate = x => x > 2
const list = [ 1, 2, 3, 4 ]
const result = partition(predicate, list)
const expectedResult = [
[ 3, 4 ],
[ 1, 2 ],
]
expect(result).toEqual(expectedResult)
})
test('with object', () => {
const predicate = (value, prop) => {
expect(typeof prop).toBe('string')
return value > 2
}
const hash = {
a : 1,
b : 2,
c : 3,
d : 4,
}
const result = partition(predicate)(hash)
const expectedResult = [
{
c : 3,
d : 4,
},
{
a : 1,
b : 2,
},
]
expect(result).toEqual(expectedResult)
})
test('readme example', () => {
const list = [ 1, 2, 3 ]
const obj = {
a : 1,
b : 2,
c : 3,
}
const predicate = x => x > 2
const result = [ partition(predicate, list), partition(predicate, obj) ]
const expected = [
[ [ 3 ], [ 1, 2 ] ],
[
{ c : 3 },
{
a : 1,
b : 2,
},
],
]
expect(result).toEqual(expected)
})
```
TypeScript test
```typescript
import {partition} from 'rambda'
describe('R.partition', () => {
it('with array', () => {
const predicate = (x: number) => {
return x > 2
}
const list = [1, 2, 3, 4]
const result = partition(predicate, list)
const curriedResult = partition(predicate)(list)
result // $ExpectType [number[], number[]]
curriedResult // $ExpectType [number[], number[]]
})
/*
revert to old version of `dtslint` and `R.partition` typing
as there is diff between VSCode types(correct) and dtslint(incorrect)
it('with object', () => {
const predicate = (value: number, prop?: string) => {
return value > 2
}
const hash = {
a: 1,
b: 2,
c: 3,
d: 4,
}
const result = partition(predicate, hash)
const curriedResult = partition(predicate)(hash)
result[0] // $xExpectType { [key: string]: number; }
result[1] // $xExpectType { [key: string]: number; }
curriedResult[0] // $xExpectType { [key: string]: number; }
curriedResult[1] // $xExpectType { [key: string]: number; }
})
*/
})
```
[](#partition)
### path
```typescript
path(path: [K0], obj: S): S[K0]
```
If `pathToSearch` is `'a.b'` then it will return `1` if `obj` is `{a:{b:1}}`.
It will return `undefined`, if such path is not found.
Try this R.path example in Rambda REPL
All TypeScript definitions
```typescript
path(path: [K0], obj: S): S[K0];
path(path: [K0, K1], obj: S): S[K0][K1];
path<
S,
K0 extends keyof S = keyof S,
K1 extends keyof S[K0] = keyof S[K0],
K2 extends keyof S[K0][K1] = keyof S[K0][K1]
>(path: [K0, K1, K2], obj: S): S[K0][K1][K2];
path<
S,
K0 extends keyof S = keyof S,
K1 extends keyof S[K0] = keyof S[K0],
K2 extends keyof S[K0][K1] = keyof S[K0][K1],
K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],
>(path: [K0, K1, K2, K3], obj: S): S[K0][K1][K2][K3];
path<
S,
K0 extends keyof S = keyof S,
K1 extends keyof S[K0] = keyof S[K0],
K2 extends keyof S[K0][K1] = keyof S[K0][K1],
K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],
K4 extends keyof S[K0][K1][K2][K3] = keyof S[K0][K1][K2][K3],
>(path: [K0, K1, K2, K3, K4], obj: S): S[K0][K1][K2][K3][K4];
path<
S,
K0 extends keyof S = keyof S,
K1 extends keyof S[K0] = keyof S[K0],
K2 extends keyof S[K0][K1] = keyof S[K0][K1],
K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],
K4 extends keyof S[K0][K1][K2][K3] = keyof S[K0][K1][K2][K3],
K5 extends keyof S[K0][K1][K2][K3][K4] = keyof S[K0][K1][K2][K3][K4],
>(path: [K0, K1, K2, K3, K4, K5], obj: S): S[K0][K1][K2][K3][K4][K5];
path(pathToSearch: string, obj: any): T | undefined;
path(pathToSearch: string): (obj: any) => T | undefined;
path(pathToSearch: RamdaPath): (obj: any) => T | undefined;
path(pathToSearch: RamdaPath, obj: any): T | undefined;
```
R.path source
```javascript
import { createPath } from './_internals/createPath.js'
export function pathFn(pathInput, obj){
let willReturn = obj
let counter = 0
const pathArrValue = createPath(pathInput)
while (counter < pathArrValue.length){
if (willReturn === null || willReturn === undefined){
return undefined
}
if (willReturn[ pathArrValue[ counter ] ] === null) return undefined
willReturn = willReturn[ pathArrValue[ counter ] ]
counter++
}
return willReturn
}
export function path(pathInput, obj){
if (arguments.length === 1) return _obj => path(pathInput, _obj)
if (obj === null || obj === undefined){
return undefined
}
return pathFn(pathInput, obj)
}
```
Tests
```javascript
import { path } from './path.js'
test('with array inside object', () => {
const obj = { a : { b : [ 1, { c : 1 } ] } }
expect(path('a.b.1.c', obj)).toBe(1)
})
test('works with undefined', () => {
const obj = { a : { b : { c : 1 } } }
expect(path('a.b.c.d.f', obj)).toBeUndefined()
expect(path('foo.babaz', undefined)).toBeUndefined()
expect(path('foo.babaz')(undefined)).toBeUndefined()
})
test('works with string instead of array', () => {
expect(path('foo.bar.baz')({ foo : { bar : { baz : 'yes' } } })).toBe('yes')
})
test('path', () => {
expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : { baz : 'yes' } } })).toBe('yes')
expect(path([ 'foo', 'bar', 'baz' ])(null)).toBeUndefined()
expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : 'baz' } })).toBeUndefined()
})
test('null is not a valid path', () => {
expect(path('audio_tracks', {
a : 1,
audio_tracks : null,
})).toBeUndefined()
})
```
TypeScript test
```typescript
import {path} from 'rambda'
const input = {a: {b: {c: true}}}
describe('R.path with string as path', () => {
it('without specified output type', () => {
// $ExpectType unknown
path('a.b.c', input)
// $ExpectType unknown
path('a.b.c')(input)
})
it('with specified output type', () => {
// $ExpectType boolean | undefined
path('a.b.c', input)
// $ExpectType boolean | undefined
path('a.b.c')(input)
})
})
describe('R.path with list as path', () => {
it('with array as path', () => {
// $ExpectType boolean
path(['a', 'b', 'c'], input)
// $ExpectType unknown
path(['a', 'b', 'c'])(input)
})
test('shallow property', () => {
// $ExpectType number
path(['a'], {a: 1})
// $ExpectType unknown
path(['b'], {a: 1})
})
test('deep property', () => {
const testObject = {a: {b: {c: {d: {e: {f: 1}}}}}}
const result = path(['a', 'b', 'c', 'd', 'e', 'f'], testObject)
// $ExpectType number
result
const curriedResult = path(['a', 'b', 'c', 'd', 'e', 'f'])(testObject)
// $ExpectType unknown
curriedResult
})
test('issue #668 - path is not correct', () => {
const object = {
is: {
a: 'path',
},
}
const result = path(['is', 'not', 'a'], object)
// $ExpectType unknown
result
const curriedResult = path(['is', 'not', 'a'])(object)
// $ExpectType unknown
curriedResult
})
})
```
[](#path)
### pathEq
```typescript
pathEq(pathToSearch: Path, target: any, input: any): boolean
```
It returns `true` if `pathToSearch` of `input` object is equal to `target` value.
`pathToSearch` is passed to `R.path`, which means that it can be either a string or an array. Also equality between `target` and the found value is determined by `R.equals`.
Try this R.pathEq example in Rambda REPL
All TypeScript definitions
```typescript
pathEq(pathToSearch: Path, target: any, input: any): boolean;
pathEq(pathToSearch: Path, target: any): (input: any) => boolean;
pathEq(pathToSearch: Path): (target: any) => (input: any) => boolean;
```
R.pathEq source
```javascript
import { curry } from './curry.js'
import { equals } from './equals.js'
import { path } from './path.js'
function pathEqFn(
pathToSearch, target, input
){
return equals(path(pathToSearch, input), target)
}
export const pathEq = curry(pathEqFn)
```
Tests
```javascript
import { pathEq } from './pathEq.js'
test('when true', () => {
const path = 'a.b'
const obj = { a : { b : { c : 1 } } }
const target = { c : 1 }
expect(pathEq(
path, target, obj
)).toBeTrue()
})
test('when false', () => {
const path = 'a.b'
const obj = { a : { b : 1 } }
const target = 2
expect(pathEq(path, target)(obj)).toBeFalse()
})
test('when wrong path', () => {
const path = 'foo.bar'
const obj = { a : { b : 1 } }
const target = 2
expect(pathEq(
path, target, obj
)).toBeFalse()
})
```
TypeScript test
```typescript
import {pathEq} from 'rambda'
describe('R.pathEq', () => {
it('with string path', () => {
const pathToSearch = 'a.b.c'
const input = {a: {b: {c: 1}}}
const target = {c: 1}
const result = pathEq(pathToSearch, input, target)
const curriedResult = pathEq(pathToSearch, input, target)
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
it('with array path', () => {
const pathToSearch = ['a', 'b', 'c']
const input = {a: {b: {c: 1}}}
const target = {c: 1}
const result = pathEq(pathToSearch, input, target)
const curriedResult = pathEq(pathToSearch, input, target)
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
})
describe('with ramda specs', () => {
const testPath = ['x', 0, 'y']
const testObj = {
x: [
{y: 2, z: 3},
{y: 4, z: 5},
],
}
const result1 = pathEq(testPath, 2, testObj)
const result2 = pathEq(testPath, 2)(testObj)
const result3 = pathEq(testPath)(2)(testObj)
result1 // $ExpectType boolean
result2 // $ExpectType boolean
result3 // $ExpectType boolean
})
```
[](#pathEq)
### pathOr
```typescript
pathOr(defaultValue: T, pathToSearch: Path, obj: any): T
```
It reads `obj` input and returns either `R.path(pathToSearch, Record)` result or `defaultValue` input.
Try this R.pathOr example in Rambda REPL
All TypeScript definitions
```typescript
pathOr(defaultValue: T, pathToSearch: Path, obj: any): T;
pathOr(defaultValue: T, pathToSearch: Path): (obj: any) => T;
pathOr(defaultValue: T): (pathToSearch: Path) => (obj: any) => T;
```
R.pathOr source
```javascript
import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'
import { path } from './path.js'
function pathOrFn(
defaultValue, pathInput, obj
){
return defaultTo(defaultValue, path(pathInput, obj))
}
export const pathOr = curry(pathOrFn)
```
Tests
```javascript
import { pathOr } from './pathOr.js'
test('with undefined', () => {
const result = pathOr(
'foo', 'x.y', { x : { y : 1 } }
)
expect(result).toBe(1)
})
test('with null', () => {
const result = pathOr(
'foo', 'x.y', null
)
expect(result).toBe('foo')
})
test('with NaN', () => {
const result = pathOr(
'foo', 'x.y', NaN
)
expect(result).toBe('foo')
})
test('curry case (x)(y)(z)', () => {
const result = pathOr('foo')('x.y.z')({ x : { y : { a : 1 } } })
expect(result).toBe('foo')
})
test('curry case (x)(y,z)', () => {
const result = pathOr('foo', 'x.y.z')({ x : { y : { a : 1 } } })
expect(result).toBe('foo')
})
test('curry case (x,y)(z)', () => {
const result = pathOr('foo')('x.y.z', { x : { y : { a : 1 } } })
expect(result).toBe('foo')
})
```
TypeScript test
```typescript
import {pathOr} from 'rambda'
describe('R.pathOr', () => {
it('with string path', () => {
const x = pathOr('foo', 'x.y', {x: {y: 'bar'}})
x // $ExpectType string
})
it('with array path', () => {
const x = pathOr('foo', ['x', 'y'], {x: {y: 'bar'}})
x // $ExpectType string
})
it('without passing type looks bad', () => {
const x = pathOr('foo', 'x.y', {x: {y: 'bar'}})
x // $ExpectType "foo"
})
it('curried', () => {
const x = pathOr('foo', 'x.y')({x: {y: 'bar'}})
x // $ExpectType string
})
})
```
[](#pathOr)
### paths
```typescript
paths(pathsToSearch: Path[], obj: Input): (T | undefined)[]
```
It loops over members of `pathsToSearch` as `singlePath` and returns the array produced by `R.path(singlePath, Record)`.
Because it calls `R.path`, then `singlePath` can be either string or a list.
Try this R.paths example in Rambda REPL
All TypeScript definitions
```typescript
paths(pathsToSearch: Path[], obj: Input): (T | undefined)[];
paths(pathsToSearch: Path[]): (obj: Input) => (T | undefined)[];
paths(pathsToSearch: Path[], obj: any): (T | undefined)[];
paths(pathsToSearch: Path[]): (obj: any) => (T | undefined)[];
```
R.paths source
```javascript
import { path } from './path.js'
export function paths(pathsToSearch, obj){
if (arguments.length === 1){
return _obj => paths(pathsToSearch, _obj)
}
return pathsToSearch.map(singlePath => path(singlePath, obj))
}
```
Tests
```javascript
import { paths } from './paths.js'
const obj = {
a : {
b : {
c : 1,
d : 2,
},
},
p : [ { q : 3 } ],
x : {
y : 'FOO',
z : [ [ {} ] ],
},
}
test('with string path + curry', () => {
const pathsInput = [ 'a.b.d', 'p.q' ]
const expected = [ 2, undefined ]
const result = paths(pathsInput, obj)
const curriedResult = paths(pathsInput)(obj)
expect(result).toEqual(expected)
expect(curriedResult).toEqual(expected)
})
test('with array path', () => {
const result = paths([
[ 'a', 'b', 'c' ],
[ 'x', 'y' ],
],
obj)
expect(result).toEqual([ 1, 'FOO' ])
})
test('takes a paths that contains indices into arrays', () => {
expect(paths([
[ 'p', 0, 'q' ],
[ 'x', 'z', 0, 0 ],
],
obj)).toEqual([ 3, {} ])
expect(paths([
[ 'p', 0, 'q' ],
[ 'x', 'z', 2, 1 ],
],
obj)).toEqual([ 3, undefined ])
})
test('gets a deep property\'s value from objects', () => {
expect(paths([ [ 'a', 'b' ] ], obj)).toEqual([ obj.a.b ])
expect(paths([ [ 'p', 0 ] ], obj)).toEqual([ obj.p[ 0 ] ])
})
test('returns undefined for items not found', () => {
expect(paths([ [ 'a', 'x', 'y' ] ], obj)).toEqual([ undefined ])
expect(paths([ [ 'p', 2 ] ], obj)).toEqual([ undefined ])
})
```
TypeScript test
```typescript
import {paths} from 'rambda'
interface Input {
a: number,
b: number,
c: number,
}
const input: Input = {a: 1, b: 2, c: 3}
describe('R.paths', () => {
it('with dot notation', () => {
const result = paths(['a.b.c', 'foo.bar'], input)
result // $ExpectType (number | undefined)[]
})
it('without type', () => {
const result = paths(['a.b.c', 'foo.bar'], input)
result // $ExpectType unknown[]
})
it('with array as path', () => {
const result = paths([['a', 'b', 'c'], ['foo.bar']], input)
result // $ExpectType (number | undefined)[]
})
it('curried', () => {
const result = paths([['a', 'b', 'c'], ['foo.bar']])(input)
result // $ExpectType (number | undefined)[]
})
})
```
[](#paths)
### pick
```typescript
pick(propsToPick: K[], input: T): Pick>>
```
It returns a partial copy of an `input` containing only `propsToPick` properties.
`input` can be either an object or an array.
String annotation of `propsToPick` is one of the differences between `Rambda` and `Ramda`.
Try this R.pick example in Rambda REPL
All TypeScript definitions
```typescript
pick(propsToPick: K[], input: T): Pick>>;
pick(propsToPick: K[]): (input: T) => Pick>>;
pick(propsToPick: string, input: T): U;
pick(propsToPick: string): (input: T) => U;
pick(propsToPick: string, input: object): T;
pick(propsToPick: string): (input: object) => T;
```
R.pick source
```javascript
import { createPath } from './_internals/createPath.js'
export function pick(propsToPick, input){
if (arguments.length === 1) return _input => pick(propsToPick, _input)
if (input === null || input === undefined){
return undefined
}
const keys = createPath(propsToPick, ',')
const willReturn = {}
let counter = 0
while (counter < keys.length){
if (keys[ counter ] in input){
willReturn[ keys[ counter ] ] = input[ keys[ counter ] ]
}
counter++
}
return willReturn
}
```
Tests
```javascript
import { pick } from './pick.js'
const obj = {
a : 1,
b : 2,
c : 3,
}
test('props to pick is a string', () => {
const result = pick('a,c', obj)
const resultCurry = pick('a,c')(obj)
const expectedResult = {
a : 1,
c : 3,
}
expect(result).toEqual(expectedResult)
expect(resultCurry).toEqual(expectedResult)
})
test('when prop is missing', () => {
const result = pick('a,d,f', obj)
expect(result).toEqual({ a : 1 })
})
test('with list indexes as props', () => {
const list = [ 1, 2, 3 ]
const expected = {
0 : 1,
2 : 3,
}
expect(pick([ 0, 2, 3 ], list)).toEqual(expected)
expect(pick('0,2,3', list)).toEqual(expected)
})
test('props to pick is an array', () => {
expect(pick([ 'a', 'c' ])({
a : 'foo',
b : 'bar',
c : 'baz',
})).toEqual({
a : 'foo',
c : 'baz',
})
expect(pick([ 'a', 'd', 'e', 'f' ])({
a : 'foo',
b : 'bar',
c : 'baz',
})).toEqual({ a : 'foo' })
expect(pick('a,d,e,f')(null)).toBeUndefined()
})
test('works with list as input and number as props - props to pick is an array', () => {
const result = pick([ 1, 2 ], [ 'a', 'b', 'c', 'd' ])
expect(result).toEqual({
1 : 'b',
2 : 'c',
})
})
test('works with list as input and number as props - props to pick is a string', () => {
const result = pick('1,2', [ 'a', 'b', 'c', 'd' ])
expect(result).toEqual({
1 : 'b',
2 : 'c',
})
})
test('with symbol', () => {
const symbolProp = Symbol('s')
expect(pick([ symbolProp ], { [ symbolProp ] : 'a' })).toMatchInlineSnapshot(`
{
Symbol(s): "a",
}
`)
})
```
TypeScript test
```typescript
import {pick} from 'rambda'
const input = {a: 'foo', b: 2, c: 3, d: 4}
describe('R.pick with array as props input', () => {
it('without passing type', () => {
const result = pick(['a', 'c'], input)
result.a // $ExpectType string
result.c // $ExpectType number
})
})
describe('R.pick with string as props input', () => {
interface Input {
a: string,
b: number,
c: number,
d: number,
}
interface Output {
a: string,
c: number,
}
it('explicitly declare output', () => {
const result = pick('a,c', input)
result // $ExpectType Output
result.a // $ExpectType string
result.c // $ExpectType number
const curriedResult = pick('a,c')(input)
curriedResult.a // $ExpectType string
})
it('explicitly declare input and output', () => {
const result = pick('a,c', input)
result // $ExpectType Output
result.a // $ExpectType string
const curriedResult = pick('a,c')(input)
curriedResult.a // $ExpectType string
})
it('without passing type', () => {
const result = pick('a,c', input)
result // $ExpectType unknown
})
})
```
[](#pick)
### pickAll
```typescript
pickAll(propsToPicks: K[], input: T): Pick
```
Same as `R.pick` but it won't skip the missing props, i.e. it will assign them to `undefined`.
Try this R.pickAll example in Rambda REPL
All TypeScript definitions
```typescript
pickAll(propsToPicks: K[], input: T): Pick;
pickAll(propsToPicks: string[], input: T): U;
pickAll(propsToPicks: string[]): (input: T) => U;
pickAll(propsToPick: string, input: T): U;
pickAll(propsToPick: string): (input: T) => U;
```
R.pickAll source
```javascript
import { createPath } from './_internals/createPath.js'
export function pickAll(propsToPick, obj){
if (arguments.length === 1) return _obj => pickAll(propsToPick, _obj)
if (obj === null || obj === undefined){
return undefined
}
const keysValue = createPath(propsToPick, ',')
const willReturn = {}
let counter = 0
while (counter < keysValue.length){
if (keysValue[ counter ] in obj){
willReturn[ keysValue[ counter ] ] = obj[ keysValue[ counter ] ]
} else {
willReturn[ keysValue[ counter ] ] = undefined
}
counter++
}
return willReturn
}
```
Tests
```javascript
import { pickAll } from './pickAll.js'
test('when input is undefined or null', () => {
expect(pickAll('a', null)).toBeUndefined()
expect(pickAll('a', undefined)).toBeUndefined()
})
test('with string as condition', () => {
const obj = {
a : 1,
b : 2,
c : 3,
}
const result = pickAll('a,c', obj)
const resultCurry = pickAll('a,c')(obj)
const expectedResult = {
a : 1,
b : undefined,
c : 3,
}
expect(result).toEqual(expectedResult)
expect(resultCurry).toEqual(expectedResult)
})
test('with array as condition', () => {
expect(pickAll([ 'a', 'b', 'c' ], {
a : 'foo',
c : 'baz',
})).toEqual({
a : 'foo',
b : undefined,
c : 'baz',
})
})
```
TypeScript test
```typescript
import {pickAll} from 'rambda'
interface Input {
a: string,
b: number,
c: number,
d: number,
}
interface Output {
a?: string,
c?: number,
}
const input = {a: 'foo', b: 2, c: 3, d: 4}
describe('R.pickAll with array as props input', () => {
it('without passing type', () => {
const result = pickAll(['a', 'c'], input)
result.a // $ExpectType string
result.c // $ExpectType number
})
it('without passing type + curry', () => {
const result = pickAll(['a', 'c'])(input)
result // $ExpectType unknown
})
it('explicitly passing types', () => {
const result = pickAll(['a', 'c'], input)
result.a // $ExpectType string | undefined
result.c // $ExpectType number | undefined
})
})
describe('R.pickAll with string as props input', () => {
it('without passing type', () => {
const result = pickAll('a,c', input)
result // $ExpectType unknown
})
it('without passing type + curry', () => {
const result = pickAll('a,c')(input)
result // $ExpectType unknown
})
it('explicitly passing types', () => {
const result = pickAll('a,c', input)
result.a // $ExpectType string | undefined
result.c // $ExpectType number | undefined
})
it('explicitly passing types + curry', () => {
const result = pickAll('a,c')(input)
result.a // $ExpectType string | undefined
result.c // $ExpectType number | undefined
})
})
```
[](#pickAll)
### pipe
It performs left-to-right function composition.
Try this R.pipe example in Rambda REPL
[](#pipe)
### pluck
```typescript
pluck(property: K, list: T[]): T[K][]
```
It returns list of the values of `property` taken from the all objects inside `list`.
Try this R.pluck example in Rambda REPL
All TypeScript definitions
```typescript
pluck(property: K, list: T[]): T[K][];
pluck(property: number, list: { [k: number]: T }[]): T[];
pluck
(property: P): (list: Record
[]) => T[];
pluck(property: number): (list: { [k: number]: T }[]) => T[];
```
R.pluck source
```javascript
import { map } from './map.js'
export function pluck(property, list){
if (arguments.length === 1) return _list => pluck(property, _list)
const willReturn = []
map(x => {
if (x[ property ] !== undefined){
willReturn.push(x[ property ])
}
}, list)
return willReturn
}
```
Tests
```javascript
import { pluck } from './pluck.js'
test('happy', () => {
expect(pluck('a')([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ 1, 2 ])
})
test('with undefined', () => {
expect(pluck(undefined)([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ ])
})
test('with number', () => {
const input = [
[ 1, 2 ],
[ 3, 4 ],
]
expect(pluck(0, input)).toEqual([ 1, 3 ])
})
```
TypeScript test
```typescript
import {pluck} from 'rambda'
describe('R.pluck', () => {
it('with object', () => {
interface ListMember {
a: number,
b: string,
}
const input: ListMember[] = [
{a: 1, b: 'foo'},
{a: 2, b: 'bar'},
]
const resultA = pluck('a', input)
const resultB = pluck('b')(input)
resultA // $ExpectType number[]
resultB // $ExpectType string[]
})
it('with array', () => {
const input = [
[1, 2],
[3, 4],
[5, 6],
]
const result = pluck(0, input)
const resultCurry = pluck(0)(input)
result // $ExpectType number[]
resultCurry // $ExpectType number[]
})
})
```
[](#pluck)
### prepend
```typescript
prepend(xToPrepend: T, iterable: T[]): T[]
```
It adds element `x` at the beginning of `list`.
Try this R.prepend example in Rambda REPL
All TypeScript definitions
```typescript
prepend(xToPrepend: T, iterable: T[]): T[];
prepend(xToPrepend: T, iterable: IsFirstSubtypeOfSecond[]) : U[];
prepend(xToPrepend: T): (iterable: IsFirstSubtypeOfSecond[]) => U[];
prepend(xToPrepend: T): (iterable: T[]) => T[];
```
R.prepend source
```javascript
export function prepend(x, input){
if (arguments.length === 1) return _input => prepend(x, _input)
if (typeof input === 'string') return [ x ].concat(input.split(''))
return [ x ].concat(input)
}
```
Tests
```javascript
import { prepend } from './prepend.js'
test('happy', () => {
expect(prepend('yes', [ 'foo', 'bar', 'baz' ])).toEqual([
'yes',
'foo',
'bar',
'baz',
])
})
test('with empty list', () => {
expect(prepend('foo')([])).toEqual([ 'foo' ])
})
test('with string instead of array', () => {
expect(prepend('foo')('bar')).toEqual([ 'foo', 'b', 'a', 'r' ])
})
```
[](#prepend)
### product
```typescript
product(list: number[]): number
```
Try this R.product example in Rambda REPL
All TypeScript definitions
```typescript
product(list: number[]): number;
```
R.product source
```javascript
import { multiply } from './multiply.js'
import { reduce } from './reduce.js'
export const product = reduce(multiply, 1)
```
Tests
```javascript
import { product } from './product.js'
test('happy', () => {
expect(product([ 2, 3, 4 ])).toBe(24)
})
test('bad input', () => {
expect(product([ null ])).toBe(0)
expect(product([])).toBe(1)
})
```
TypeScript test
```typescript
import {product} from 'rambda'
describe('R.product', () => {
it('happy', () => {
const result = product([1, 2, 3])
result // $ExpectType number
})
})
```
[](#product)
### prop
```typescript
prop<_, P extends keyof never, T>(p: P, value: T): Prop
```
It returns the value of property `propToFind` in `obj`.
If there is no such property, it returns `undefined`.
Try this R.prop example in Rambda REPL
All TypeScript definitions
```typescript
prop<_, P extends keyof never, T>(p: P, value: T): Prop;
prop(p: keyof never, value: unknown): V;
prop<_, P extends keyof never>(p: P): (value: T) => Prop;
prop(p: keyof never): (value: unknown) => V;
```
R.prop source
```javascript
export function propFn(searchProperty, obj){
if (!obj) return undefined
return obj[ searchProperty ]
}
export function prop(searchProperty, obj){
if (arguments.length === 1) return _obj => prop(searchProperty, _obj)
return propFn(searchProperty, obj)
}
```
Tests
```javascript
import { prop } from './prop.js'
test('prop', () => {
expect(prop('foo')({ foo : 'baz' })).toBe('baz')
expect(prop('bar')({ foo : 'baz' })).toBeUndefined()
expect(prop('bar')(null)).toBeUndefined()
})
```
TypeScript test
```typescript
import {prop} from 'rambda'
describe('R.prop', () => {
interface Foo {
a: number,
b: string,
c?: number,
}
const obj: Foo = {a: 1, b: 'foo'}
it('issue #553', () => {
const result = {
a: prop('a', obj),
b: prop('b', obj),
c: prop('c', obj),
}
const curriedResult = {
a: prop('a')(obj),
b: prop('b')(obj),
c: prop('c')(obj),
}
result // $ExpectType { a: number; b: string; c: number | undefined; }
curriedResult // $ExpectType { a: number; b: string; c: number | undefined; }
})
})
describe('with number as prop', () => {
const list = [1, 2, 3]
const index = 1
it('happy', () => {
const result = prop(index, list)
result // $ExpectType number
})
it('curried require explicit type', () => {
const result = prop(index)(list)
result // $ExpectType number
})
})
```
[](#prop)
### propEq
```typescript
propEq(valueToMatch: any, propToFind: K, obj: Record): boolean
```
It returns true if `obj` has property `propToFind` and its value is equal to `valueToMatch`.
Try this R.propEq example in Rambda REPL
All TypeScript definitions
```typescript
propEq(valueToMatch: any, propToFind: K, obj: Record): boolean;
propEq(valueToMatch: any, propToFind: K): (obj: Record) => boolean;
propEq(valueToMatch: any): {
(propToFind: K, obj: Record): boolean;
(propToFind: K): (obj: Record) => boolean;
};
```
R.propEq source
```javascript
import { curry } from './curry.js'
import { equals } from './equals.js'
import { prop } from './prop.js'
function propEqFn(
valueToMatch, propToFind, obj
){
if (!obj) return false
return equals(valueToMatch, prop(propToFind, obj))
}
export const propEq = curry(propEqFn)
```
Tests
```javascript
import { BAR, FOO } from './_internals/testUtils.js'
import { propEq } from './propEq.js'
test('happy', () => {
const obj = { [ FOO ] : BAR }
expect(propEq(BAR, FOO)(obj)).toBeTrue()
expect(propEq(1, FOO)(obj)).toBeFalse()
expect(propEq(1)(FOO)(obj)).toBeFalse()
expect(propEq(
1, 1, null
)).toBeFalse()
})
test('returns false if called with a null or undefined object', () => {
expect(propEq(
'name', 'Abby', null
)).toBeFalse()
expect(propEq(
'name', 'Abby', undefined
)).toBeFalse()
})
```
TypeScript test
```typescript
import {propEq} from 'rambda'
const property = 'foo'
const numberProperty = 1
const value = 'bar'
const obj = {[property]: value}
const objWithNumberIndex = {[numberProperty]: value}
describe('R.propEq', () => {
it('happy', () => {
const result = propEq(value, property, obj)
result // $ExpectType boolean
})
it('number is property', () => {
const result = propEq(value, 1, objWithNumberIndex)
result // $ExpectType boolean
})
it('with optional property', () => {
interface MyType {
optional?: string | number,
}
const myObject: MyType = {}
const valueToFind = '1111'
// @ts-expect-error
propEq(valueToFind, 'optional', myObject)
})
it('imported from @types/ramda', () => {
interface A {
foo: string | null,
}
const obj: A = {
foo: 'bar',
}
const value = ''
const result = propEq(value, 'foo')(obj)
result // $ExpectType boolean
// @ts-expect-error
propEq(value, 'bar')(obj)
})
})
```
[](#propEq)
### propIs
```typescript
propIs(type: C, name: K, obj: any): obj is Record>
```
It returns `true` if `property` of `obj` is from `target` type.
Try this R.propIs example in Rambda REPL
All TypeScript definitions
```typescript
propIs(type: C, name: K, obj: any): obj is Record>;
propIs(type: C, name: K, obj: any): obj is Record>;
propIs(type: C, name: K): (obj: any) => obj is Record>;
propIs(type: C, name: K): (obj: any) => obj is Record>;
propIs(type: C): {
(name: K, obj: any): obj is Record>;
(name: K): (obj: any) => obj is Record>;
};
```
R.propIs source
```javascript
import { curry } from './curry.js'
import { is } from './is.js'
function propIsFn(
targetPrototype, property, obj
){
return is(targetPrototype, obj[ property ])
}
export const propIs = curry(propIsFn)
```
Tests
```javascript
import { propIs } from './propIs.js'
const obj = {
a : 1,
b : 'foo',
}
test('when true', () => {
expect(propIs(
Number, 'a', obj
)).toBeTrue()
expect(propIs(
String, 'b', obj
)).toBeTrue()
})
test('when false', () => {
expect(propIs(
String, 'a', obj
)).toBeFalse()
expect(propIs(
Number, 'b', obj
)).toBeFalse()
})
```
TypeScript test
```typescript
import {propIs} from 'rambda'
const property = 'a'
const obj = {a: 1}
describe('R.propIs', () => {
it('happy', () => {
const result = propIs(Number, property, obj)
result // $ExpectType boolean
})
it('curried', () => {
const result = propIs(Number, property)(obj)
result // $ExpectType boolean
})
})
```
[](#propIs)
### propOr
```typescript
propOr(defaultValue: T, property: P, obj: Partial> | undefined): T
```
It returns either `defaultValue` or the value of `property` in `obj`.
Try this R.propOr example in Rambda REPL
All TypeScript definitions
```typescript
propOr(defaultValue: T, property: P, obj: Partial> | undefined): T;
propOr(defaultValue: T, property: P): (obj: Partial> | undefined) => T;
propOr(defaultValue: T): {
(property: P, obj: Partial> | undefined): T;
(property: P): (obj: Partial> | undefined) => T;
}
```
R.propOr source
```javascript
import { curry } from './curry.js'
import { defaultTo } from './defaultTo.js'
function propOrFn(
defaultValue, property, obj
){
if (!obj) return defaultValue
return defaultTo(defaultValue, obj[ property ])
}
export const propOr = curry(propOrFn)
```
Tests
```javascript
import { propOr } from './propOr.js'
test('propOr (result)', () => {
const obj = { a : 1 }
expect(propOr(
'default', 'a', obj
)).toBe(1)
expect(propOr(
'default', 'notExist', obj
)).toBe('default')
expect(propOr(
'default', 'notExist', null
)).toBe('default')
})
test('propOr (currying)', () => {
const obj = { a : 1 }
expect(propOr('default')('a', obj)).toBe(1)
expect(propOr('default', 'a')(obj)).toBe(1)
expect(propOr('default')('notExist', obj)).toBe('default')
expect(propOr('default', 'notExist')(obj)).toBe('default')
})
```
TypeScript test
```typescript
import {propOr} from 'rambda'
const obj = {foo: 'bar'}
const property = 'foo'
const fallback = 'fallback'
describe('R.propOr', () => {
it('happy', () => {
const result = propOr(fallback, property, obj)
result // $ExpectType string
})
it('curry 1', () => {
const result = propOr(fallback)(property, obj)
result // $ExpectType string
})
it('curry 2', () => {
const result = propOr(fallback, property)(obj)
result // $ExpectType string
})
it('curry 3', () => {
const result = propOr(fallback)(property)(obj)
result // $ExpectType string
})
})
```
[](#propOr)
### props
```typescript
props
(propsToPick: P[], obj: Record
): T[]
```
It takes list with properties `propsToPick` and returns a list with property values in `obj`.
Try this R.props example in Rambda REPL
All TypeScript definitions
```typescript
props
(propsToPick: P[], obj: Record
): T[];
props
(propsToPick: P[]): (obj: Record
) => T[];
props
(propsToPick: P[]): (obj: Record
) => T[];
```
R.props source
```javascript
import { isArray } from './_internals/isArray.js'
import { mapArray } from './map.js'
export function props(propsToPick, obj){
if (arguments.length === 1){
return _obj => props(propsToPick, _obj)
}
if (!isArray(propsToPick)){
throw new Error('propsToPick is not a list')
}
return mapArray(prop => obj[ prop ], propsToPick)
}
```
Tests
```javascript
import { props } from './props.js'
const obj = {
a : 1,
b : 2,
}
const propsToPick = [ 'a', 'c' ]
test('happy', () => {
const result = props(propsToPick, obj)
expect(result).toEqual([ 1, undefined ])
})
test('curried', () => {
const result = props(propsToPick)(obj)
expect(result).toEqual([ 1, undefined ])
})
test('wrong input', () => {
expect(() => props(null)(obj)).toThrowErrorMatchingInlineSnapshot('"propsToPick is not a list"')
})
```
TypeScript test
```typescript
import {props} from 'rambda'
const obj = {a: 1, b: 2}
describe('R.props', () => {
it('happy', () => {
const result = props(['a', 'b'], obj)
result // $ExpectType number[]
})
it('curried', () => {
const result = props(['a', 'b'])(obj)
result // $ExpectType number[]
})
})
```
[](#props)
### propSatisfies
```typescript
propSatisfies(predicate: Predicate, property: string, obj: Record): boolean
```
It returns `true` if the object property satisfies a given predicate.
Try this R.propSatisfies example in Rambda REPL
All TypeScript definitions
```typescript
propSatisfies(predicate: Predicate, property: string, obj: Record): boolean;
propSatisfies(predicate: Predicate, property: string): (obj: Record) => boolean;
```
R.propSatisfies source
```javascript
import { curry } from './curry.js'
import { prop } from './prop.js'
function propSatisfiesFn(
predicate, property, obj
){
return predicate(prop(property, obj))
}
export const propSatisfies = curry(propSatisfiesFn)
```
Tests
```javascript
import { propSatisfies } from './propSatisfies.js'
const obj = { a : 1 }
test('when true', () => {
expect(propSatisfies(
x => x > 0, 'a', obj
)).toBeTrue()
})
test('when false', () => {
expect(propSatisfies(x => x < 0, 'a')(obj)).toBeFalse()
})
```
TypeScript test
```typescript
import {propSatisfies} from 'rambda'
const obj = {a: 1}
describe('R.propSatisfies', () => {
it('happy', () => {
const result = propSatisfies(x => x > 0, 'a', obj)
result // $ExpectType boolean
})
it('curried requires explicit type', () => {
const result = propSatisfies(x => x > 0, 'a')(obj)
result // $ExpectType boolean
})
})
```
[](#propSatisfies)
### range
```typescript
range(startInclusive: number, endExclusive: number): number[]
```
It returns list of numbers between `startInclusive` to `endExclusive` markers.
Try this R.range example in Rambda REPL
All TypeScript definitions
```typescript
range(startInclusive: number, endExclusive: number): number[];
range(startInclusive: number): (endExclusive: number) => number[];
```
R.range source
```javascript
export function range(start, end){
if (arguments.length === 1) return _end => range(start, _end)
if (Number.isNaN(Number(start)) || Number.isNaN(Number(end))){
throw new TypeError('Both arguments to range must be numbers')
}
if (end < start) return []
const len = end - start
const willReturn = Array(len)
for (let i = 0; i < len; i++){
willReturn[ i ] = start + i
}
return willReturn
}
```
Tests
```javascript
import { range } from './range.js'
test('happy', () => {
expect(range(0, 10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})
test('end range is bigger than start range', () => {
expect(range(7, 3)).toEqual([])
expect(range(5, 5)).toEqual([])
})
test('with bad input', () => {
const throwMessage = 'Both arguments to range must be numbers'
expect(() => range('a', 6)).toThrowWithMessage(Error, throwMessage)
expect(() => range(6, 'z')).toThrowWithMessage(Error, throwMessage)
})
test('curry', () => {
expect(range(0)(10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])
})
```
TypeScript test
```typescript
import {range} from 'rambda'
describe('R.range', () => {
it('happy', () => {
const result = range(1, 4)
result // $ExpectType number[]
})
it('curried', () => {
const result = range(1)(4)
result // $ExpectType number[]
})
})
```
[](#range)
### reduce
Try this R.reduce example in Rambda REPL
[](#reduce)
### reduceBy
Try this R.reduceBy example in Rambda REPL
[](#reduceBy)
### reject
```typescript
reject(predicate: Predicate, list: T[]): T[]
```
It has the opposite effect of `R.filter`.
Try this R.reject example in Rambda REPL
All TypeScript definitions
```typescript
reject(predicate: Predicate, list: T[]): T[];
reject(predicate: Predicate): (list: T[]) => T[];
reject(predicate: Predicate, obj: Dictionary): Dictionary;
reject(predicate: Predicate): (obj: Dictionary) => Dictionary;
```
R.reject source
```javascript
import { filter } from './filter.js'
export function reject(predicate, list){
if (arguments.length === 1) return _list => reject(predicate, _list)
return filter(x => !predicate(x), list)
}
```
Tests
```javascript
import { reject } from './reject.js'
const isOdd = n => n % 2 === 1
test('with array', () => {
expect(reject(isOdd)([ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])
})
test('with object', () => {
const obj = {
a : 1,
b : 2,
c : 3,
d : 4,
}
expect(reject(isOdd, obj)).toEqual({
b : 2,
d : 4,
})
})
```
TypeScript test
```typescript
import {reject} from 'rambda'
describe('R.reject with array', () => {
it('happy', () => {
const result = reject(
x => {
x // $ExpectType number
return x > 1
},
[1, 2, 3]
)
result // $ExpectType number[]
})
it('curried require explicit type', () => {
const result = reject(x => {
x // $ExpectType number
return x > 1
})([1, 2, 3])
result // $ExpectType number[]
})
})
describe('R.reject with objects', () => {
it('happy', () => {
const result = reject(
x => {
x // $ExpectType number
return x > 1
},
{a: 1, b: 2}
)
result // $ExpectType Dictionary
})
it('curried require dummy type', () => {
const result = reject(x => {
return x > 1
})({a: 1, b: 2})
result // $ExpectType Dictionary
})
})
```
[](#reject)
### removeIndex
```typescript
removeIndex(index: number, list: T[]): T[]
```
It returns a copy of `list` input with removed `index`.
Try this R.removeIndex example in Rambda REPL
All TypeScript definitions
```typescript
removeIndex(index: number, list: T[]): T[];
removeIndex(index: number): (list: T[]) => T[];
```
R.removeIndex source
```javascript
export function removeIndex(index, list){
if (arguments.length === 1) return _list => removeIndex(index, _list)
if (index <= 0) return list.slice(1)
if (index >= list.length - 1) return list.slice(0, list.length - 1)
return [ ...list.slice(0, index), ...list.slice(index + 1) ]
}
```
Tests
```javascript
import { removeIndex } from './removeIndex.js'
const list = [ 1, 2, 3, 4 ]
test('first or before first index', () => {
expect(removeIndex(-2, list)).toEqual([ 2, 3, 4 ])
expect(removeIndex(-2)(list)).toEqual([ 2, 3, 4 ])
})
test('last or after last index', () => {
expect(removeIndex(4, list)).toEqual([ 1, 2, 3 ])
expect(removeIndex(10, list)).toEqual([ 1, 2, 3 ])
})
test('middle index', () => {
expect(removeIndex(1, list)).toEqual([ 1, 3, 4 ])
expect(removeIndex(2, list)).toEqual([ 1, 2, 4 ])
})
```
TypeScript test
```typescript
import {removeIndex} from 'rambda'
describe('R.removeIndex', () => {
it('happy', () => {
const result = removeIndex(1, [1, 2, 3])
result // $ExpectType number[]
})
it('curried', () => {
const result = removeIndex(1)([1, 2, 3])
result // $ExpectType number[]
})
})
```
[](#removeIndex)
### repeat
```typescript
repeat(x: T): (timesToRepeat: number) => T[]
```
Try this R.repeat example in Rambda REPL
All TypeScript definitions
```typescript
repeat(x: T): (timesToRepeat: number) => T[];
repeat(x: T, timesToRepeat: number): T[];
```
R.repeat source
```javascript
export function repeat(x, timesToRepeat){
if (arguments.length === 1){
return _timesToRepeat => repeat(x, _timesToRepeat)
}
return Array(timesToRepeat).fill(x)
}
```
Tests
```javascript
import { repeat } from './repeat.js'
test('repeat', () => {
expect(repeat('')(3)).toEqual([ '', '', '' ])
expect(repeat('foo', 3)).toEqual([ 'foo', 'foo', 'foo' ])
const obj = {}
const arr = repeat(obj, 3)
expect(arr).toEqual([ {}, {}, {} ])
expect(arr[ 0 ] === arr[ 1 ]).toBeTrue()
})
```
TypeScript test
```typescript
import {repeat} from 'rambda'
describe('R.repeat', () => {
it('happy', () => {
const result = repeat(4, 7)
result // $ExpectType number[]
})
it('curried', () => {
const result = repeat(4)(7)
result // $ExpectType number[]
})
})
```
[](#repeat)
### replace
```typescript
replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string
```
It replaces `strOrRegex` found in `str` with `replacer`.
Try this R.replace example in Rambda REPL
All TypeScript definitions
```typescript
replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string;
replace(strOrRegex: RegExp | string, replacer: RegExpReplacer): (str: string) => string;
replace(strOrRegex: RegExp | string): (replacer: RegExpReplacer) => (str: string) => string;
```
R.replace source
```javascript
import { curry } from './curry.js'
function replaceFn(
pattern, replacer, str
){
return str.replace(pattern, replacer)
}
export const replace = curry(replaceFn)
```
Tests
```javascript
import { replace } from './replace.js'
test('happy', () => {
expect(replace(
/\s/g, '|', 'foo bar baz'
)).toBe('foo|bar|baz')
})
test('with function as replacer input', () => {
expect(replace(
/\s/g,
(
match, offset, str
) => {
expect(match).toBe(' ')
expect([ 3, 7 ].includes(offset)).toBeTrue()
expect(str).toBe('foo bar baz')
return '|'
},
'foo bar baz'
)).toBe('foo|bar|baz')
})
```
TypeScript test
```typescript
import {replace} from 'rambda'
const str = 'foo bar foo'
const replacer = 'bar'
describe('R.replace', () => {
it('happy', () => {
const result = replace(/foo/g, replacer, str)
result // $ExpectType string
})
it('with string as search pattern', () => {
const result = replace('foo', replacer, str)
result // $ExpectType string
})
it('with function as replacer', () => {
const result = replace('f(o)o', (m: string, p1: string, offset: number) => {
m // $ExpectType string
p1 // $ExpectType string
offset // $ExpectType number
return p1
}, str)
result // $ExpectType string
})
})
describe('R.replace - curried', () => {
it('happy', () => {
const result = replace(/foo/g, replacer)(str)
result // $ExpectType string
})
it('with string as search pattern', () => {
const result = replace('foo', replacer)(str)
result // $ExpectType string
})
it('with function as replacer', () => {
const result = replace('f(o)o')((m: string, p1: string, offset: number) => {
m // $ExpectType string
p1 // $ExpectType string
offset // $ExpectType number
return p1
})(str)
result // $ExpectType string
})
})
```
[](#replace)
### reverse
```typescript
reverse(input: T[]): T[]
```
It returns a reversed copy of list or string `input`.
Try this R.reverse example in Rambda REPL
All TypeScript definitions
```typescript
reverse(input: T[]): T[];
reverse(input: string): string;
```
R.reverse source
```javascript
export function reverse(listOrString) {
if (typeof listOrString === 'string') {
return listOrString.split('').reverse().join('')
}
const clone = listOrString.slice()
return clone.reverse()
}
```
Tests
```javascript
import {reverse} from './reverse.js'
test('happy', () => {
expect(reverse([1, 2, 3])).toEqual([3, 2, 1])
})
test('with string', () => {
expect(reverse('baz')).toBe('zab')
})
test("it doesn't mutate", () => {
const arr = [1, 2, 3]
expect(reverse(arr)).toEqual([3, 2, 1])
expect(arr).toEqual([1, 2, 3])
})
```
TypeScript test
```typescript
import {reverse} from 'rambda'
const list = [1, 2, 3, 4, 5]
describe('R.reverse', () => {
it('happy', () => {
const result = reverse(list)
result // $ExpectType number[]
})
})
```
[](#reverse)
### set
```typescript
set(lens: Lens): {
(a: A): (obj: S) => S
(a: A, obj: S): S
}
```
It returns a copied **Object** or **Array** with modified `lens` focus set to `replacer` value.
Try this R.set example in Rambda REPL
All TypeScript definitions
```typescript
set(lens: Lens): {
(a: A): (obj: S) => S
(a: A, obj: S): S
};
set(lens: Lens, a: A): (obj: S) => S;
set(lens: Lens, a: A, obj: S): S;
```
R.set source
```javascript
import {always} from './always.js'
import {curry} from './curry.js'
import {over} from './over.js'
function setFn(lens, replacer, x) {
return over(lens, always(replacer), x)
}
export const set = curry(setFn)
```
Tests
```javascript
import {assoc} from './assoc.js'
import {lens} from './lens.js'
import {lensIndex} from './lensIndex.js'
import {lensPath} from './lensPath.js'
import {prop} from './prop.js'
import {set} from './set.js'
const testObject = {
foo: 'bar',
baz: {
a: 'x',
b: 'y',
},
}
test('assoc lens', () => {
const assocLens = lens(prop('foo'), assoc('foo'))
const result = set(assocLens, 'FOO', testObject)
const expected = {
...testObject,
foo: 'FOO',
}
expect(result).toEqual(expected)
})
test('path lens', () => {
const pathLens = lensPath('baz.a')
const result = set(pathLens, 'z', testObject)
const expected = {
...testObject,
baz: {
a: 'z',
b: 'y',
},
}
expect(result).toEqual(expected)
})
test('index lens', () => {
const indexLens = lensIndex(0)
const result = set(indexLens, 3, [1, 2])
expect(result).toEqual([3, 2])
})
```
[](#set)
### slice
```typescript
slice(from: number, to: number, input: string): string
```
Try this R.slice example in Rambda REPL
All TypeScript definitions
```typescript
slice(from: number, to: number, input: string): string;
slice(from: number, to: number, input: T[]): T[];
slice(from: number, to: number): {
(input: string): string;
(input: T[]): T[];
};
slice(from: number): {
(to: number, input: string): string;
(to: number, input: T[]): T[];
};
```
R.slice source
```javascript
import { curry } from './curry.js'
function sliceFn(
from, to, list
){
return list.slice(from, to)
}
export const slice = curry(sliceFn)
```
Tests
```javascript
import { slice } from './slice.js'
test('slice', () => {
expect(slice(
1, 3, [ 'a', 'b', 'c', 'd' ]
)).toEqual([ 'b', 'c' ])
expect(slice(
1, Infinity, [ 'a', 'b', 'c', 'd' ]
)).toEqual([ 'b', 'c', 'd' ])
expect(slice(
0, -1, [ 'a', 'b', 'c', 'd' ]
)).toEqual([ 'a', 'b', 'c' ])
expect(slice(
-3, -1, [ 'a', 'b', 'c', 'd' ]
)).toEqual([ 'b', 'c' ])
expect(slice(
0, 3, 'ramda'
)).toBe('ram')
})
```
TypeScript test
```typescript
import {slice} from 'rambda'
const list = [1, 2, 3, 4, 5]
describe('R.slice', () => {
it('happy', () => {
const result = slice(1, 3, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = slice(1, 3)(list)
result // $ExpectType number[]
})
})
```
[](#slice)
### sort
```typescript
sort(sortFn: (a: T, b: T) => number, list: T[]): T[]
```
It returns copy of `list` sorted by `sortFn` function, where `sortFn` needs to return only `-1`, `0` or `1`.
Try this R.sort example in Rambda REPL
All TypeScript definitions
```typescript
sort(sortFn: (a: T, b: T) => number, list: T[]): T[];
sort(sortFn: (a: T, b: T) => number): (list: T[]) => T[];
```
R.sort source
```javascript
import { cloneList } from './_internals/cloneList.js'
export function sort(sortFn, list){
if (arguments.length === 1) return _list => sort(sortFn, _list)
return cloneList(list).sort(sortFn)
}
```
Tests
```javascript
import { sort } from './sort.js'
const fn = (a, b) => a > b ? 1 : -1
test('sort', () => {
expect(sort((a, b) => a - b)([ 2, 3, 1 ])).toEqual([ 1, 2, 3 ])
})
test('it doesn\'t mutate', () => {
const list = [ 'foo', 'bar', 'baz' ]
expect(sort(fn, list)).toEqual([ 'bar', 'baz', 'foo' ])
expect(list[ 0 ]).toBe('foo')
expect(list[ 1 ]).toBe('bar')
expect(list[ 2 ]).toBe('baz')
})
```
TypeScript test
```typescript
import {sort} from 'rambda'
const list = [3, 0, 5, 2, 1]
function sortFn(a: number, b: number): number {
return a > b ? 1 : -1
}
describe('R.sort', () => {
it('happy', () => {
const result = sort(sortFn, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = sort(sortFn)(list)
result // $ExpectType number[]
})
})
```
[](#sort)
### sortBy
```typescript
sortBy(sortFn: (a: T) => Ord, list: T[]): T[]
```
It returns copy of `list` sorted by `sortFn` function, where `sortFn` function returns a value to compare, i.e. it doesn't need to return only `-1`, `0` or `1`.
Try this R.sortBy example in Rambda REPL
All TypeScript definitions
```typescript
sortBy(sortFn: (a: T) => Ord, list: T[]): T[];
sortBy(sortFn: (a: T) => Ord): (list: T[]) => T[];
sortBy(sortFn: (a: any) => Ord): (list: T[]) => T[];
```
R.sortBy source
```javascript
import { cloneList } from './_internals/cloneList.js'
export function sortBy(sortFn, list){
if (arguments.length === 1) return _list => sortBy(sortFn, _list)
const clone = cloneList(list)
return clone.sort((a, b) => {
const aSortResult = sortFn(a)
const bSortResult = sortFn(b)
if (aSortResult === bSortResult) return 0
return aSortResult < bSortResult ? -1 : 1
})
}
```
Tests
```javascript
import { compose } from './compose.js'
import { prop } from './prop.js'
import { sortBy } from './sortBy.js'
import { toLower } from './toLower.js'
test('happy', () => {
const input = [ { a : 2 }, { a : 1 }, { a : 1 }, { a : 3 } ]
const expected = [ { a : 1 }, { a : 1 }, { a : 2 }, { a : 3 } ]
const result = sortBy(x => x.a)(input)
expect(result).toEqual(expected)
})
test('with compose', () => {
const alice = {
name : 'ALICE',
age : 101,
}
const bob = {
name : 'Bob',
age : -10,
}
const clara = {
name : 'clara',
age : 314.159,
}
const people = [ clara, bob, alice ]
const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name')))
expect(sortByNameCaseInsensitive(people)).toEqual([ alice, bob, clara ])
})
```
TypeScript test
```typescript
import {sortBy, pipe} from 'rambda'
interface Input {
a: number,
}
describe('R.sortBy', () => {
it('passing type to sort function', () => {
function fn(x: any): number {
return x.a
}
function fn2(x: Input): number {
return x.a
}
const input = [{a: 2}, {a: 1}, {a: 0}]
const result = sortBy(fn, input)
const curriedResult = sortBy(fn2)(input)
result // $ExpectType { a: number; }[]
curriedResult // $ExpectType Input[]
result[0].a // $ExpectType number
curriedResult[0].a // $ExpectType number
})
it('passing type to sort function and list', () => {
function fn(x: Input): number {
return x.a
}
const input: Input[] = [{a: 2}, {a: 1}, {a: 0}]
const result = sortBy(fn, input)
const curriedResult = sortBy(fn)(input)
result // $ExpectType Input[]
curriedResult // $ExpectType Input[]
result[0].a // $ExpectType number
})
it('with R.pipe', () => {
interface Obj {
value: number,
}
const fn = pipe(sortBy(x => x.value))
const result = fn([{value: 1}, {value: 2}])
result // $ExpectType Obj[]
})
})
```
[](#sortBy)
### sortWith
Try this R.sortWith example in Rambda REPL
[](#sortWith)
### split
```typescript
split(separator: string | RegExp): (str: string) => string[]
```
Curried version of `String.prototype.split`
Try this R.split example in Rambda REPL
All TypeScript definitions
```typescript
split(separator: string | RegExp): (str: string) => string[];
split(separator: string | RegExp, str: string): string[];
```
R.split source
```javascript
export function split(separator, str){
if (arguments.length === 1) return _str => split(separator, _str)
return str.split(separator)
}
```
Tests
```javascript
import { split } from './split.js'
const str = 'foo|bar|baz'
const splitChar = '|'
const expected = [ 'foo', 'bar', 'baz' ]
test('happy', () => {
expect(split(splitChar, str)).toEqual(expected)
})
test('curried', () => {
expect(split(splitChar)(str)).toEqual(expected)
})
```
TypeScript test
```typescript
import {split} from 'rambda'
const str = 'foo|bar|baz'
const splitChar = '|'
describe('R.split', () => {
it('happy', () => {
const result = split(splitChar, str)
result // $ExpectType string[]
})
it('curried', () => {
const result = split(splitChar)(str)
result // $ExpectType string[]
})
})
```
[](#split)
### splitAt
```typescript
splitAt(index: number, input: T[]): [T[], T[]]
```
It splits string or array at a given index.
Try this R.splitAt example in Rambda REPL
All TypeScript definitions
```typescript
splitAt(index: number, input: T[]): [T[], T[]];
splitAt(index: number, input: string): [string, string];
splitAt(index: number): {
(input: T[]): [T[], T[]];
(input: string): [string, string];
};
```
R.splitAt source
```javascript
import { isArray } from './_internals/isArray.js'
import { drop } from './drop.js'
import { maybe } from './maybe.js'
import { take } from './take.js'
export function splitAt(index, input){
if (arguments.length === 1){
return _list => splitAt(index, _list)
}
if (!input) throw new TypeError(`Cannot read property 'slice' of ${ input }`)
if (!isArray(input) && typeof input !== 'string') return [ [], [] ]
const correctIndex = maybe(
index < 0,
input.length + index < 0 ? 0 : input.length + index,
index
)
return [ take(correctIndex, input), drop(correctIndex, input) ]
}
```
Tests
```javascript
import { splitAt as splitAtRamda } from 'ramda'
import { splitAt } from './splitAt.js'
const list = [ 1, 2, 3 ]
const str = 'foo bar'
test('with array', () => {
const result = splitAt(2, list)
expect(result).toEqual([ [ 1, 2 ], [ 3 ] ])
})
test('with array - index is negative number', () => {
const result = splitAt(-6, list)
expect(result).toEqual([ [], list ])
})
test('with array - index is out of scope', () => {
const result = splitAt(4, list)
expect(result).toEqual([ [ 1, 2, 3 ], [] ])
})
test('with string', () => {
const result = splitAt(4, str)
expect(result).toEqual([ 'foo ', 'bar' ])
})
test('with string - index is negative number', () => {
const result = splitAt(-2, str)
expect(result).toEqual([ 'foo b', 'ar' ])
})
test('with string - index is out of scope', () => {
const result = splitAt(10, str)
expect(result).toEqual([ str, '' ])
})
test('with array - index is out of scope', () => {
const result = splitAt(4)(list)
expect(result).toEqual([ [ 1, 2, 3 ], [] ])
})
const badInputs = [ 1, true, /foo/g, {} ]
const throwingBadInputs = [ null, undefined ]
test('with bad inputs', () => {
throwingBadInputs.forEach(badInput => {
expect(() => splitAt(1, badInput)).toThrowWithMessage(TypeError,
`Cannot read property 'slice' of ${ badInput }`)
expect(() => splitAtRamda(1, badInput)).toThrowWithMessage(TypeError,
`Cannot read properties of ${ badInput } (reading 'slice')`)
})
badInputs.forEach(badInput => {
const result = splitAt(1, badInput)
const ramdaResult = splitAtRamda(1, badInput)
expect(result).toEqual(ramdaResult)
})
})
```
TypeScript test
```typescript
import {splitAt} from 'rambda'
const index = 1
const str = 'foo'
const list = [1, 2, 3]
describe('R.splitAt with array', () => {
it('happy', () => {
const result = splitAt(index, list)
result // $ExpectType [number[], number[]]
})
it('curried', () => {
const result = splitAt(index)(list)
result // $ExpectType [number[], number[]]
})
})
describe('R.splitAt with string', () => {
it('happy', () => {
const result = splitAt(index, str)
result // $ExpectType [string, string]
})
it('curried', () => {
const result = splitAt(index)(str)
result // $ExpectType [string, string]
})
})
```
[](#splitAt)
### splitEvery
```typescript
splitEvery(sliceLength: number, input: T[]): (T[])[]
```
It splits `input` into slices of `sliceLength`.
Try this R.splitEvery example in Rambda REPL
All TypeScript definitions
```typescript
splitEvery(sliceLength: number, input: T[]): (T[])[];
splitEvery(sliceLength: number, input: string): string[];
splitEvery(sliceLength: number): {
(input: string): string[];
(input: T[]): (T[])[];
};
```
R.splitEvery source
```javascript
export function splitEvery(sliceLength, listOrString){
if (arguments.length === 1){
return _listOrString => splitEvery(sliceLength, _listOrString)
}
if (sliceLength < 1){
throw new Error('First argument to splitEvery must be a positive integer')
}
const willReturn = []
let counter = 0
while (counter < listOrString.length){
willReturn.push(listOrString.slice(counter, counter += sliceLength))
}
return willReturn
}
```
Tests
```javascript
import { splitEvery } from './splitEvery.js'
test('happy', () => {
expect(splitEvery(3, [ 1, 2, 3, 4, 5, 6, 7 ])).toEqual([
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7 ],
])
expect(splitEvery(3)('foobarbaz')).toEqual([ 'foo', 'bar', 'baz' ])
})
test('with bad input', () => {
expect(() =>
expect(splitEvery(0)('foo')).toEqual([ 'f', 'o', 'o' ])).toThrowErrorMatchingInlineSnapshot('"First argument to splitEvery must be a positive integer"')
})
```
TypeScript test
```typescript
import {splitEvery} from 'rambda'
const list = [1, 2, 3, 4, 5, 6, 7]
describe('R.splitEvery', () => {
it('happy', () => {
const result = splitEvery(3, list)
result // $ExpectType number[][]
})
it('curried', () => {
const result = splitEvery(3)(list)
result // $ExpectType number[][]
})
})
```
[](#splitEvery)
### splitWhen
```typescript
splitWhen(predicate: Predicate, list: U[]): (U[])[]
```
It splits `list` to two arrays according to a `predicate` function.
The first array contains all members of `list` before `predicate` returns `true`.
Try this R.splitWhen example in Rambda REPL
All TypeScript definitions
```typescript
splitWhen(predicate: Predicate, list: U[]): (U[])[];
splitWhen(predicate: Predicate): (list: U[]) => (U[])[];
```
R.splitWhen source
```javascript
export function splitWhen(predicate, input){
if (arguments.length === 1){
return _input => splitWhen(predicate, _input)
}
if (!input)
throw new TypeError(`Cannot read property 'length' of ${ input }`)
const preFound = []
const postFound = []
let found = false
let counter = -1
while (counter++ < input.length - 1){
if (found){
postFound.push(input[ counter ])
} else if (predicate(input[ counter ])){
postFound.push(input[ counter ])
found = true
} else {
preFound.push(input[ counter ])
}
}
return [ preFound, postFound ]
}
```
Tests
```javascript
import { splitWhen as splitWhenRamda } from 'ramda'
import { equals } from './equals.js'
import { splitWhen } from './splitWhen.js'
const list = [ 1, 2, 1, 2 ]
test('happy', () => {
const result = splitWhen(equals(2), list)
expect(result).toEqual([ [ 1 ], [ 2, 1, 2 ] ])
})
test('when predicate returns false', () => {
const result = splitWhen(equals(3))(list)
expect(result).toEqual([ list, [] ])
})
const badInputs = [ 1, true, /foo/g, {} ]
const throwingBadInputs = [ null, undefined ]
test('with bad inputs', () => {
throwingBadInputs.forEach(badInput => {
expect(() => splitWhen(equals(2), badInput)).toThrowWithMessage(TypeError,
`Cannot read property 'length' of ${ badInput }`)
expect(() => splitWhenRamda(equals(2), badInput)).toThrowWithMessage(TypeError,
`Cannot read properties of ${ badInput } (reading 'length')`)
})
badInputs.forEach(badInput => {
const result = splitWhen(equals(2), badInput)
const ramdaResult = splitWhenRamda(equals(2), badInput)
expect(result).toEqual(ramdaResult)
})
})
```
TypeScript test
```typescript
import {splitWhen} from 'rambda'
const list = [1, 2, 1, 2]
const predicate = (x: number) => x === 2
describe('R.splitWhen', () => {
it('happy', () => {
const result = splitWhen(predicate, list)
result // $ExpectType number[][]
})
it('curried', () => {
const result = splitWhen(predicate)(list)
result // $ExpectType number[][]
})
})
```
[](#splitWhen)
### startsWith
```typescript
startsWith(question: T, input: string): boolean
```
When iterable is a string, then it behaves as `String.prototype.startsWith`.
When iterable is a list, then it uses R.equals to determine if the target list starts in the same way as the given target.
Try this R.startsWith example in Rambda REPL
All TypeScript definitions
```typescript
startsWith(question: T, input: string): boolean;
startsWith(question: T): (input: string) => boolean;
startsWith(question: T[], input: T[]): boolean;
startsWith(question: T[]): (input: T[]) => boolean;
```
R.startsWith source
```javascript
import { isArray } from './_internals/isArray.js'
import { equals } from './equals.js'
export function startsWith(question, iterable){
if (arguments.length === 1)
return _iterable => startsWith(question, _iterable)
if (typeof iterable === 'string'){
return iterable.startsWith(question)
}
if (!isArray(question)) return false
let correct = true
const filtered = question.filter((x, index) => {
if (!correct) return false
const result = equals(x, iterable[ index ])
if (!result) correct = false
return result
})
return filtered.length === question.length
}
```
Tests
```javascript
import { startsWith as startsWithRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'
import { possibleIterables, possibleTargets } from './endsWith.spec.js'
import { startsWith } from './startsWith.js'
test('with string', () => {
expect(startsWith('foo', 'foo-bar')).toBeTrue()
expect(startsWith('baz')('foo-bar')).toBeFalse()
})
test('use R.equals with array', () => {
const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
expect(startsWith({ a : 1 }, list)).toBeFalse()
expect(startsWith([ { a : 1 } ], list)).toBeTrue()
expect(startsWith([ { a : 1 }, { a : 2 } ], list)).toBeTrue()
expect(startsWith(list, list)).toBeTrue()
expect(startsWith([ { a : 2 } ], list)).toBeFalse()
})
describe('brute force', () => {
compareCombinations({
fn : startsWith,
fnRamda : startsWithRamda,
firstInput : possibleTargets,
secondInput : possibleIterables,
callback : errorsCounters => {
expect(errorsCounters).toMatchInlineSnapshot(`
{
"ERRORS_MESSAGE_MISMATCH": 0,
"ERRORS_TYPE_MISMATCH": 0,
"RESULTS_MISMATCH": 0,
"SHOULD_NOT_THROW": 0,
"SHOULD_THROW": 0,
"TOTAL_TESTS": 32,
}
`)
},
})
})
```
TypeScript test
```typescript
import {startsWith} from 'rambda'
describe('R.startsWith - array', () => {
const question = [{a: 1}]
const iterable = [{a: 1}, {a: 2}]
it('happy', () => {
const result = startsWith(question, iterable)
result // $ExpectType boolean
})
it('curried', () => {
const result = startsWith(question)(iterable)
result // $ExpectType boolean
})
})
describe('R.startsWith - string', () => {
const question = 'foo'
const iterable = 'foo bar'
it('happy', () => {
const result = startsWith(question, iterable)
result // $ExpectType boolean
})
it('curried', () => {
const result = startsWith(question)(iterable)
result // $ExpectType boolean
})
})
```
[](#startsWith)
### subtract
Curried version of `x - y`
Try this R.subtract example in Rambda REPL
[](#subtract)
### sum
```typescript
sum(list: number[]): number
```
Try this R.sum example in Rambda REPL
All TypeScript definitions
```typescript
sum(list: number[]): number;
```
R.sum source
```javascript
export function sum(list){
return list.reduce((prev, current) => prev + current, 0)
}
```
Tests
```javascript
import { sum } from './sum.js'
test('happy', () => {
expect(sum([ 1, 2, 3, 4, 5 ])).toBe(15)
})
```
[](#sum)
### symmetricDifference
```typescript
symmetricDifference(x: T[], y: T[]): T[]
```
It returns a merged list of `x` and `y` with all equal elements removed.
`R.equals` is used to determine equality.
Try this R.symmetricDifference example in Rambda REPL
All TypeScript definitions
```typescript
symmetricDifference(x: T[], y: T[]): T[];
symmetricDifference(x: T[]): (y: T[]) => T[];
```
R.symmetricDifference source
```javascript
import { concat } from './concat.js'
import { filter } from './filter.js'
import { includes } from './includes.js'
export function symmetricDifference(x, y){
if (arguments.length === 1){
return _y => symmetricDifference(x, _y)
}
return concat(filter(value => !includes(value, y), x),
filter(value => !includes(value, x), y))
}
```
Tests
```javascript
import { symmetricDifference } from './symmetricDifference.js'
test('symmetricDifference', () => {
const list1 = [ 1, 2, 3, 4 ]
const list2 = [ 3, 4, 5, 6 ]
expect(symmetricDifference(list1)(list2)).toEqual([ 1, 2, 5, 6 ])
expect(symmetricDifference([], [])).toEqual([])
})
test('symmetricDifference with objects', () => {
const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]
expect(symmetricDifference(list1)(list2)).toEqual([
{ id : 1 },
{ id : 2 },
{ id : 5 },
{ id : 6 },
])
})
```
TypeScript test
```typescript
import {symmetricDifference} from 'rambda'
describe('R.symmetricDifference', () => {
it('happy', () => {
const list1 = [1, 2, 3, 4]
const list2 = [3, 4, 5, 6]
const result = symmetricDifference(list1, list2)
result // $ExpectType number[]
})
it('curried', () => {
const list1 = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]
const list2 = [{id: 3}, {id: 4}, {id: 5}, {id: 6}]
const result = symmetricDifference(list1)(list2)
result // $ExpectType { id: number; }[]
})
})
```
[](#symmetricDifference)
### T
```typescript
T(): boolean
```
Try this R.T example in Rambda REPL
All TypeScript definitions
```typescript
T(): boolean;
```
R.T source
```javascript
export function T(){
return true
}
```
[](#T)
### tail
```typescript
tail(input: T): T extends [any, ...infer U] ? U : [...T]
```
It returns all but the first element of `input`.
Try this R.tail example in Rambda REPL
All TypeScript definitions
```typescript
tail(input: T): T extends [any, ...infer U] ? U : [...T];
tail(input: string): string;
```
R.tail source
```javascript
import { drop } from './drop.js'
export function tail(listOrString){
return drop(1, listOrString)
}
```
Tests
```javascript
import { tail } from './tail.js'
test('tail', () => {
expect(tail([ 1, 2, 3 ])).toEqual([ 2, 3 ])
expect(tail([ 1, 2 ])).toEqual([ 2 ])
expect(tail([ 1 ])).toEqual([])
expect(tail([])).toEqual([])
expect(tail('abc')).toBe('bc')
expect(tail('ab')).toBe('b')
expect(tail('a')).toBe('')
expect(tail('')).toBe('')
})
```
TypeScript test
```typescript
import {tail} from 'rambda'
describe('R.tail', () => {
it('with string', () => {
const result = tail('foo')
result // $ExpectType string
})
it('with list - one type', () => {
const result = tail([1, 2, 3])
result // $ExpectType number[]
})
it('with list - mixed types', () => {
const result = tail(['foo', 'bar', 1, 2, 3])
result // $ExpectType (string | number)[]
})
})
```
[](#tail)
### take
```typescript
take(howMany: number, input: T[]): T[]
```
It returns the first `howMany` elements of `input`.
Try this R.take example in Rambda REPL
All TypeScript definitions
```typescript
take(howMany: number, input: T[]): T[];
take(howMany: number, input: string): string;
take(howMany: number): {
(input: T[]): T[];
(input: string): string;
};
```
R.take source
```javascript
import baseSlice from './_internals/baseSlice.js'
export function take(howMany, listOrString){
if (arguments.length === 1)
return _listOrString => take(howMany, _listOrString)
if (howMany < 0) return listOrString.slice()
if (typeof listOrString === 'string') return listOrString.slice(0, howMany)
return baseSlice(
listOrString, 0, howMany
)
}
```
Tests
```javascript
import { take } from './take.js'
test('happy', () => {
const arr = [ 'foo', 'bar', 'baz' ]
expect(take(1, arr)).toEqual([ 'foo' ])
expect(arr).toEqual([ 'foo', 'bar', 'baz' ])
expect(take(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar' ])
expect(take(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
expect(take(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
expect(take(3)('rambda')).toBe('ram')
})
test('with negative index', () => {
expect(take(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
expect(take(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})
test('with zero index', () => {
expect(take(0, [ 1, 2, 3 ])).toEqual([])
})
```
TypeScript test
```typescript
import {take} from 'rambda'
const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2
describe('R.take - array', () => {
it('happy', () => {
const result = take(howMany, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = take(howMany)(list)
result // $ExpectType number[]
})
})
describe('R.take - string', () => {
it('happy', () => {
const result = take(howMany, str)
result // $ExpectType string
})
it('curried', () => {
const result = take(howMany)(str)
result // $ExpectType string
})
})
```
[](#take)
### takeLast
```typescript
takeLast(howMany: number, input: T[]): T[]
```
It returns the last `howMany` elements of `input`.
Try this R.takeLast example in Rambda REPL
All TypeScript definitions
```typescript
takeLast(howMany: number, input: T[]): T[];
takeLast(howMany: number, input: string): string;
takeLast(howMany: number): {
(input: T[]): T[];
(input: string): string;
};
```
R.takeLast source
```javascript
import baseSlice from './_internals/baseSlice.js'
export function takeLast(howMany, listOrString){
if (arguments.length === 1)
return _listOrString => takeLast(howMany, _listOrString)
const len = listOrString.length
if (howMany < 0) return listOrString.slice()
let numValue = howMany > len ? len : howMany
if (typeof listOrString === 'string')
return listOrString.slice(len - numValue)
numValue = len - numValue
return baseSlice(
listOrString, numValue, len
)
}
```
Tests
```javascript
import { takeLast } from './takeLast.js'
test('with arrays', () => {
expect(takeLast(1, [ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ])
expect(takeLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'bar', 'baz' ])
expect(takeLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
expect(takeLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
expect(takeLast(10, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])
})
test('with strings', () => {
expect(takeLast(3, 'rambda')).toBe('bda')
expect(takeLast(7, 'rambda')).toBe('rambda')
})
test('with negative index', () => {
expect(takeLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
expect(takeLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])
})
```
TypeScript test
```typescript
import {takeLast} from 'rambda'
const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2
describe('R.takeLast - array', () => {
it('happy', () => {
const result = takeLast(howMany, list)
result // $ExpectType number[]
})
it('curried', () => {
const result = takeLast(howMany)(list)
result // $ExpectType number[]
})
})
describe('R.takeLast - string', () => {
it('happy', () => {
const result = takeLast(howMany, str)
result // $ExpectType string
})
it('curried', () => {
const result = takeLast(howMany)(str)
result // $ExpectType string
})
})
```
[](#takeLast)
### takeLastWhile
```typescript
takeLastWhile(predicate: (x: string) => boolean, input: string): string
```
Try this R.takeLastWhile example in Rambda REPL
All TypeScript definitions
```typescript
takeLastWhile(predicate: (x: string) => boolean, input: string): string;
takeLastWhile(predicate: (x: string) => boolean): (input: string) => string;
takeLastWhile(predicate: (x: T) => boolean, input: T[]): T[];
takeLastWhile(predicate: (x: T) => boolean): (input: T[]) => T[];
```
R.takeLastWhile source
```javascript
import { isArray } from './_internals/isArray.js'
export function takeLastWhile(predicate, input){
if (arguments.length === 1){
return _input => takeLastWhile(predicate, _input)
}
if (input.length === 0) return input
const toReturn = []
let counter = input.length
while (counter){
const item = input[ --counter ]
if (!predicate(item)){
break
}
toReturn.push(item)
}
return isArray(input) ? toReturn.reverse() : toReturn.reverse().join('')
}
```
Tests
```javascript
import { takeLastWhile } from './takeLastWhile.js'
const assert = require('assert')
const list = [ 1, 2, 3, 4 ]
test('happy', () => {
const predicate = x => x > 2
const result = takeLastWhile(predicate, list)
expect(result).toEqual([ 3, 4 ])
})
test('predicate is always true', () => {
const predicate = () => true
const result = takeLastWhile(predicate)(list)
expect(result).toEqual(list)
})
test('predicate is always false', () => {
const predicate = () => false
const result = takeLastWhile(predicate, list)
expect(result).toEqual([])
})
test('with string', () => {
const result = takeLastWhile(x => x !== 'F', 'FOOBAR')
expect(result).toBe('OOBAR')
})
```
TypeScript test
```typescript
import {takeLastWhile} from 'rambda'
const list = [1, 2, 3]
const str = 'FOO'
describe('R.takeLastWhile', () => {
it('with array', () => {
const result = takeLastWhile(x => x > 1, list)
result // $ExpectType number[]
})
it('with array - curried', () => {
const result = takeLastWhile(x => x > 1, list)
result // $ExpectType number[]
})
it('with string', () => {
const result = takeLastWhile(x => x !== 'F', str)
result // $ExpectType string
})
it('with string - curried', () => {
const result = takeLastWhile(x => x !== 'F')(str)
result // $ExpectType string
})
})
```
[](#takeLastWhile)
### takeWhile
Try this R.takeWhile example in Rambda REPL
[](#takeWhile)
### tap
```typescript
tap(fn: (x: T) => void, input: T): T
```
It applies function `fn` to input `x` and returns `x`.
One use case is debugging in the middle of `R.compose`.
Try this R.tap example in Rambda REPL
All TypeScript definitions
```typescript
tap(fn: (x: T) => void, input: T): T;
tap(fn: (x: T) => void): (input: T) => T;
```
R.tap source
```javascript
export function tap(fn, x){
if (arguments.length === 1) return _x => tap(fn, _x)
fn(x)
return x
}
```
Tests
```javascript
import { tap } from './tap.js'
test('tap', () => {
let a = 1
const sayX = x => a = x
expect(tap(sayX, 100)).toBe(100)
expect(tap(sayX)(100)).toBe(100)
expect(a).toBe(100)
})
```
TypeScript test
```typescript
import {tap, pipe} from 'rambda'
describe('R.tap', () => {
it('happy', () => {
pipe(
tap(x => {
x // $ExpectType number[]
}),
(x: number[]) => x.length
)([1, 2])
})
})
```
[](#tap)
### test
```typescript
test(regExpression: RegExp): (str: string) => boolean
```
It determines whether `str` matches `regExpression`.
Try this R.test example in Rambda REPL
All TypeScript definitions
```typescript
test(regExpression: RegExp): (str: string) => boolean;
test(regExpression: RegExp, str: string): boolean;
```
R.test source
```javascript
export function test(pattern, str){
if (arguments.length === 1) return _str => test(pattern, _str)
if (typeof pattern === 'string'){
throw new TypeError(`R.test requires a value of type RegExp as its first argument; received "${ pattern }"`)
}
return str.search(pattern) !== -1
}
```
Tests
```javascript
import { test as testMethod } from './test.js'
test('happy', () => {
expect(testMethod(/^x/, 'xyz')).toBeTrue()
expect(testMethod(/^y/)('xyz')).toBeFalse()
})
test('throws if first argument is not regex', () => {
expect(() => testMethod('foo', 'bar')).toThrowErrorMatchingInlineSnapshot('"R.test requires a value of type RegExp as its first argument; received "foo""')
})
```
TypeScript test
```typescript
import {test} from 'rambda'
const input = 'foo '
const regex = /foo/
describe('R.test', () => {
it('happy', () => {
const result = test(regex, input)
result // $ExpectType boolean
})
it('curried', () => {
const result = test(regex)(input)
result // $ExpectType boolean
})
})
```
[](#test)
### times
```typescript
times(fn: (i: number) => T, howMany: number): T[]
```
It returns the result of applying function `fn` over members of range array.
The range array includes numbers between `0` and `howMany`(exclusive).
Try this R.times example in Rambda REPL
All TypeScript definitions
```typescript
times(fn: (i: number) => T, howMany: number): T[];
times(fn: (i: number) => T): (howMany: number) => T[];
```
R.times source
```javascript
import { isInteger } from './_internals/isInteger.js'
import { map } from './map.js'
import { range } from './range.js'
export function times(fn, howMany){
if (arguments.length === 1) return _howMany => times(fn, _howMany)
if (!isInteger(howMany) || howMany < 0){
throw new RangeError('n must be an integer')
}
return map(fn, range(0, howMany))
}
```
Tests
```javascript
import assert from 'assert'
import { identity } from './identity.js'
import { times } from './times.js'
test('happy', () => {
const result = times(identity, 5)
expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})
test('with bad input', () => {
assert.throws(() => {
times(3)('cheers!')
}, RangeError)
assert.throws(() => {
times(identity, -1)
}, RangeError)
})
test('curry', () => {
const result = times(identity)(5)
expect(result).toEqual([ 0, 1, 2, 3, 4 ])
})
```
TypeScript test
```typescript
import {times, identity} from 'rambda'
describe('R.times', () => {
it('happy', () => {
const result = times(identity, 5)
result // $ExpectType number[]
})
})
```
[](#times)
### toLower
```typescript
toLower(str: S): Lowercase
```
Try this R.toLower example in Rambda REPL
All TypeScript definitions
```typescript
toLower(str: S): Lowercase;
toLower(str: string): string;
```
R.toLower source
```javascript
export function toLower(str){
return str.toLowerCase()
}
```
Tests
```javascript
import { toLower } from './toLower.js'
test('toLower', () => {
expect(toLower('FOO|BAR|BAZ')).toBe('foo|bar|baz')
})
```
[](#toLower)
### toPairs
```typescript
toPairs>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>
```
It transforms an object to a list.
Try this R.toPairs example in Rambda REPL
All TypeScript definitions
```typescript
toPairs>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>;
toPairs(obj: Record): Array<[string, S]>;
```
R.toPairs source
```javascript
export function toPairs(obj){
return Object.entries(obj)
}
```
Tests
```javascript
import { toPairs } from './toPairs.js'
const obj = {
a : 1,
b : 2,
c : [ 3, 4 ],
}
const expected = [
[ 'a', 1 ],
[ 'b', 2 ],
[ 'c', [ 3, 4 ] ],
]
test('happy', () => {
expect(toPairs(obj)).toEqual(expected)
})
```
[](#toPairs)
### toString
```typescript
toString(x: unknown): string
```
Try this R.toString example in Rambda REPL
All TypeScript definitions
```typescript
toString(x: unknown): string;
```
R.toString source
```javascript
export function toString(x){
return x.toString()
}
```
Tests
```javascript
import { toString } from './toString.js'
test('happy', () => {
expect(toString([ 1, 2, 3 ])).toBe('1,2,3')
})
```
[](#toString)
### toUpper
```typescript
toUpper(str: S): Uppercase
```
Try this R.toUpper example in Rambda REPL
All TypeScript definitions
```typescript
toUpper(str: S): Uppercase;
toUpper(str: string): string;
```
R.toUpper source
```javascript
export function toUpper(str){
return str.toUpperCase()
}
```
Tests
```javascript
import { toUpper } from './toUpper.js'
test('toUpper', () => {
expect(toUpper('foo|bar|baz')).toBe('FOO|BAR|BAZ')
})
```
[](#toUpper)
### transpose
```typescript
transpose(list: (T[])[]): (T[])[]
```
Try this R.transpose example in Rambda REPL
All TypeScript definitions
```typescript
transpose(list: (T[])[]): (T[])[];
```
R.transpose source
```javascript
import { isArray } from './_internals/isArray.js'
export function transpose(array){
return array.reduce((acc, el) => {
el.forEach((nestedEl, i) =>
isArray(acc[ i ]) ? acc[ i ].push(nestedEl) : acc.push([ nestedEl ]))
return acc
}, [])
}
```
Tests
```javascript
import { transpose } from './transpose.js'
test('happy', () => {
const input = [
[ 'a', 1 ],
[ 'b', 2 ],
[ 'c', 3 ],
]
expect(transpose(input)).toEqual([
[ 'a', 'b', 'c' ],
[ 1, 2, 3 ],
])
})
test('when rows are shorter', () => {
const actual = transpose([ [ 10, 11 ], [ 20 ], [], [ 30, 31, 32 ] ])
const expected = [ [ 10, 20, 30 ], [ 11, 31 ], [ 32 ] ]
expect(actual).toEqual(expected)
})
test('with empty array', () => {
expect(transpose([])).toEqual([])
})
test('array with falsy values', () => {
const actual = transpose([
[ true, false, undefined, null ],
[ null, undefined, false, true ],
])
const expected = [
[ true, null ],
[ false, undefined ],
[ undefined, false ],
[ null, true ],
]
expect(actual).toEqual(expected)
})
```
TypeScript test
```typescript
import {transpose} from 'rambda'
const input = [
['a', 1],
['b', 2],
['c', 3],
]
describe('R.transpose', () => {
it('happy', () => {
const result = transpose(input)
result // $ExpectType (string | number)[][]
})
})
```
[](#transpose)
### trim
```typescript
trim(str: string): string
```
Try this R.trim example in Rambda REPL
All TypeScript definitions
```typescript
trim(str: string): string;
```
R.trim source
```javascript
export function trim(str){
return str.trim()
}
```
Tests
```javascript
import { trim } from './trim.js'
test('trim', () => {
expect(trim(' foo ')).toBe('foo')
})
```
[](#trim)
### tryCatch
It returns function that runs `fn` in `try/catch` block. If there was an error, then `fallback` is used to return the result. Note that `fn` can be value or asynchronous/synchronous function(unlike `Ramda` where fallback can only be a synchronous function).
Try this R.tryCatch example in Rambda REPL
[](#tryCatch)
### type
It accepts any input and it returns its type.
Try this R.type example in Rambda REPL
[](#type)
### unapply
```typescript
unapply(fn: (args: any[]) => T): (...args: any[]) => T
```
It calls a function `fn` with the list of values of the returned function.
`R.unapply` is the opposite of `R.apply` method.
Try this R.unapply example in Rambda REPL
All TypeScript definitions
```typescript
unapply(fn: (args: any[]) => T): (...args: any[]) => T;
```
R.unapply source
```javascript
export function unapply(fn){
return function (...args){
return fn.call(this, args)
}
}
```
Tests
```javascript
import { apply } from './apply.js'
import { converge } from './converge.js'
import { identity } from './identity.js'
import { prop } from './prop.js'
import { sum } from './sum.js'
import { unapply } from './unapply.js'
test('happy', () => {
const fn = unapply(identity)
expect(fn(
1, 2, 3
)).toEqual([ 1, 2, 3 ])
expect(fn()).toEqual([])
})
test('returns a function which is always passed one argument', () => {
const fn = unapply(function (){
return arguments.length
})
expect(fn('x')).toBe(1)
expect(fn('x', 'y')).toBe(1)
expect(fn(
'x', 'y', 'z'
)).toBe(1)
})
test('forwards arguments to decorated function as an array', () => {
const fn = unapply(xs => '[' + xs + ']')
expect(fn(2)).toBe('[2]')
expect(fn(2, 4)).toBe('[2,4]')
expect(fn(
2, 4, 6
)).toBe('[2,4,6]')
})
test('returns a function with length 0', () => {
const fn = unapply(identity)
expect(fn).toHaveLength(0)
})
test('is the inverse of R.apply', () => {
let a, b, c, d, e, f, g, n
const rand = function (){
return Math.floor(200 * Math.random()) - 100
}
f = Math.max
g = unapply(apply(f))
n = 1
while (n <= 100){
a = rand()
b = rand()
c = rand()
d = rand()
e = rand()
expect(f(
a, b, c, d, e
)).toEqual(g(
a, b, c, d, e
))
n += 1
}
f = function (xs){
return '[' + xs + ']'
}
g = apply(unapply(f))
n = 1
while (n <= 100){
a = rand()
b = rand()
c = rand()
d = rand()
e = rand()
expect(f([ a, b, c, d, e ])).toEqual(g([ a, b, c, d, e ]))
n += 1
}
})
test('it works with converge', () => {
const fn = unapply(sum)
const convergeFn = converge(fn, [ prop('a'), prop('b'), prop('c') ])
const obj = {
a : 1337,
b : 42,
c : 1,
}
const expected = 1337 + 42 + 1
expect(convergeFn(obj)).toEqual(expected)
})
```
TypeScript test
```typescript
import {join, unapply, sum} from 'rambda'
describe('R.unapply', () => {
it('happy', () => {
const fn = unapply(sum)
fn(1, 2, 3) // $ExpectType number
})
it('joins a string', () => {
const fn = unapply(join(''))
fn('s', 't', 'r', 'i', 'n', 'g') // $ExpectType string
})
})
```
[](#unapply)
### union
```typescript
union(x: T[], y: T[]): T[]
```
It takes two lists and return a new list containing a merger of both list with removed duplicates.
`R.equals` is used to compare for duplication.
Try this R.union example in Rambda REPL
All TypeScript definitions
```typescript
union(x: T[], y: T[]): T[];
union(x: T[]): (y: T[]) => T[];
```
R.union source
```javascript
import { cloneList } from './_internals/cloneList.js'
import { includes } from './includes.js'
export function union(x, y){
if (arguments.length === 1) return _y => union(x, _y)
const toReturn = cloneList(x)
y.forEach(yInstance => {
if (!includes(yInstance, x)) toReturn.push(yInstance)
})
return toReturn
}
```
Tests
```javascript
import { union } from './union.js'
test('happy', () => {
expect(union([ 1, 2 ], [ 2, 3 ])).toEqual([ 1, 2, 3 ])
})
test('with list of objects', () => {
const list1 = [ { a : 1 }, { a : 2 } ]
const list2 = [ { a : 2 }, { a : 3 } ]
const result = union(list1)(list2)
})
```
TypeScript test
```typescript
import {union} from 'rambda'
describe('R.union', () => {
it('happy', () => {
const result = union([1, 2], [2, 3])
result // $ExpectType number[]
})
it('with array of objects - case 1', () => {
const list1 = [{a: 1}, {a: 2}]
const list2 = [{a: 2}, {a: 3}]
const result = union(list1, list2)
result // $ExpectType { a: number; }[]
})
it('with array of objects - case 2', () => {
const list1 = [{a: 1, b: 1}, {a: 2}]
const list2 = [{a: 2}, {a: 3, b: 3}]
const result = union(list1, list2)
result[0].a // $ExpectType number
result[0].b // $ExpectType number | undefined
})
})
describe('R.union - curried', () => {
it('happy', () => {
const result = union([1, 2])([2, 3])
result // $ExpectType number[]
})
it('with array of objects - case 1', () => {
const list1 = [{a: 1}, {a: 2}]
const list2 = [{a: 2}, {a: 3}]
const result = union(list1)(list2)
result // $ExpectType { a: number; }[]
})
it('with array of objects - case 2', () => {
const list1 = [{a: 1, b: 1}, {a: 2}]
const list2 = [{a: 2}, {a: 3, b: 3}]
const result = union(list1)(list2)
result[0].a // $ExpectType number
result[0].b // $ExpectType number | undefined
})
})
```
[](#union)
### uniq
```typescript
uniq(list: T[]): T[]
```
It returns a new array containing only one copy of each element of `list`.
`R.equals` is used to determine equality.
Try this R.uniq example in Rambda REPL
All TypeScript definitions
```typescript
uniq(list: T[]): T[];
```
R.uniq source
```javascript
import { _Set } from './_internals/set.js'
export function uniq(list){
const set = new _Set()
const willReturn = []
list.forEach(item => {
if (set.checkUniqueness(item)){
willReturn.push(item)
}
})
return willReturn
}
```
Tests
```javascript
import { uniq } from './uniq.js'
test('happy', () => {
const list = [ 1, 2, 3, 3, 3, 1, 2, 0 ]
expect(uniq(list)).toEqual([ 1, 2, 3, 0 ])
})
test('with object', () => {
const list = [ { a : 1 }, { a : 2 }, { a : 1 }, { a : 2 } ]
expect(uniq(list)).toEqual([ { a : 1 }, { a : 2 } ])
})
test('with nested array', () => {
expect(uniq([ [ 42 ], [ 42 ] ])).toEqual([ [ 42 ] ])
})
test('with booleans', () => {
expect(uniq([ [ false ], [ false ], [ true ] ])).toEqual([ [ false ], [ true ] ])
})
test('with falsy values', () => {
expect(uniq([ undefined, null ])).toEqual([ undefined, null ])
})
test('can distinct between string and number', () => {
expect(uniq([ 1, '1' ])).toEqual([ 1, '1' ])
})
```
TypeScript test
```typescript
import {uniq} from 'rambda'
describe('R.uniq', () => {
it('happy', () => {
const result = uniq([1, 2, 3, 3, 3, 1, 2, 0])
result // $ExpectType number[]
})
})
```
[](#uniq)
### uniqBy
It applies uniqueness to input list based on function that defines what to be used for comparison between elements.
`R.equals` is used to determine equality.
Try this R.uniqBy example in Rambda REPL
[](#uniqBy)
### uniqWith
```typescript
uniqWith(predicate: (x: T, y: T) => boolean, list: T[]): T[]
```
It returns a new array containing only one copy of each element in `list` according to `predicate` function.
This predicate should return true, if two elements are equal.
Try this R.uniqWith example in Rambda REPL
All TypeScript definitions
```typescript
uniqWith(predicate: (x: T, y: T) => boolean, list: T[]): T[];
uniqWith(predicate: (x: T, y: T) => boolean): (list: T[]) => T[];
```
R.uniqWith source
```javascript
function includesWith(
predicate, target, list
){
let willReturn = false
let index = -1
while (++index < list.length && !willReturn){
const value = list[ index ]
if (predicate(target, value)){
willReturn = true
}
}
return willReturn
}
export function uniqWith(predicate, list){
if (arguments.length === 1) return _list => uniqWith(predicate, _list)
let index = -1
const willReturn = []
while (++index < list.length){
const value = list[ index ]
if (!includesWith(
predicate, value, willReturn
)){
willReturn.push(value)
}
}
return willReturn
}
```
Tests
```javascript
import { uniqWith as uniqWithRamda } from 'ramda'
import { uniqWith } from './uniqWith.js'
const list = [ { a : 1 }, { a : 1 } ]
test('happy', () => {
const fn = (x, y) => x.a === y.a
const result = uniqWith(fn, list)
expect(result).toEqual([ { a : 1 } ])
})
test('with list of strings', () => {
const fn = (x, y) => x.length === y.length
const list = [ '0', '11', '222', '33', '4', '55' ]
const result = uniqWith(fn)(list)
const resultRamda = uniqWithRamda(fn, list)
expect(result).toEqual([ '0', '11', '222' ])
expect(resultRamda).toEqual([ '0', '11', '222' ])
})
```
TypeScript test
```typescript
import {uniqWith} from 'rambda'
describe('R.uniqWith', () => {
it('happy', () => {
const list = [{a: 1}, {a: 1}]
const fn = (x: any, y: any) => x.a === y.a
const result = uniqWith(fn, list)
result // $ExpectType { a: number; }[]
})
})
```
[](#uniqWith)
### unless
```typescript
unless(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U
```
The method returns function that will be called with argument `input`.
If `predicate(input)` returns `false`, then the end result will be the outcome of `whenFalse(input)`.
In the other case, the final output will be the `input` itself.
Try this R.unless example in Rambda REPL
All TypeScript definitions
```typescript
unless(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U;
unless(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U): (x: T) => T | U;
unless(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T, x: T): T;
unless(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T): (x: T) => T;
```
R.unless source
```javascript
export function unless(predicate, whenFalse){
if (arguments.length === 1){
return _whenFalse => unless(predicate, _whenFalse)
}
return input => predicate(input) ? input : whenFalse(input)
}
```
Tests
```javascript
import { inc } from './inc.js'
import { isNil } from './isNil.js'
import { unless } from './unless.js'
test('happy', () => {
const safeInc = unless(isNil, inc)
expect(safeInc(null)).toBeNull()
expect(safeInc(1)).toBe(2)
})
test('curried', () => {
const safeIncCurried = unless(isNil)(inc)
expect(safeIncCurried(null)).toBeNull()
})
```
TypeScript test
```typescript
import {unless, inc} from 'rambda'
describe('R.unless', () => {
it('happy', () => {
const fn = unless(x => x > 5, inc)
const result = fn(1)
result // $ExpectType number
})
it('with one explicit type', () => {
const result = unless(
x => {
x // $ExpectType number
return x > 5
},
x => {
x // $ExpectType number
return x + 1
},
1
)
result // $ExpectType number
})
it('with two different explicit types', () => {
const result = unless(
x => {
x // $ExpectType number
return x > 5
},
x => {
x // $ExpectType number
return `${x}-foo`
},
1
)
result // $ExpectType string | number
})
})
describe('R.unless - curried', () => {
it('happy', () => {
const fn = unless(x => x > 5, inc)
const result = fn(1)
result // $ExpectType number
})
it('with one explicit type', () => {
const fn = unless(
x => {
x // $ExpectType number
return x > 5
},
x => {
x // $ExpectType number
return x + 1
}
)
const result = fn(1)
result // $ExpectType number
})
it('with two different explicit types', () => {
const fn = unless(
x => {
x // $ExpectType number
return x > 5
},
x => {
x // $ExpectType number
return `${x}-foo`
}
)
const result = fn(1)
result // $ExpectType string | number
})
})
```
[](#unless)
### unnest
Try this R.unnest example in Rambda REPL
[](#unnest)
### unwind
Try this R.unwind example in Rambda REPL
[](#unwind)
### update
```typescript
update(index: number, newValue: T, list: T[]): T[]
```
It returns a copy of `list` with updated element at `index` with `newValue`.
Try this R.update example in Rambda REPL
All TypeScript definitions
```typescript
update(index: number, newValue: T, list: T[]): T[];
update(index: number, newValue: T): (list: T[]) => T[];
```
R.update source
```javascript
import { cloneList } from './_internals/cloneList.js'
import { curry } from './curry.js'
export function updateFn(
index, newValue, list
){
const clone = cloneList(list)
if (index === -1) return clone.fill(newValue, index)
return clone.fill(
newValue, index, index + 1
)
}
export const update = curry(updateFn)
```
Tests
```javascript
import { update } from './update.js'
const list = [ 1, 2, 3 ]
test('happy', () => {
const newValue = 8
const index = 1
const result = update(
index, newValue, list
)
const curriedResult = update(index, newValue)(list)
const tripleCurriedResult = update(index)(newValue)(list)
const expected = [ 1, 8, 3 ]
expect(result).toEqual(expected)
expect(curriedResult).toEqual(expected)
expect(tripleCurriedResult).toEqual(expected)
})
test('list has no such index', () => {
const newValue = 8
const index = 10
const result = update(
index, newValue, list
)
expect(result).toEqual(list)
})
test('with negative index', () => {
expect(update(
-1, 10, [ 1 ]
)).toEqual([ 10 ])
expect(update(
-1, 10, []
)).toEqual([])
expect(update(
-1, 10, list
)).toEqual([ 1, 2, 10 ])
expect(update(
-2, 10, list
)).toEqual([ 1, 10, 3 ])
expect(update(
-3, 10, list
)).toEqual([ 10, 2, 3 ])
})
```
TypeScript test
```typescript
import {update} from 'rambda'
describe('R.update', () => {
it('happy', () => {
const result = update(1, 0, [1, 2, 3])
result // $ExpectType number[]
})
})
```
[](#update)
### values
```typescript
values(obj: T): T[K][]
```
With correct input, this is nothing more than `Object.values(Record)`. If `obj` is not an object, then it returns an empty array.
Try this R.values example in Rambda REPL
All TypeScript definitions
```typescript
values(obj: T): T[K][];
```
R.values source
```javascript
import { type } from './type.js'
export function values(obj){
if (type(obj) !== 'Object') return []
return Object.values(obj)
}
```
Tests
```javascript
import { values } from './values.js'
test('happy', () => {
expect(values({
a : 1,
b : 2,
c : 3,
})).toEqual([ 1, 2, 3 ])
})
test('with bad input', () => {
expect(values(null)).toEqual([])
expect(values(undefined)).toEqual([])
expect(values(55)).toEqual([])
expect(values('foo')).toEqual([])
expect(values(true)).toEqual([])
expect(values(false)).toEqual([])
expect(values(NaN)).toEqual([])
expect(values(Infinity)).toEqual([])
expect(values([])).toEqual([])
})
```
TypeScript test
```typescript
import {values} from 'rambda'
describe('R.values', () => {
it('happy', () => {
const result = values({
a: 1,
b: 2,
c: 3,
})
result // $ExpectType number[]
})
})
```
[](#values)
### view
```typescript
view(lens: Lens): (obj: S) => A
```
It returns the value of `lens` focus over `target` object.
Try this R.view example in Rambda REPL
All TypeScript definitions
```typescript
view(lens: Lens): (obj: S) => A;
view(lens: Lens, obj: S): A;
```
R.view source
```javascript
const Const = x => ({
x,
map : fn => Const(x),
})
export function view(lens, target){
if (arguments.length === 1) return _target => view(lens, _target)
return lens(Const)(target).x
}
```
Tests
```javascript
import { assoc } from './assoc.js'
import { lens } from './lens.js'
import { prop } from './prop.js'
import { view } from './view.js'
const testObject = { foo : 'Led Zeppelin' }
const assocLens = lens(prop('foo'), assoc('foo'))
test('happy', () => {
expect(view(assocLens, testObject)).toBe('Led Zeppelin')
})
```
[](#view)
### when
```typescript
when(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U
```
It pass `input` to `predicate` function and if the result is `true`, it will return the result of `whenTrueFn(input)`.
If the `predicate` returns `false`, then it will simply return `input`.
Try this R.when example in Rambda REPL
All TypeScript definitions
```typescript
when(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U;
when(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U): (input: T) => T | U;
when(predicate: (x: T) => boolean): ((whenTrueFn: (a: T) => U) => (input: T) => T | U);
```
R.when source
```javascript
import { curry } from './curry.js'
function whenFn(
predicate, whenTrueFn, input
){
if (!predicate(input)) return input
return whenTrueFn(input)
}
export const when = curry(whenFn)
```
Tests
```javascript
import { add } from './add.js'
import { when } from './when.js'
const predicate = x => typeof x === 'number'
test('happy', () => {
const fn = when(predicate, add(11))
expect(fn(11)).toBe(22)
expect(fn('foo')).toBe('foo')
})
```
TypeScript test
```typescript
import {when} from 'rambda'
const predicate = (x: number) => x > 2
const whenTrueFn = (x: number) => String(x)
describe('R.when', () => {
it('happy', () => {
const result = when(predicate, whenTrueFn, 1)
result // $ExpectType string | 1
})
it('curry 1', () => {
const fn = when(predicate, whenTrueFn)
const result = fn(1)
result // $ExpectType string | number
})
it('curry 2 require explicit types', () => {
const fn = when(predicate)(whenTrueFn)
const result = fn(1)
result // $ExpectType string | number
})
})
```
[](#when)
### where
```typescript
where(conditions: T, input: U): boolean
```
It returns `true` if all each property in `conditions` returns `true` when applied to corresponding property in `input` object.
Try this R.where example in Rambda REPL
All TypeScript definitions
```typescript
where(conditions: T, input: U): boolean;
where(conditions: T): (input: U) => boolean;
where(conditions: ObjFunc2, input: U): boolean;
where(conditions: ObjFunc2): (input: U) => boolean;
```
R.where source
```javascript
export function where(conditions, input){
if (input === undefined){
return _input => where(conditions, _input)
}
let flag = true
for (const prop in conditions){
if (!flag) continue
const result = conditions[ prop ](input[ prop ])
if (flag && result === false){
flag = false
}
}
return flag
}
```
Tests
```javascript
import { equals } from './equals.js'
import { where } from './where.js'
test('when true', () => {
const result = where({
a : equals('foo'),
b : equals('bar'),
},
{
a : 'foo',
b : 'bar',
x : 11,
y : 19,
})
expect(result).toBeTrue()
})
test('when false | early exit', () => {
let counter = 0
const equalsFn = expected => input => {
console.log(expected, 'expected')
counter++
return input === expected
}
const predicate = where({
a : equalsFn('foo'),
b : equalsFn('baz'),
})
expect(predicate({
a : 'notfoo',
b : 'notbar',
})).toBeFalse()
expect(counter).toBe(1)
})
```
TypeScript test
```typescript
import {where, equals} from 'rambda'
describe('R.where', () => {
it('happy', () => {
const input = {
a: 'foo',
b: 'bar',
x: 11,
y: 19,
}
const conditions = {
a: equals('foo'),
b: equals('bar'),
}
const result = where(conditions, input)
const curriedResult = where(conditions)(input)
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
})
```
[](#where)
### whereAny
Same as `R.where`, but it will return `true` if at least one condition check returns `true`.
Try this R.whereAny example in Rambda REPL
[](#whereAny)
### whereEq
```typescript
whereEq(condition: T, input: U): boolean
```
It will return `true` if all of `input` object fully or partially include `rule` object.
`R.equals` is used to determine equality.
Try this R.whereEq example in Rambda REPL
All TypeScript definitions
```typescript
whereEq(condition: T, input: U): boolean;
whereEq(condition: T): (input: U) => boolean;
```
R.whereEq source
```javascript
import { equals } from './equals.js'
import { filter } from './filter.js'
export function whereEq(condition, input){
if (arguments.length === 1){
return _input => whereEq(condition, _input)
}
const result = filter((conditionValue, conditionProp) =>
equals(conditionValue, input[ conditionProp ]),
condition)
return Object.keys(result).length === Object.keys(condition).length
}
```
Tests
```javascript
import { whereEq } from './whereEq.js'
test('when true', () => {
const condition = { a : 1 }
const input = {
a : 1,
b : 2,
}
const result = whereEq(condition, input)
const expectedResult = true
expect(result).toEqual(expectedResult)
})
test('when false', () => {
const condition = { a : 1 }
const input = { b : 2 }
const result = whereEq(condition, input)
const expectedResult = false
expect(result).toEqual(expectedResult)
})
test('with nested object', () => {
const condition = { a : { b : 1 } }
const input = {
a : { b : 1 },
c : 2,
}
const result = whereEq(condition)(input)
const expectedResult = true
expect(result).toEqual(expectedResult)
})
test('with wrong input', () => {
const condition = { a : { b : 1 } }
expect(() => whereEq(condition, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'a\')"')
})
```
TypeScript test
```typescript
import {whereEq} from 'rambda'
describe('R.whereEq', () => {
it('happy', () => {
const result = whereEq({a: {b: 2}}, {b: 2})
const curriedResult = whereEq({a: {b: 2}})({b: 2})
result // $ExpectType boolean
curriedResult // $ExpectType boolean
})
})
```
[](#whereEq)
### without
```typescript
without(matchAgainst: T[], source: T[]): T[]
```
It will return a new array, based on all members of `source` list that are not part of `matchAgainst` list.
`R.equals` is used to determine equality.
Try this R.without example in Rambda REPL
All TypeScript definitions
```typescript
without(matchAgainst: T[], source: T[]): T[];
without(matchAgainst: T[]): (source: T[]) => T[];
```
R.without source
```javascript
import { _indexOf } from './equals.js'
import { reduce } from './reduce.js'
export function without(matchAgainst, source){
if (source === undefined){
return _source => without(matchAgainst, _source)
}
return reduce(
(prev, current) =>
_indexOf(current, matchAgainst) > -1 ? prev : prev.concat(current),
[],
source
)
}
```
Tests
```javascript
import { without as withoutRamda } from 'ramda'
import { without } from './without.js'
test('should return a new list without values in the first argument', () => {
const itemsToOmit = [ 'A', 'B', 'C' ]
const collection = [ 'A', 'B', 'C', 'D', 'E', 'F' ]
expect(without(itemsToOmit, collection)).toEqual([ 'D', 'E', 'F' ])
expect(without(itemsToOmit)(collection)).toEqual([ 'D', 'E', 'F' ])
})
test('with list of objects', () => {
const itemsToOmit = [ { a : 1 }, { c : 3 } ]
const collection = [ { a : 1 }, { b : 2 }, { c : 3 }, { d : 4 } ]
const expected = [ { b : 2 }, { d : 4 } ]
expect(without(itemsToOmit, collection)).toEqual(expected)
expect(withoutRamda(itemsToOmit, collection)).toEqual(expected)
})
test('ramda accepts string as target input while rambda throws', () => {
expect(withoutRamda('0:1', [ '0', '0:1' ])).toEqual([ '0:1' ])
expect(() =>
without('0:1', [ '0', '0:1' ])).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of 0:1"')
expect(without([ '0:1' ], [ '0', '0:1' ])).toEqual([ '0' ])
})
test('ramda test', () => {
expect(without([ 1, 2 ])([ 1, 2, 1, 3, 4 ])).toEqual([ 3, 4 ])
})
```
TypeScript test
```typescript
import {without} from 'rambda'
const itemsToOmit = ['A', 'B', 'C']
const collection = ['A', 'B', 'C', 'D', 'E', 'F']
describe('R.without', () => {
it('happy', () => {
const result = without(itemsToOmit, collection)
result // $ExpectType string[]
})
it('curried', () => {
const result = without(itemsToOmit)(collection)
result // $ExpectType string[]
})
})
```
[](#without)
### xor
```typescript
xor(x: boolean, y: boolean): boolean
```
Logical XOR
Try this R.xor example in Rambda REPL
All TypeScript definitions
```typescript
xor(x: boolean, y: boolean): boolean;
xor(y: boolean): (y: boolean) => boolean;
```
R.xor source
```javascript
export function xor(a, b){
if (arguments.length === 1) return _b => xor(a, _b)
return Boolean(a) && !b || Boolean(b) && !a
}
```
Tests
```javascript
import { xor } from './xor.js'
test('compares two values with exclusive or', () => {
expect(xor(true, true)).toBeFalse()
expect(xor(true, false)).toBeTrue()
expect(xor(false, true)).toBeTrue()
expect(xor(false, false)).toBeFalse()
})
test('when both values are truthy, it should return false', () => {
expect(xor(true, 'foo')).toBeFalse()
expect(xor(42, true)).toBeFalse()
expect(xor('foo', 42)).toBeFalse()
expect(xor({}, true)).toBeFalse()
expect(xor(true, [])).toBeFalse()
expect(xor([], {})).toBeFalse()
expect(xor(new Date(), true)).toBeFalse()
expect(xor(true, Infinity)).toBeFalse()
expect(xor(Infinity, new Date())).toBeFalse()
})
test('when both values are falsy, it should return false', () => {
expect(xor(null, false)).toBeFalse()
expect(xor(false, undefined)).toBeFalse()
expect(xor(undefined, null)).toBeFalse()
expect(xor(0, false)).toBeFalse()
expect(xor(false, NaN)).toBeFalse()
expect(xor(NaN, 0)).toBeFalse()
expect(xor('', false)).toBeFalse()
})
test('when one argument is truthy and the other is falsy, it should return true', () => {
expect(xor('foo', null)).toBeTrue()
expect(xor(null, 'foo')).toBeTrue()
expect(xor(undefined, 42)).toBeTrue()
expect(xor(42, undefined)).toBeTrue()
expect(xor(Infinity, NaN)).toBeTrue()
expect(xor(NaN, Infinity)).toBeTrue()
expect(xor({}, '')).toBeTrue()
expect(xor('', {})).toBeTrue()
expect(xor(new Date(), 0)).toBeTrue()
expect(xor(0, new Date())).toBeTrue()
expect(xor([], null)).toBeTrue()
expect(xor(undefined, [])).toBeTrue()
})
```
TypeScript test
```typescript
import {xor} from 'rambda'
describe('R.xor', () => {
it('happy', () => {
xor(true, false) // $ExpectType boolean
})
it('curry', () => {
xor(true)(false) // $ExpectType boolean
})
})
```
[](#xor)
### zip
```typescript
zip(x: K[], y: V[]): KeyValuePair[]
```
It will return a new array containing tuples of equally positions items from both `x` and `y` lists.
The returned list will be truncated to match the length of the shortest supplied list.
Try this R.zip example in Rambda REPL
All TypeScript definitions
```typescript
zip(x: K[], y: V[]): KeyValuePair[];
zip(x: K[]): (y: V[]) => KeyValuePair[];
```
R.zip source
```javascript
export function zip(left, right){
if (arguments.length === 1) return _right => zip(left, _right)
const result = []
const length = Math.min(left.length, right.length)
for (let i = 0; i < length; i++){
result[ i ] = [ left[ i ], right[ i ] ]
}
return result
}
```
Tests
```javascript
import { zip } from './zip.js'
const array1 = [ 1, 2, 3 ]
const array2 = [ 'A', 'B', 'C' ]
test('should return an array', () => {
const actual = zip(array1)(array2)
expect(actual).toBeInstanceOf(Array)
})
test('should return and array or tuples', () => {
const expected = [
[ 1, 'A' ],
[ 2, 'B' ],
[ 3, 'C' ],
]
const actual = zip(array1, array2)
expect(actual).toEqual(expected)
})
test('should truncate result to length of shorted input list', () => {
const expectedA = [
[ 1, 'A' ],
[ 2, 'B' ],
]
const actualA = zip([ 1, 2 ], array2)
expect(actualA).toEqual(expectedA)
const expectedB = [
[ 1, 'A' ],
[ 2, 'B' ],
]
const actualB = zip(array1, [ 'A', 'B' ])
expect(actualB).toEqual(expectedB)
})
```
TypeScript test
```typescript
import {zip} from 'rambda'
describe('R.zip', () => {
it('happy', () => {
const array1 = [1, 2, 3]
const array2 = ['A', 'B', 'C']
const result = zip(array1)(array2)
result // $ExpectType KeyValuePair[]
})
})
```
[](#zip)
### zipObj
```typescript
zipObj(keys: K[], values: T[]): { [P in K]: T }
```
It will return a new object with keys of `keys` array and values of `values` array.
Try this R.zipObj example in Rambda REPL
All TypeScript definitions
```typescript
zipObj(keys: K[], values: T[]): { [P in K]: T };
zipObj(keys: K[]): (values: T[]) => { [P in K]: T };
zipObj(keys: K[], values: T[]): { [P in K]: T };
zipObj(keys: K[]): (values: T[]) => { [P in K]: T };
```
R.zipObj source
```javascript
import { take } from './take.js'
export function zipObj(keys, values){
if (arguments.length === 1) return yHolder => zipObj(keys, yHolder)
return take(values.length, keys).reduce((
prev, xInstance, i
) => {
prev[ xInstance ] = values[ i ]
return prev
}, {})
}
```
Tests
```javascript
import { equals } from './equals.js'
import { zipObj } from './zipObj.js'
test('zipObj', () => {
expect(zipObj([ 'a', 'b', 'c' ], [ 1, 2, 3 ])).toEqual({
a : 1,
b : 2,
c : 3,
})
})
test('0', () => {
expect(zipObj([ 'a', 'b' ])([ 1, 2, 3 ])).toEqual({
a : 1,
b : 2,
})
})
test('1', () => {
expect(zipObj([ 'a', 'b', 'c' ])([ 1, 2 ])).toEqual({
a : 1,
b : 2,
})
})
test('ignore extra keys', () => {
const result = zipObj([ 'a', 'b', 'c', 'd', 'e', 'f' ], [ 1, 2, 3 ])
const expected = {
a : 1,
b : 2,
c : 3,
}
expect(equals(result, expected)).toBeTrue()
})
```
TypeScript test
```typescript
import {zipObj} from 'rambda'
describe('R.zipObj', () => {
it('happy', () => {
// this is wrong since 24.10.2020 `@types/ramda` changes
const result = zipObj(['a', 'b', 'c', 'd'], [1, 2, 3])
;[result.a, result.b, result.c, result.d] // $ExpectType number[]
})
it('imported from @types/ramda', () => {
const result = zipObj(['a', 'b', 'c'], [1, 2, 3])
const curriedResult = zipObj(['a', 'b', 'c'])([1, 2, 3])
;[result.a, result.b, result.c] // $ExpectType number[]
;[curriedResult.a, curriedResult.b, curriedResult.c] // $ExpectType number[]
})
})
```
[](#zipObj)
### zipWith
```typescript
zipWith(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[]
```
Try this R.zipWith example in Rambda REPL
All TypeScript definitions
```typescript
zipWith(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[];
zipWith(fn: (x: T, y: U) => TResult, list1: T[]): (list2: U[]) => TResult[];
zipWith(fn: (x: T, y: U) => TResult): (list1: T[], list2: U[]) => TResult[];
```
R.zipWith source
```javascript
import { curry } from './curry.js'
import { take } from './take.js'
function zipWithFn(
fn, x, y
){
return take(x.length > y.length ? y.length : x.length, x).map((xInstance, i) => fn(xInstance, y[ i ]))
}
export const zipWith = curry(zipWithFn)
```
Tests
```javascript
import { add } from './add.js'
import { zipWith } from './zipWith.js'
const list1 = [ 1, 2, 3 ]
const list2 = [ 10, 20, 30, 40 ]
const list3 = [ 100, 200 ]
test('when second list is shorter', () => {
const result = zipWith(
add, list1, list3
)
expect(result).toEqual([ 101, 202 ])
})
test('when second list is longer', () => {
const result = zipWith(
add, list1, list2
)
expect(result).toEqual([ 11, 22, 33 ])
})
```
TypeScript test
```typescript
import {zipWith} from 'rambda'
const list1 = [1, 2]
const list2 = [10, 20, 30]
describe('R.zipWith', () => {
it('happy', () => {
const result = zipWith(
(x, y) => {
x // $ExpectType number
y // $ExpectType number
return `${x}-${y}`
},
list1,
list2
)
result // $ExpectType string[]
})
it('curried', () => {
const result = zipWith((x, y) => {
x // $ExpectType unknown
y // $ExpectType unknown
return `${x}-${y}`
})(list1, list2)
result // $ExpectType string[]
})
})
```
[](#zipWith)
## ❯ CHANGELOG
9.0.1
- Fix bad TS typings, due to missing declaration - [Issue #716](https://github.com/selfrefactor/rambda/issues/716)
9.0.0
Breaking change in TS definitions of `lenses` as now they are synced to `Ramda` types.
- Add `R.sortWith` - [Issue #707](https://github.com/selfrefactor/rambda/issues/707)
- Add `R.innerJoin`, `R.gt`, `R.gte`, `R.reduceBy`, `R.hasIn`
8.6.0
- Wrong typing for `R.dissocPath` - [Issue #709](https://github.com/selfrefactor/rambda/issues/709)
- Update build dependencies
8.5.0
- Revert changes in `R.anyPass` introduced in `8.4.0` release. The reason is that the change was breaking the library older than `5.2.0` TypeScript.
- Wrong `R.partial` TS definition - [Issue #705](https://github.com/selfrefactor/rambda/issues/705)
- Add `R.dropRepeatsBy`
- Add `R.empty`
- Add `R.eqBy`
- Add `R.forEachObjIndexed`
8.4.0
- Add `R.dissocPath`
- Fix TS definitions of `R.head/R.last` and add missing handle of empty string
- Add `R.removeIndex` - method was before only in `Rambdax`, but now since `R.dissocPath` is using it, it is added to main library.
- Allow `R.omit` to pass numbers as part of properties to omit, i.e. `R.omit(['a', 1], {a: {1: 1, 2: 2}})`
- R.keys always returns strings - [MR #700](https://github.com/selfrefactor/rambda/pull/700)
- Improve `R.prepend/R.append` type interference - [MR #699](https://github.com/selfrefactor/rambda/pull/699)
- Change `R.reduce` TS definitions so index is always received - [MR #696](https://github.com/selfrefactor/rambda/pull/696)
- Functions as a type guard in `R.anyPass` TS definitions - [MR #695](https://github.com/selfrefactor/rambda/pull/695)
- Fix R.append's curried type - [MR #694](https://github.com/selfrefactor/rambda/pull/694)
- Fix cannot compare errors in `Deno` with `R.equals` - [Issue #704](https://github.com/selfrefactor/rambda/issues/704).
- Fix cannot compare `BigInt` with `R.equals`
8.3.0
Add the following methods:
- binary
- call
- collectBy
- comparator
- composeWith
8.2.0
Add the following methods:
- addIndex
- addIndexRight
- ap
- aperture
- applyTo
- ascend
- descend
8.1.0
- Fix input order of TS definitions for `R.propEq` method - [Issue #688](https://github.com/selfrefactor/rambda/issues/688). The issue was due to 8.0.0 was shipped with TS definitions of `7.5.0` release.
- Add `R.differenceWith` method - [Issue #91](https://github.com/selfrefactor/rambdax/issues/91)
8.0.0
- handle falsy values in merge methods - https://github.com/ramda/ramda/pull/3222
- `R.head`/`R.last` don't return `undefined` for non-empty arrays
- `R.type` supports dates in TS definition - `Rambda` already did support dates in JS.
- Improve typings of `R.endsWith/startsWith` with regard to `string` input. - [PR #622](https://github.com/selfrefactor/rambda/pull/622)
- Handle list as falsy value in `R.reduce` - [Ramda MR](https://github.com/ramda/ramda/pull/2997/files)
- `R.nop` is removed - it will be moved to `Rambdax` as `R.noop`
- `R.includes` is no longer using string literal in TypeScript definitions
> Reason for breaking change - synchronize with Ramda `0.29.0` release:
- change order of `R.propEq` - [Ramda MR](https://github.com/ramda/ramda/pull/2938/files)
7.5.0
- IMPORTANT: Remove `export` property in `package.json` in order to allow `Rambda` support for projects with `"type": "module"` in `package.json` - [Issue #667](https://github.com/selfrefactor/rambda/issues/657)
- Add `R.unnest` - [Rambdax issue 89](https://github.com/selfrefactor/rambdax/issues/89)
- `R.uniq` is not using `R.equals` as Ramda does - [Issue #88](https://github.com/selfrefactor/rambdax/issues/88)
- Fix `R.path(['non','existing','path'], obj)` TS definition as 7.4.0 release caused TS errors - [Issue #668](https://github.com/selfrefactor/rambda/issues/668)
7.4.0
- Synchronize with `@types/ramda` - `R.prop`, `R.path`, `R.pickAll`
- Remove `esm` Rollup output due to tree-shaking issues.
- Upgrade all dev dependencies.
7.3.0
- Important - changing import declaration in `package.json` in order to fix tree-shaking issue - [Issue #647](https://github.com/selfrefactor/rambda/issues/647)
- Add `R.modify`
- Allow multiple inputs in TypeScript versions of `R.anyPass` and `R.allPass` - [Issue #642](https://github.com/selfrefactor/rambda/issues/604)
- Using wrong clone of object in `R.mergeDeepRight` - [Issue #650](https://github.com/selfrefactor/rambda/issues/650)
- Missing early return in `R.where` - [Issue #648](https://github.com/selfrefactor/rambda/issues/648)
- `R.allPass` doesn't accept more than 1 parameters for function predicates- [Issue #604](https://github.com/selfrefactor/rambda/issues/604)
7.2.1
- Remove bad typings of `R.propIs` which caused the library to cannot be build with TypeScript.
- Drop support for `Wallaby` as per [https://github.com/wallabyjs/public/issues/3037](https://github.com/wallabyjs/public/issues/3037)
7.2.0
- Wrong `R.update` if index is `-1` - [PR #593](https://github.com/selfrefactor/rambda/pull/593)
- Wrong curried typings in `R.anyPass` - [Issue #642](https://github.com/selfrefactor/rambda/issues/642)
- `R.modifyPath` not exported - [Issue #640](https://github.com/selfrefactor/rambda/issues/640)
- Add new method `R.uniqBy`. Implementation is coming from [Ramda MR#2641](https://github.com/ramda/ramda/pull/2641)
- Apply the following changes from `@types/rambda`:
-- [https://github.com/DefinitelyTyped/DefinitelyTyped/commit/bab47272d52fc7bb81e85da36dbe9c905a04d067](add `AnyFunction` and `AnyConstructor`)
-- Improve `R.ifElse` typings - https://github.com/DefinitelyTyped/DefinitelyTyped/pull/59291
-- Make `R.propEq` safe for `null/undefined` arguments - https://github.com/ramda/ramda/pull/2594/files
7.1.4
- `R.mergeRight` not found on `Deno` import - [Issue #633](https://github.com/selfrefactor/rambda/issues/633)
7.1.0
- Add `R.mergeRight` - introduced by Ramda's latest release. While Ramda renames `R.merge`, Rambda will keep `R.merge`.
- Rambda's `pipe/compose` doesn't return proper length of composed function which leads to issue with `R.applySpec`. It was fixed by using Ramda's `pipe/compose` logic - [Issue #627](https://github.com/selfrefactor/rambda/issues/627)
- Replace `Async` with `Promise` as return type of `R.type`.
- Add new types as TypeScript output for `R.type` - "Map", "WeakMap", "Generator", "GeneratorFunction", "BigInt", "ArrayBuffer"
- Add `R.juxt` method
- Add `R.propSatisfies` method
- Add new methods after `Ramda` version upgrade to `0.28.0`:
-- R.count
-- R.modifyPath
-- R.on
-- R.whereAny
-- R.partialObject
7.0.3
Rambda.none has wrong logic introduced in version `7.0.0` - [Issue #625](https://github.com/selfrefactor/rambda/issues/625)
7.0.2
Rambda doesn't work with `pnpm` due to wrong export configuration - [Issue #619](https://github.com/selfrefactor/rambda/issues/619)
7.0.1
- Wrong ESM export configuration in `package.json` - [Issue #614](https://github.com/selfrefactor/rambda/issues/614)
7.0.0
- Breaking change - sync `R.compose`/`R.pipe` with `@types/ramda`. That is significant change so as safeguard, it will lead a major bump. Important - this lead to raising required TypeScript version to `4.2.2`. In other words, to use `Rambda` you'll need TypeScript version `4.2.2` or newer.
Related commit in `@types/ramda` - https://github.com/DefinitelyTyped/DefinitelyTyped/commit/286eff4f76d41eb8f091e7437eabd8a60d97fc1f#diff-4f74803fa83a81e47cb17a7d8a4e46a7e451f4d9e5ce2f1bd7a70a72d91f4bc1
There are several other changes in `@types/ramda` as stated in [this comment](https://github.com/ramda/ramda/issues/2976#issuecomment-990408945). This leads to change of typings for the following methods in **Rambda**:
-- R.unless
-- R.toString
-- R.ifElse
-- R.always
-- R.complement
-- R.cond
-- R.is
-- R.sortBy
-- R.dissoc
-- R.toPairs
-- R.assoc
-- R.toLower
-- R.toUpper
- One more reason for the breaking change is changing of export declarations in `package.json` based on [this blog post](https://devblogs.microsoft.com/typescript/announcing-typescript-4-5-beta/#packagejson-exports-imports-and-self-referencing) and [this merged Ramda's PR](https://github.com/ramda/ramda/pull/2999). This also led to renaming of `babel.config.js` to `babel.config.cjs`.
- Add `R.apply`, `R.bind` and `R.unapply`
- `R.startsWith/R.endsWith` now support lists as inputs. This way, it matches current Ramda behavior.
- Remove unused typing for `R.chain`.
- `R.map`/`R.filter` no longer accept bad inputs as iterable. This way, Rambda behaves more like Ramda, which also throws.
- Make `R.lastIndexOf` follow the logic of `R.indexOf`.
- Change `R.type` logic to Ramda logic. This way, `R.type` can return `Error` and `Set` as results.
- Add missing logic in `R.equals` to compare sets - [Issue #599](https://github.com/selfrefactor/rambda/issues/599)
- Improve list cloning - [Issue #595](https://github.com/selfrefactor/rambda/issues/595)
- Handle multiple inputs with `R.allPass` and `R.anyPass` - [Issue #604](https://github.com/selfrefactor/rambda/issues/604)
- Fix `R.length` wrong logic with inputs as `{length: 123}` - [Issue #606](https://github.com/selfrefactor/rambda/issues/606).
- Improve non-curry typings of `R.merge` by using types from [mobily/ts-belt](https://github.com/mobily/ts-belt).
- Improve performance of `R.uniqWith`.
- Wrong `R.update` if index is `-1` - [PR #593](https://github.com/selfrefactor/rambda/pull/593)
- Make `R.eqProps` safe for falsy inputs - based on [this opened Ramda PR](https://github.com/ramda/ramda/pull/2943).
- Incorrect benchmarks for `R.pipe/R.compose` - [Issue #608](https://github.com/selfrefactor/rambda/issues/608)
- Fix `R.last/R.head` typings - [Issue #609](https://github.com/selfrefactor/rambda/issues/609)
6.9.0
- Fix slow `R.uniq` methods - [Issue #581](https://github.com/selfrefactor/rambda/issues/581)
Fixing `R.uniq` was done by improving `R.indexOf` which has performance implication to all methods importing `R.indexOf`:
- R.includes
- R.intersection
- R.difference
- R.excludes
- R.symmetricDifference
- R.union
- R.without no longer support the following case - `without('0:1', ['0', '0:1']) // => ['0']`. Now it throws as the first argument should be a list, not a string. Ramda, on the other hand, returns an empty list - https://github.com/ramda/ramda/issues/3086.
6.8.3
- Fix TypeScript build process with `rambda/immutable` - [Issue #572](https://github.com/selfrefactor/rambda/issues/572)
- Add `R.objOf` method
- Add `R.mapObjIndexed` method
- Publish shorter README.md version to NPM
6.8.0
- `R.has` use `Object.prototype.hasOwnProperty`- [Issue #572](https://github.com/selfrefactor/rambda/issues/572)
- Expose `immutable.ts` typings which are Rambda typings with `readonly` statements - [Issue #565](https://github.com/selfrefactor/rambda/issues/565)
- Fix `R.intersection` wrong order compared to Ramda.
- `R.path` wrong return of `null` instead of `undefined` when path value is `null` - [PR #577](https://github.com/selfrefactor/rambda/pull/577)
6.7.0
- Remove `ts-toolbelt` types from TypeScript definitions. Most affected are the following methods, which lose one of its curried definitions:
1. R.maxBy
2. R.minBy
3. R.pathEq
4. R.viewOr
5. R.when
6. R.merge
7. R.mergeDeepRight
8. R.mergeLeft
6.6.0
- Change `R.piped` typings to mimic that of `R.pipe`. Main difference is that `R.pipe` is focused on unary functions.
- Fix wrong logic when `R.without` use `R.includes` while it should use array version of `R.includes`.
- Use uglify plugin for UMD bundle.
- Remove `dist` folder from `.gitignore` in order to fix `Deno` broken package. [Issue #570](https://github.com/selfrefactor/rambda/issues/570)
- Improve `R.fromPairs` typings - [Issue #567](https://github.com/selfrefactor/rambda/issues/567)
6.5.3
- Wrong logic where `R.without` use `R.includes` while it should use the array version of `R.includes`
This is Ramda bug, that Rambda also has before this release - https://github.com/ramda/ramda/issues/3086
6.5.2
- Wrong `R.defaultTo` typings - changes introduced in v6.5.0 are missing their TS equivalent.
- Update dependencies
6.5.1
Fix wrong versions in changelog
6.5.0
- `R.defaultTo` no longer accepts infinite inputs, thus it follows Ramda implementation.
- `R.equals` supports equality of functions.
- `R.pipe` doesn't use `R.compose`.
- Close [Issue #561](https://github.com/selfrefactor/rambda/issues/561) - export several internal TS interfaces and types
- Close [Issue #559](https://github.com/selfrefactor/rambda/issues/559) - improve `R.propOr` typings
- Add `CHANGELOG.md` file in release files list
> This is only part of the changelog. You can read the full text in [CHANGELOG.md](CHANGELOG.md) file.
[](#-changelog)
## ❯ Additional info
> Most influential contributors(in alphabetical order)
-  [@farwayer](https://github.com/farwayer) - improving performance in R.find, R.filter; give the idea how to make benchmarks more reliable;
-  [@thejohnfreeman](https://github.com/thejohnfreeman) - add R.assoc, R.chain;
-  [@peeja](https://github.com/peeja) - add several methods and fix mutiple issues; provides great MR documentation
-  [@helmuthdu](https://github.com/helmuthdu) - add R.clone; help improve code style;
-  [@jpgorman](https://github.com/jpgorman) - add R.zip, R.reject, R.without, R.addIndex;
-  [@ku8ar](https://github.com/ku8ar) - add R.slice, R.propOr, R.identical, R.propIs and several math related methods; introduce the idea to display missing Ramda methods;
-  [@romgrk](https://github.com/romgrk) - add R.groupBy, R.indexBy, R.findLast, R.findLastIndex;
-  [@squidfunk](https://github.com/squidfunk) - add R.assocPath, R.symmetricDifference, R.difference, R.intersperse;
-  [@synthet1c](https://github.com/synthet1c) - add all lenses methods; add R.applySpec, R.converge;
-  [@vlad-zhukov](https://github.com/vlad-zhukov) - help with configuring Rollup, Babel; change export file to use ES module exports;
> Rambda references
- [Interview with Dejan Totef at SurviveJS blog](https://survivejs.com/blog/rambda-interview/)
- [Awesome functional Javascript programming libraries](https://github.com/stoeffel/awesome-fp-js#libraries)
- [Overview of Rambda pros/cons](https://mobily.github.io/ts-belt/docs/#rambda-%EF%B8%8F)
> Links to Rambda
- [https://github.com/stoeffel/awesome-fp-js](awesome-fp-js)
- [ https://mailchi.mp/webtoolsweekly/web-tools-280 ]( Web Tools Weekly #280 )
- [https://github.com/docsifyjs/awesome-docsify](awesome-docsify)
> Deprecated from `Used by` section
- [SAP's Cloud SDK](https://github.com/SAP/cloud-sdk) - This repo doesn't uses `Rambda` since *October/2020* [commit that removes Rambda](https://github.com/SAP/cloud-sdk/commit/b29b4f915c4e4e9c2441e7b6b67cf83dac1fdac3)
[](#-additional-info)
## My other libraries
Niketa theme
Collection of 9 light VSCode themes
Niketa dark theme
Collection of 9 dark VSCode themes
String-fn
String utility library
Useful Javascript libraries
Large collection of JavaScript,TypeScript and Angular related repos links
Run-fn
CLI commands for lint JS/TS files, commit git changes and upgrade of dependencies
## Stargazers over time
[](https://starchart.cc/selfrefactor/rambda)