https://github.com/oaxoa/fp-filters
A curated list of ready-to-use (functional programming) array filters (TS / ESM / CJS)
https://github.com/oaxoa/fp-filters
array-filters filter filtering filters fp functional-programming predicates
Last synced: 4 months ago
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A curated list of ready-to-use (functional programming) array filters (TS / ESM / CJS)
- Host: GitHub
- URL: https://github.com/oaxoa/fp-filters
- Owner: Oaxoa
- License: mit
- Created: 2023-06-20T11:16:28.000Z (almost 3 years ago)
- Default Branch: master
- Last Pushed: 2025-09-11T07:09:11.000Z (9 months ago)
- Last Synced: 2025-12-20T03:20:51.104Z (6 months ago)
- Topics: array-filters, filter, filtering, filters, fp, functional-programming, predicates
- Language: TypeScript
- Homepage:
- Size: 2.06 MB
- Stars: 86
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
Awesome Lists containing this project
README
# fp-filters
[](https://github.com/oaxoa/fp-filters/actions/workflows/build.yml) [](https://codecov.io/gh/Oaxoa/fp-filters)
A curated collection of 130+ common-use filter functions that are written (and can be used) in a functional programming
style.
- GitHub: https://github.com/Oaxoa/fp-filters
- NPM: https://www.npmjs.com/package/fp-filters
- Docs: https://oaxoa.github.io/fp-filters/
## 🧠 How is this helpful?
_fp-filters_ allows you to stop rewriting the same code over and over again and greatly improves readability.
So that you will probably never write another filter function 🚀!
## Import
All the functions are grouped by semantics and individually exported.
E.g.:
```js
// ...
import { isEven } from 'fp-filters/number/isEven.js';
import { is } from 'fp-filters/misc/is.js';
import { isTrue } from 'fp-filters/boolean/isTrue.js';
import { isPastDate } from 'fp-filters/date/isPastDate.js';
import { hasProps } from 'fp-filters/object/hasProps.js';
// ...
```
Therefore, they must be individually imported.
No barrel files or entry points guarantees that you will not import what you don't use.
## 🔎 Examples
A few random examples of the 130+ functions available in _fp-filters_. Grouped by semantic.
See full docs here: [https://oaxoa.github.io/fp-filters/](https://oaxoa.github.io/fp-filters/)
### Booleans
```js
// without fp-filters
array.filter((arg) => arg === true);
// with fp-filters
array.filter(isTrue);
```
### Dates
```js
// without fp-filters
dates.filter((date) => {
const day = date.getDay();
return day === 0 || day === 6;
});
// with fp-filters
dates.filter(isWeekend);
```
### Lengths
```js
// without fp-filters
array.filter((arg) => arg.length > 0);
// with fp-filters
array.filter(isNotEmpty);
```
### Misc
```js
// without fp-filters
ids.filter((id) => id === currentUserId);
// with fp-filters
ids.filter(is(currentUserId));
```
### Numbers
```js
// without fp-filters
scores.filter((value) => value !== 0);
// with fp-filters
scores.filter(isNotZero);
```
```js
// without fp-filters
array.filter((arg) => arg % 2 === 0);
// with fp-filters
array.filter(isEven);
```
```js
// without fp-filters
array.filter((arg) => arg >= 10 && arg <= 50);
// with fp-filters
array.filter(isBetween(10, 50));
```
### Objects
```js
// without fp-filters
products.filter((obj) => obj.id !== undefined && obj.plu !== undefined);
// with fp-filters
products.filter(hasProps(['id', 'plu']));
```
```js
// without fp-filters
products.find((obj) => obj.country === countryId && obj.plu === plu);
// with fp-filters
products.find(hasProps(['country', 'plu'], [countryId, plu]));
```
```js
// without fp-filters
array.filter((obj) => obj.id === someOtherObj.id && obj.brand === someOtherObj.brand);
// with fp-filters
array.filter(hasSameProps(someOtherObj, ['id', 'brand']));
```
### Positions
```js
// without fp-filters
array.filter((arg, index) => index % 3 === 1 || index % 3 === 2);
// with fp-filters
array.filter(pattern(false, true, true));
```
```js
// without fp-filters
array.filter((arg, index) => index % 3 === 1);
// with fp-filters
array.filter(isEveryNthIndex(3, 1));
```
### Strings
```js
// without fp-filters
array.filter((arg) => arg === '');
// with fp-filters
array.filter(isEmptyString);
```
```js
// without fp-filters
array.filter((arg: string) => {
for (let i = 0; i < arg.length / 2; i++) {
if (arg[i] !== arg[arg.length - i - 1]) {
return false;
}
}
return true;
});
// with fp-filters
array.filter(isPalindrome);
```
### Types
```js
// without fp-filters
array.filter((arg) => arg !== undefined);
// with fp-filters
array.filter(isNotUndefined);
```
```js
// without fp-filters
array.filter((arg) => typeof arg === 'boolean');
// with fp-filters
array.filter(isBoolean);
// do not be tricked by `array.filter(Boolean);`. It is different as
// it casts the content and then evaluate its truthyness
```
### Arrays
```js
const input = [[1, 2, 3], [2, 4], [0, 4, 8, 16]];
// without fp-filters
input.filter((array) => array.every((element) => element % 2 === 0));
// with fp-filters
input.filter(everyElement(isEven))
```
## ❗ Negate or 🧩 combine filters
Most of the functions include aliases for their negated versions (
using [fp-booleans](https://npmjs.org/package/fp-booleans)):
```js
// E.g.:
array.filter(is(5))
array.filter(isNot(5))
array.filter(isBetween(5, 10))
array.filter(isNotBetween(5, 10))
array.filter(isEmpty)
array.filter(isNotEmpty)
array.filter(isInstanceOf(SomeClass));
array.filter(isNotInstanceOf(SomeClass));
```
but **you can make your own**.
> _fp-filters_ leaverages _fp-booleans_'s very powerful functions to combine or negate functions
some examples:
```js
import { not, and, or } from 'fp-booleans';
const isNot = not(is);
array.filter(isNot(5));
const canBeDiscounted = (minPrice) => and(isGreaterOrEqualTo(minPrice), not(isRound));
array.filter(canBeDiscounted(10));
const isValidAdmin = or(is('admin'), and(startsWith('user_'), isLowerCase))
array.filter(isValidAdmin);
```
## 🧑🏼💻 Coding style
fp-filters functions are predicates. Just like array filters are.
They get arguments and return a boolean.
They can be used as such. But they shine when used as filters.
fp-filters functions are:
### ✨ Pure
All are pure. Some are higher-order and unlocks the power of partial application in filters.
### 🤏🏼 Tiny
Most are one-liners. The longest is ~10 lines.
### 🧱 Composable
Higher-order predicates and fp-booleans unleash quite some power
### 🪆 Zero-ish dependencies
Most of them have zero deps. Some of them have 1 dependency on fp-booleans (that has zero deps).
No surprises.
### 🍃 More than tree-shakeable.
No barrel files, or entry points.
You import and bundle only what you use. No way to mess it up.
If you use one function only, that's what goes in your bundle. The cost of it is in bytes.
> Just as it would cost to write the function yourself. But with free 100% coverage testing, types, docs and no risk of
> duplicated code.
### 🗂️ Grouped semantically
Functions for numbers, functions for strings, you get the point.
So you will always intuitively know where to find the one you need.
### ✅ 100% tested by design
Yes, all of them are tested. Every branch, every line.
130+ stable unit tests running in less than 1s.
> Functions that are partial applications of other 100% tested functions (from fp-filters or fp-booleans) are
> not tested. On purpose.
### ✏️ Typescript typed
All functions are fully typed. No `any` type, some `unknown`. Working on it. Help is appreciated ❤️.
## 🚀 Getting started
### 💻 Installation
fp-filters runs on Node.js and is available as a NPM package.
```bash
npm install --save fp-filters
```
or
```bash
yarn add fp-filters
```
## 🤝 Contributions
1. [Coding style](#%F0%9F%A7%91%F0%9F%8F%BC%F0%9F%92%BB-coding-style)
1. [Contributing guide](CONTRIBUTING.md)
1. [Code of Conduct](CODE_OF_CONDUCT.md)
## 📜 License & Copyrights
[MIT](https://opensource.org/licenses/MIT)
Copyright (c) 2023-present, Pierluigi Pesenti (Oaxoa)