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https://github.com/arccoza/iterly

Composable iterator and async iterator tools, supporting old platforms without yield or async/await
https://github.com/arccoza/iterly

async async-iterable async-iterator asynciterator composable iterable iterator no-dependencies zero-dependencies

Last synced: about 1 month ago
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Composable iterator and async iterator tools, supporting old platforms without yield or async/await

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# Description



An iterator / async-iterator library with support for old platforms that don't have iterables or async-iterables.

Iterly provides several useful functions for composing, manipulating and iterating through iterables,

async-iterables, arrays, streams, and array-like objects such as nodejs Buffer.



Even though iterly doesn't use async functions or generators, and should work on browsers as far back as ie10,

you will still need to pass your code through Babel or similar to transpile modern syntax used in this library,

such as destructuring.



# Install



`yarn add iterly` or `npm install iterly`



# API



### Table of Contents



-   Iteration helpers

    -   [each](#each)

    -   [iter](#iter)

    -   [iterArray](#iterarray)

    -   [iterObject](#iterobject)

    -   [iterFn](#iterfn)

-   Function composition

    -   [compose](#compose)

    -   [curry](#curry)

-   Sync operators

    -   [map](#map)

    -   [reduce](#reduce)

    -   [filter](#filter)

-   Async operators

    -   [amap](#amap)

    -   [areduce](#areduce)

    -   [afilter](#afilter)

-   Sync / Async operators

    -   [enumerate](#enumerate)

-   [Range](#range)

-   [range](#range-1)



## each



Loops over any iterable, async-iterable, iterator, async-iterator or array-like,

calling fn for each item. If looping over an async-iterable / async-iterator

a promise will be returned by each with the value of the final return from fn.



### Parameters



-   `x` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The number of async items to run in parallel, has no effect on sync iterables. (optional, default `1`)

-   `fn` **(function (value) | function (value, done))** The fn to call for each item. The function will be called

    for every value in the iterable / async-iterable. If the function has a second param (done) then

    the loop function will be called when the iterable / async-iterable is done, with a done value of true.

    If no second param (done) is provided then the loop function will only be called with the values from

    the iterable / async-iterable.

-   `it` **(iterable | asyncIterable)** The iterable, async-iterable, iterator, async-iterator or array-like

    to loop over.



### Examples



```javascript

each((value) => console.log(value), [1, 2, 3, 4])

// Will print:

// 1

// 2

// 3

// 4

```



Returns **([Promise](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Promise) \| [undefined](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/undefined))** Returns a Promise that resolves to the last value returned by fn if looping

over an async-iterable. If looping over an iterable returns undefined.



## iter



Gets an iterator / async-iterator for any iterable, async-iterable, array-like, or function with a sentinel.



### Parameters



-   `obj` **[Object](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object)** The possible iterable to create an iterator for.

-   `options` **[Object](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object)**  (optional, default `{}`)

    -   `options.sentinel`  Any distinct value to use as a stop indicator when creating an iterator from a function,

        see iterFn.

    -   `options.isAsync` **[Boolean](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean)** If true and obj is a function, an async-iterator will be returned. (optional, default `false`)



Returns **(@@iterator | @@asyncIterator | [undefined](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/undefined))** Returns an iterator, async-iterator, or undefined if obj is not iterable.



## iterArray



Gets an iterator for any array-like; that is anything with a length property that

can be indexed with array[index] notation.



### Parameters



-   `a` **([Array](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array) | arrayLike)** The array-like to create an iterator from.

-   `chunkSize` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** If set larger than zero, will break the array up

    into chunks of length chunkSize. (optional, default `0`)



### Examples



```javascript

var it = iterArray([1, 2, 3, 4])

// Will give you an iterator with the values: 1, 2, 3, 4

var it = iterArray([1, 2, 3, 4], 2)

// Will give you an iterator with the values: [1, 2], [3, 4]

```



Returns **@@iterator** Returns an iterator with the values from the array-like.



## iterObject



Gets an iterator of [key, value] pairs for any javascript object.



### Parameters



-   `o` **[Object](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object)** The object to create an iterator from. Only iterates over an objects own-properties.



### Examples



```javascript

var it = iterObject({a: 1, b: 2, c: 3})

// Will give you an iterator with the values: [a, 1], [b, 2], [c, 3]

```



Returns **@@iterator** Returns an iterator with the [key, value] pairs from the object.



## iterFn



Turns a function into an iterator.



### Parameters



-   `fn` **function ({i, sentinel})** The iterator will return whatever this function returns,

    until it returns the sentinel value, then it will stop. The function is given an object with

    an index i and the sentinel value, you can add any other state you want to keep between iterations

    to this object if you like.

-   `options` **[Object](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object)** This options object must contain the sentinel property, the sentinel

    is returned by fn to signal the end of iteration.

    -   `options.sentinel`  Any distinct value to use as an indicator that the iterator function is done.

    -   `options.isAsync` **[Boolean](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean)** If true an async-iterator will be returned. (optional, default `false`)



### Examples



```javascript

var it = iterFn(({i, sentinel}) => i >= 4 ? sentinel : i * 2, {sentinel: {}})

// Will give you an iterator with the values: 0, 2, 4, 6

```



Returns **(@@iterator | @@asyncIterator)** Returns an iterator or async-iterator with the values returned by fn.



## compose



Perhaps the most useful function here; allows you to compose (combine)

other functions into one new function that takes one argument of

an iterable, async-iterable, iterator, or async-iterator.



### Parameters



-   `fns` **...[function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)** Any number of functions to combine.



### Examples



```javascript

var urlPrefix = 'http://some.resource.com/'

var files = ['file.txt', 'file2.txt', 'file3.txt', 'file4.txt']



var getShortTexts = compose(

  filter.curry(file => file != 'file3.txt'), // Removes file3.txt

  map.curry(file => urlPrefix + file), // Adds the url prefix to the file names, creating the file url

  amap.curry(url => fetch(url).then(res => res.text())), // Fetches the files from the web

  afilter.curry(txt => txt.length <= 140), // Removes files longer than 140 characters

)



each(txt => console.log(txt), getShortTexts([files]))

// Will print out the contents of the files with 140 or fewer chracters, skipping file3.txt.

```



Returns **function (it: anyIterableOrAsyncIterable)** The composed function.



## curry



Returns a curried version of the provided function.



### Parameters



-   `fn` **[function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)** The function to curry.

-   `args` **...any?** Any arguments to bind.



Returns **[function](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Statements/function)** Returns the curried function.



## map



A function that maps iterator or iterable values over a function.



### Parameters



-   `fn` **function (value: any, index: [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number))** The function to modify each value in the iterator.

-   `it` **@@iterator** The iterator or iterable to map over.



### Examples



```javascript

var it = map(v => 2 * v, [1, 2, 3, 4])

// Will give you an iterator with the values: 2, 4, 6, 8

```



Returns **@@iterator** Returns an iterator with values that will be updated by fn.



### curry



Allows you to curry the arguments, most useful when used with compose.



#### Parameters



-   `args` **...any** The arguments to bind.



#### Examples



```javascript

var curried = map.curry(v => 2 * v)

var it = [1, 2, 3, 4]

it = curried(it)

// Will give you an iterator with the values: 2, 4, 6, 8

```



Returns **curriedFunction** The curried version of the original function, with bindable args.



## reduce



A function that reduces all the items in an iterator or iterable to one value.



### Parameters



-   `fn` **function (accumulator: any, value: any, index: [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number))** The reducer function continually updates

    the accumulator, until the iterator ends, then the accumulated value is returned.

-   `acc`  The accumulator's initial value, each item in the iterator or iterable will be added to this by fn.

-   `it` **@@iterator** The iterator or iterable to reduce.



### Examples



```javascript

var it = reduce((acc, v) => acc += v, 0, [1, 2, 3, 4])

// Will give you an iterator with the value: 10

var it = reduce((acc, v, i) => (acc[i] = v, acc), [], [1, 2, 3, 4])

// Will give you an iterator with a single item, which will be an array: [1, 2, 3, 4]

```



Returns **@@iterator** Returns an iterator with only one value.



### curry



Allows you to curry the arguments, most useful when used with compose.



#### Parameters



-   `args` **...any** The arguments to bind.



#### Examples



```javascript

var curried = reduce.curry((acc, val) => acc + val)

var it = [1, 2, 3, 4]

it = curried(it)

// Will give you an iterator with the value: 10

```



Returns **curriedFunction** The curried version of the original function, with bindable args.



## filter



A function that keeps values in an iterator or iterable only if fn returns true.



### Parameters



-   `fn` **function (value: any, index: [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number))** The test function to filter items,

    return true to keep the item, false to remove it.

-   `it` **@@iterator** The iterator or iterable to filter.



### Examples



```javascript

var it = filter(v => v != 2, [1, 2, 3, 4])

// Will give you an iterator with the values: 1, 3, 4

```



Returns **@@iterator** Returns an iterator with only the values that passed the test fn.



### curry



Allows you to curry the arguments, most useful when used with compose.



#### Parameters



-   `args` **...any** The arguments to bind.



#### Examples



```javascript

var curried = filter.curry(v => v != 2)

var it = [1, 2, 3, 4]

it = curried(it)

// Will give you an iterator with the values: 1, 3, 4

```



Returns **curriedFunction** The curried version of the original function, with bindable args.



## amap



A function that maps iterator, iterable, async-iterator or async-iterable values over a function.



### Parameters



-   `fn` **function (value: any, index: [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number))** The function to modify each value in the iterator.

-   `it` **(@@iterator | @@asyncIterator)** The iterator, iterable, async-iterator or async-iterable to map over.



### Examples



```javascript

var it = amap(v => 2 * v, [1, 2, 3, 4])

// Will give you an async-iterator with the promised values: 2, 4, 6, 8



var urls = ['http://some.resource.com/file.txt', 'http://some.resource.com/file2.txt']

var it = amap(url => fetch(url).then(res => res.text()), urls)

it = amap(txt => txt.slice(0, 140), it)

each(txt => console.log(txt), it)

// Will print the first 140 characters of text for each file referenced by the urls

```



Returns **@@asyncIterator** Returns an async-iterator with values returned by fn.



### curry



Allows you to curry the arguments, most useful when used with compose.



#### Parameters



-   `args` **...any** The arguments to bind.



#### Examples



```javascript

var curried = amap.curry(v => 2 * v)

var it = [1, 2, 3, 4]

it = curried(it)

// Will give you an async-iterator with the promised values: 2, 4, 6, 8

```



Returns **curriedFunction** The curried version of the original function, with bindable args.



## areduce



A function that reduces an iterator, iterable, async-iterator or async-iterable to one promised value.



### Parameters



-   `n` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** If a value greater than 0 is provided, then areduce will create multiple,

    grouped reductions, each made of `n` items, like a scan fn. (optional, default `0`)

-   `fn` **function (accumulator: any, value: any, index: [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number))** The reducer function continually updates

    the accumulator, until the iterator / async-iterator ends, then the accumulated value is returned.

-   `acc`  The accumulator's initial value, each item in the iterator or iterable will be added to this by fn.

-   `it` **(@@iterator | @@asyncIterator)** The iterator, iterable, async-iterator or async-iterable to reduce.



### Examples



```javascript

var it = areduce((acc, v) => acc += v, 0, [1, 2, 3, 4])

// Will give you an async-iterator with the promised value: 10



var urls = ['http://some.resource.com/file.txt', 'http://some.resource.com/file2.txt']

var it = amap(url => fetch(url).then(res => res.text()), urls)

it = areduce((acc, txt) => acc + txt.slice(0, 140), '', it)

each(txt => console.log(txt), it)

// Will print the combined 280 characters of text from each file referenced by the urls

```



Returns **@@asyncIterator** Returns an async-iterator with only one promised value.



### curry



Allows you to curry the arguments, most useful when used with compose.



#### Parameters



-   `args` **...any** The arguments to bind.



#### Examples



```javascript

var curried = areduce.curry((acc, val) => acc + val)

var it = [1, 2, 3, 4]

it = curried(it)

// Will give you an async-iterator with the promised value: 10

```



Returns **curriedFunction** The curried version of the original function, with bindable args.



## afilter



A function that keeps values in an iterator, iterable, async-iterator or async-iterable,

only if fn returns true.



### Parameters



-   `fn` **function (value: any, index: [number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number))** The test function to filter items,

    return true to keep the item, false to remove it.

-   `it` **(@@iterator | @@asyncIterator)** The iterator, iterable, async-iterator or async-iterable to filter.



### Examples



```javascript

var it = afilter(v => v != 2, [1, 2, 3, 4])

// Will give you an async-iterator with the promised values: 1, 3, 4



var urls = ['http://some.resource.com/file.txt', 'http://some.resource.com/file2.txt']

var it = amap(url => fetch(url).then(res => res.text()), urls)

it = afilter(txt => txt.length < 140, it)

each(txt => console.log(txt), it)

// Will only print the text of the files, referenced by the urls, with fewer than 140 characters

```



Returns **@@asyncIterator** Returns an async-iterator with the values that passed the test fn.



### curry



Allows you to curry the arguments, most useful when used with compose.



#### Parameters



-   `args` **...any** The arguments to bind.



#### Examples



```javascript

var curried = afilter.curry(v => v != 2)

var it = [1, 2, 3, 4]

it = curried(it)

// Will give you an async-iterator with the promised values: 1, 3, 4

```



Returns **curriedFunction** The curried version of the original function, with bindable args.



## enumerate



Enumerate takes an iterable, async-iterable, iterator, or async-iterator

and returns the same with its values updated with an [index, value] pair,

starting at 0 or at the optional start arg.



### Parameters



-   `start` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The optional index start. (optional, default `0`)

-   `it` **(iterable | asyncIterable)** The iterable or async-iterable to return.



### Examples



```javascript

var arr = ['a', 'b', 'c', 'd']

var it = enumerate(arr)

// Will give you an iterator with the values: [0, 'a'], [1, 'b'], [2, 'c'], [3, 'd']

```



Returns **(iterator | asyncIterator)** Returns an iterator or async-iterator with

the [index, value] pair items.



## Range



Creates a Range object that can be iterated over.



### Parameters



-   `start` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The start of the range (inclusive). (optional, default `0`)

-   `stop` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The end of the range (exclusive).

-   `step` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The stride of the range. (optional, default `1`)



Returns **[Range](#range)** 



### ITERATOR



Creates an iterator of all the values in the range.



Returns **Iterator** 



### values



Creates an iterator of all the values in the range.



Returns **Iterator** 



### entries



Creates an iterator of all the entries in the range.



Returns **Iterator** Returns value pairs [value, value], like Set.



### get



Get an item from a range by index.



#### Parameters



-   `idx` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The index of the value in the range.



Returns **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** Returns the value at the index, or undefined.



### has



Check if a value exists in a range.



#### Parameters



-   `val` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The value to look for.



Returns **[boolean](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean)** Returns true if the value exists.



### indexOf



Find the index of a value in the range.



#### Parameters



-   `val` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The value to look for.



Returns **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** Returns the index if the value exists, -1 otherwise.



### new



An alternative, static method, Range constructor.



#### Parameters



-   `start` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The start of the range (inclusive). (optional, default `0`)

-   `stop` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The end of the range (exclusive).

-   `step` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The stride of the range. (optional, default `1`)



Returns **[Range](#range)** 



## range



An alternative, functional, Range constructor.



### Parameters



-   `start` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The start of the range (inclusive). (optional, default `0`)

-   `stop` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The end of the range (exclusive).

-   `step` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** The stride of the range. (optional, default `1`)



Returns **[Range](#range)**