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
  • iter
  • iterArray
  • iterObject
  • iterFn
• Function composition
  • compose
  • curry
• Sync operators
  • map
  • reduce
  • filter
• Async operators
  • amap
  • areduce
  • afilter
• Sync / Async operators
  • enumerate
• Range
• range

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 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

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

Returns (Promise | 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 The possible iterable to create an iterator for.
• options 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 If true and obj is a function, an async-iterator will be returned. (optional, default false)

Returns (@@iterator | @@asyncIterator | 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 | arrayLike) The array-like to create an iterator from.
• chunkSize number If set larger than zero, will break the array up into chunks of length chunkSize. (optional, default 0)

Examples

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 The object to create an iterator from. Only iterates over an objects own-properties.

Examples

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 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 If true an async-iterator will be returned. (optional, default false)

Examples

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 Any number of functions to combine.

Examples

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 The function to curry.
• args ...any? Any arguments to bind.

Returns function Returns the curried function.

map

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

Parameters

• fn function (value: any, index: number) The function to modify each value in the iterator.
• it @@iterator The iterator or iterable to map over.

Examples

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

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) 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

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

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) 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

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

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) The function to modify each value in the iterator.
• it (@@iterator | @@asyncIterator) The iterator, iterable, async-iterator or async-iterable to map over.

Examples

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

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 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) 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

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

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) 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

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

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 The optional index start. (optional, default 0)
• it (iterable | asyncIterable) The iterable or async-iterable to return.

Examples

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 The start of the range (inclusive). (optional, default 0)
• stop number The end of the range (exclusive).
• step number The stride of the range. (optional, default 1)

Returns 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 The index of the value in the range.

Returns number Returns the value at the index, or undefined.

has

Check if a value exists in a range.

Parameters

• val number The value to look for.

Returns boolean Returns true if the value exists.

indexOf

Find the index of a value in the range.

Parameters

• val number The value to look for.

Returns number Returns the index if the value exists, -1 otherwise.

new

An alternative, static method, Range constructor.

Parameters

• start number The start of the range (inclusive). (optional, default 0)
• stop number The end of the range (exclusive).
• step number The stride of the range. (optional, default 1)

Returns Range

range

An alternative, functional, Range constructor.

Parameters

• start number The start of the range (inclusive). (optional, default 0)
• stop number The end of the range (exclusive).
• step number The stride of the range. (optional, default 1)

Returns Range