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By Kirill Boychenko - Sep 24, 2025
@nkp/iterable
Advanced tools
@nkp/iterable
Iteration utility for synchronous iterators like arrays, sets, maps and generators.
@nkp/iterable
Immutable collection utility classes for synchronous and lazy iteration over iterables like arrays, sets, maps and generators.
@nkp/iterable exposes two main utility classes, Collection and LazyCollection.
The Collection class performs faster than the native JavaScript Array class for many methods because it does not check for array holes.
Table of contents
- Installation
- Array Holes
- Collection Types
- Usage
- Methods
- all
- at
- btw
- compact
- concat
- every
- exclude
- filter
- find
- findIndex
- first
- flat
- flatMap
- flatSome
- forEach
- forkFlat
- getSize
- getSize
- gt
- gte
- indexOf
- join
- lt
- lte
- map
- mapSome
- match
- matchFlat
- matching
- notMatching
- notNull
- notNullable
- notUndefined
- partition
- pick
- pluck
- precat
- push
- reduce
- reduceRight
- reverse
- skip
- slice
- some
- sort
- take
- tap
- tapSelf
- toArray
- toMap
- toSet
- unique
- unshift
- zip
- zipLong
- Methods
- Publishing a new version
Installation
NPM
npm install @nkp/iterable
Yarn
yarn add @nkp/iterable
Exports
@nkp/iterable targets CommonJS and ES modules. To utilise ES modules consider using a bundler like webpack or rollup.
Array Holes
@nkp/iterable assumes that the iterables fed to them do not have holes.
For consistent behaivour you should not use @nkp/iterable with holey arrays.
Because @nkp/iterable assumes hole-less arrays, the Collection class is faster than the native Array class for a large variety of common operations like filter and map.
Collection types
| type | Collection | LazyCollection |
|---|---|---|
| similar to | array | generator |
| speed | fast | slow |
| memory | heavy | light |
Collection
- speed: fast
- memory: heavy
Collection is similar to the native JavaScript Array class.
Like an array, Collection's values exist in memory at all times.
Collection is memory heavy and very fast. Collection is even faster than the native JavaScript Array class in many situations because it doesn't check for holes.
Collection's methods cause instantaneous transformations of it's internal values, as opposed to LazyCollection which only runs transformations when values are requested.
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3, 4]);
let called = false;
collection // Collection [1, 2, 3, 4]
.map(n => {
called = true;
n + 1;
}) // Collection [2, 3, 4, 5]
.exclude(2) // Collection [3, 4, 5]
.pick(3, 4) // Collection [3, 4]
.sort(-1); // Collection [4, 3]
// transformations have executed upon call
called; // true
collection.toArray(); // Array [4, 3]
LazyCollection
- speed: slow
- memory: light
LazyCollection is a lazy stream that's only calculated when values are requested.
LazyCollection does not store its values in memory, only a reference to the initial iterable provided to it.
LazyCollection stores transformations and doesn't execute them until the caller requests data from it.
import { collectLazy } from '@nkp/iterable';
// generator
function * input(): IterableIterator<number> {
yield 1;
yield 2;
yield 3;
yield 4;
}
const lazy = collectLazy(input);
let called = false;
lazy // LazyCollection [input]
.map(n => {
called = true;
n + 1;
}) // LazyCollection [input]
.exclude(2) // LazyCollection [input]
.pick(3, 4) // LazyCollection [input]
.sort(-1); // LazyCollection [input]
// transformations have not executed yet
called; // false
lazy.toArray(); // Array [4, 3]
// now that data has been requeted, all transformations have run
// and the results have been cached in-case of re-run
called; // true
lazy; // LazyCollection [4, 3]
Internally, values are cached
1. when LazyCollection requires all values in memory for a transformation
2. when the values are requested from the callee
const input = [1, 2, 3];
const lazy = new LazyCollection(input)
.map(n => n + 1)
.exclude(4)
.sort(); // LazyCollection [input]
lazy.toArray(); // all transformations run on [1, 2, 3]
lazy.toArray(); // cached results are returned, transformations do not run again
lazy.at(1); // cached results are returned, transformations do not run again
Usage
Methods
all
Split the collection and operate on it's parts independently then join the results into a tuple (array) and return a single-valued collection with the tuple as it's only value.
Similar to Promise.all, but for collections.
// signature
export interface IHasAll<T> extends Iterable<T> {
all<M extends Record<PropertyKey, Unary<this, unknown>>>(forks: M): IHasAll<{ [K in keyof M]: ReturnType<M[K]> }>;
all<R1>(...splits: readonly [Unary<this, R1>]): IHasAll<[R1]>
all<R1, R2>(...splits: readonly [Unary<this, R1>, Unary<this, R2>]): IHasAll<[R1, R2]>
all<R1, R2, R3>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>]): IHasAll<[R1, R2, R3]>
all<R1, R2, R3, R4>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>]): IHasAll<[R1, R2, R3, R4]>
all<R1, R2, R3, R4, R5>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>]): IHasAll<[R1, R2, R3, R4, R5]>
all<R1, R2, R3, R4, R5, R6>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>]): IHasAll<[R1, R2, R3, R4, R5, R6]>
all<R1, R2, R3, R4, R5, R6, R7>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7]>
all<R1, R2, R3, R4, R5, R6, R7, R8>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9, R10>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>, Unary<this, R10>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9, R10]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>, Unary<this, R10>, Unary<this, R11>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>, Unary<this, R10>, Unary<this, R11>, Unary<this, R12>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>, Unary<this, R10>, Unary<this, R11>, Unary<this, R12>, Unary<this, R13>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>, Unary<this, R10>, Unary<this, R11>, Unary<this, R12>, Unary<this, R13>, Unary<this, R14>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14]>
all<R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15>(...splits: readonly [Unary<this, R1>, Unary<this, R2>, Unary<this, R3>, Unary<this, R4>, Unary<this, R5>, Unary<this, R6>, Unary<this, R7>, Unary<this, R8>, Unary<this, R9>, Unary<this, R10>, Unary<this, R11>, Unary<this, R12>, Unary<this, R13>, Unary<this, R14>, Unary<this, R15>]): IHasAll<[R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15]>
all<R>(...splits: readonly (Unary<this, R>)[]): IHasAll<R[]>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect(['index.html', 'script.js', 'style.css']);
collection
.all(
(html) => html.matching(/\.html$/),
(scripts) => scripts.matching(/\.js$/),
(styles) => styles.matching(/\.css$/),
)
/**
*
* Collection [[
* Collection ['index.html'],
* Collection ['script.js'],
* Collection ['style.css']
* ]]
*/
.first()
/**
* Some [[
* Collection ['index.html'],
* Collection ['script.js'],
* Collection ['style.css']
* ]]
*/
.map(([html, scripts, stypes]) => {
// ...
})
at
Get the value at a specified index.
Providing a negative index searches the collection from back-to-front.
Similar to Array.prototype.at but returns Maybe<T> instead of T.
// signature
import { Maybe } from '@nkp/maybe';
interface IHasAt<T> extends Iterable<T> {
at(index: number): Maybe<T>;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2]).at(0); // Some [1]
collect([1, 2]).at(-1); // Some [-2]
collect([1, 2]).at(2); // None
collect([1, 2]).at(-3); // None
btw
Keep values between the two limits.
// signature
import { Betweenable } from '@nkp/iterable';
interface IHasBtw<T> extends Iterable<T> {
btw(left: Betweenable, right: Betweenable): IHasBtw<T>;
}
// usage
import { collect } from '@nkp/iterable';
// numbers
const numbers = collect([1, 2, 3, 4, 5]);
numbers.btw(2, 4); // Collection [2, 3, 4]
numbers.btw([2, true], 4); // Collection [2, 3, 4]
numbers.btw([2, false], 4); // Collection [ 3, 4]
numbers.btw(2, [4, true]); // Collection [2, 3, 4]
numbers.btw(2, [4, false]); // Collection [2 3 ]
numbers.btw({ value: 2, inclusive: true }, 4); // Collection [2, 3, 4]
numbers.btw({ value: 2, inclusive: false }, 4); // Collection [ 3, 4]
numbers.btw(2, { value: 4, inclusive: true }); // Collection [2, 3, 4]
numbers.btw(2, { value: 4, inclusive: false }); // Collection [2, 3 ]
// dates
const dates = collect([
new Date('1990-01-01'),
new Date('2000-01-01'),
new Date('2010-01-01'),
]);
dates.btw(
new Date('1995-01-01'),
new Date('2005-01-01'),
); // Collection [Date('2000-01-01')]
//
compact
Remove falsy values from the collection.
// signature
interface IHasCompact<T> extends Iterable<T> {
compact(): IHasCompact<NonNullable<T>>;
}
// usage
import { collect } from '@nkp/iterable';
const collection: Collection<number> = collect([1, null, undefined, false, 0, 3]);
collection.notNullable(); // Collection [1, 3]
concat
Concatenate an iterable onto the end of the collection.
Unlike Array.protototype.concat, IHasConcat.concat only accepts a single array argument and does not accept variadic arguments. For spread arguments use push;
// signature
import { Iterateable } from '@nkp/iterable';
interface IHasConcat<T> extends Iterable<T> {
concat(concat: Iterateable<T>): IHasConcat<T>;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2]).concat([3, 4]); // Collection [1, 2, 3, 4]
every
Returns true if the given callback returns truthy for every value in the collection.
Similar to Array.prototype.every and sibling of some.
// signature
interface IHasEvery<T> extends Iterable<T> {
every(callbackfn: ((value: T, currentIndex: number) => boolean)): boolean;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2]).every(Boolean); // true
collect([0, 1]).every(Boolean); // false - 0 is falsy
collect([0, 1]).every(n => n >= 0); // true
exclude
Removes values from the collection that equal any of the given values.
// signature
interface IHasExclude<T> extends Iterable<T> {
exclude(...remove: readonly T[]): IHasExclude<T>;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2, 3]).exclude(1, 2); // Collection [3]
filter
Removes values from the collection if their callback returns falsy.
Similar to Array.prototype.filter.
// signature
interface IHasFilter<T> extends Iterable<T> {
filter<U extends T>(callbackfn: ((value: T, currentIndex: number) => value is U)): IHasFilter<U>;
filter(callbackfn: (value: T, currentIndex: number) => boolean): IHasFilter<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.filter(n => n > 1); // Collection [2, 3]
find
Find a value in the collection.
Similar to Array.prototype.find but returns Maybe<T> instead of T | undefined.
// signature
import { Maybe } from '@nkp/maybe';
interface IHasFind<T> extends Iterable<T> {
find(callbackfn: (value: T, currentIndex: number) => boolean): Maybe<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.find(3); // Some [3]
collection.find(4); // None
findIndex
Find the index of a value in the collection.
Similar to Array.prototype.findIndex but returns Maybe<number> instead of number.
// signature
import { Maybe } from '@nkp/maybe';
interface IHasFindIndex<T> extends Iterable<T> {
findIndex(callbackfn: (value: T, currentIndex: number) => boolean): Maybe<number>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.findIndex(3); // Some [2]
collection.findIndex(4); // None
first
Get the first value from the collection.
Returns Some<T> if the value exists, otherwise returns None.
// signature
import { Maybe } from '@nkp/maybe';
interface IHasFirst<T> extends Iterable<T> {
first(): Maybe<T>;
}
// usage
import { collect } from '@nkp/iterable';
const someCollection = collect([1, 2, 3]);
someCollection.first(); // Some [1]
const noneCollection = collect([]);
noneCollection.first(); // None
flat
Flattens a nested collection where the nested values may by any iterable.
Similar to Array.prototype.flat.
// signature
interface IHasFlat<T> extends Iterable<T> {
flat<U>(this: IHasFlat<Iterable<U>>): IHasFlat<U>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([[1, 2, 3], [4, 5, 6], [7, 8, 9]]);
collection.flat(); // Collection [1, 2, 3, 4, 5, 6, 7, 8, 9]
flatMap
Map the collection's values to iterables and flatten them into single collection.
Similar to Array.prototype.flatMap.
// signature
import { Iterateable } from '@nkp/iterable';
interface IHasFlatMap<T> extends Iterable<T> {
flatMap<U>(callbackfn: (value: T, currentIndex: number) => Iterateable<U>): IHasFlatMap<U>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.map(collect); // Collection [Collection [1], Collection [2], Collection [3]]
collection.flatMap(collect); // Collection [1, 2, 3]
collection.map(collect).flat(); // Collection [1, 2, 3]
flatSome
Flatten Some values and filter out None's from the collection.
The collection must be of type Maybe.
// signature
import { Some, None, Maybe } from '@nkp/iterable';
interface IHasFlatSome<T> extends Iterable<T> {
flatSome<U>(this: IHasFlatSome<Some<U>>): IHasFlatSome<U>;
flatSome<U>(this: IHasFlatSome<Maybe<U>>): IHasFlatSome<U>;
flatSome(this: IHasFlatSome<None>): IHasFlatSome<never>;
}
// usage
import { Maybe } from '@nkp/maybe';
import { collect } from '@nkp/iterable';
const collection = collect([Maybe.some(1), Maybe.none, Maybe.some(3)]);
collection.flatSome(); // Collection [1, 3]
forEach
Execute a callback for each value in the collection.
Similar to Array.prototype.forEach.
// signature
interface IHasForEach<T> extends Iterable<T> {
forEach(callbackfn: ((value: T, index: number) => unknown)): void;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.forEach(n => console.log(n)); // 1, 2, 3
forkFlat
Fork the collection to split and operate on it's parts independently then flatten the results together.
// signature
import { Iterateable } from '@nkp/iterable';
interface IHasForkFlat<T> extends Iterable<T> {
forkFlat<R>(...forks: readonly (Unary<this, Iterateable<R>>)[]): IHasForkFlat<R>;
}
// usage
import { path } from 'path';
import { collect } from '@nkp/iterable';
const collection = collect(['index.html', 'script.js', 'style.css']);
collection.forkFlat(
(html) => html.matching(/\.html$/).map(file => path.join('public', file)),
(scripts) => scripts.matching(/\.js$/).map(file => path.join('public', 'scripts', file)),
(styles) => styles.matching(/\.css$/).map(file => path.join('public', 'styles', file)),
)
// Collection [
// 'public/index.html',
// 'public/scripts/script.js',
// 'public/styles/style.css'
// ]
getSize
Get the size of the collection.
Similar to Array.prototype.length.
// signature
interface IHasGetSize<T> extends Iterable<T> {
getSize(): number;
}
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.getSize(); // 3;
gt
Keep values greater-than the given value.
// signature
import { Orderable } from '@nkp/iterable';
interface IHasGt<T> extends Iterable<T> {
gt(value: Orderable): IHasGt<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.gt(2); // Collection [3]
gte
Keep values greater-than or equal-to the given value.
// signature
import { Orderable } from '@nkp/iterable';
interface IHasGte<T> extends Iterable<T> {
gte(value: Orderable): IHasGte<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.gte(2); // Collection [2, 3]
indexOf
Get the index of the value in the collection.
// signature
import { Maybe } from '@nkp/maybe';
interface IHasIndexOf<T> extends Iterable<T> {
indexOf(value: T): Maybe<number>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.indexOf(2); // Some [1]
collection.indexOf(4); // None
join
Stringify and join collection values with a separator.
Similar to Array.prototype.join.
// signature
interface IHasJoin<T> extends Iterable<T> {
join(separator?: string): string;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect(['hello', 'world']);
collection.join(' '); // 'hello world'
lt
Keep values less-than the given value.
// signature
import { Orderable } from '@nkp/iterable';
interface IHasLt<T> extends Iterable<T> {
lt(value: Orderable): IHasLt<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.lt(2); // Collection [1]
lte
Keep values less-than or equal-to the given value.
// signature
import { Orderable } from '@nkp/iterable';
interface IHasLte<T> extends Iterable<T> {
lte(value: Orderable): IHasLte<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.lte(2); // Collection [1, 2]
map
Map values in the collection.
Similar to Array.prototype.map.
// signature
interface IHasMap<T> extends Iterable<T> {
map<U>(callbackfn: ((value: T, index: number) => U)): IHasMap<U>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.map(n => n + 1); // Collection [1, 2, 3]
mapSelf
Map the collection instance itself.
// signature
interface IHasMapSelf<T> extends Iterable<T> {
mapSelf<U>(callbackfn: ((self: this) => U)): U;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.mapSelf(self => Array.from(self)[0]); // 1
mapSome
Map into a Maybe and filter and flatten the value back into a collection.
// signature
import { Maybe, } from '@nkp/iterable';
interface IHasMapSome<T> extends Iterable<T> {
mapSome<U>(callbackfn: (value: T, currentIndex: number) => Maybe<U>): IHasMapSome<U>;
}
// usage
import { Maybe } from '@nkp/maybe';
import { collect } from '@nkp/iterable';
const collection = collect([1, 3]);
collection.mapSome(
(n) => n <= 1 ? Maybe.some(n) : Maybe.none);
// Collection [1]
match
Match items against the regex.
Returns Some if the match succeded and None if not.
// signature
import { Maybe } from '@nkp-maybe';
interface IHasMatch<T> extends IHasForEach<T> {
match(regexp: string | RegExp): IHasMatch<Maybe<RegExpMatchArray>>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect(['index.html', 'style.css', 'script.js']);
collection.match(/\.(css|js)$/);
/**
* Collection [
* None
* Some [[RegExpMatchArray] {
* 0: '.css',
* 1: 'css',
* index: 5,
* input: 'style.css',
* groups: undefined,
* }]
* Some [[RegExpMatchArray] {
* 0: '.js',
* 1: 'js',
* index: 5,
* input: 'style.css',
* groups: undefined,
* }]
* ]
*/
matchFlat
Match items against the regex.
Only keeps successful matches.
// signature
interface IHasMatchFlat<T> extends Iterable<T> {
matchFlat(regexp: string | RegExp): IHasMatch<RegExpMatchArray>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect(['index.html', 'style.css', 'script.js']);
collection.matchFlat(/\.(css|js)$/);
/**
* Collection [
* [RegExpMatchArray] {
* 0: '.css',
* 1: 'css',
* index: 5,
* input: 'style.css',
* groups: undefined,
* }
* [RegExpMatchArray] {
* 0: '.js',
* 1: 'js',
* index: 5,
* input: 'style.css',
* groups: undefined,
* }
* ]
*/
matching
Keeps values matching the given regex.
// signature
interface IHasMatching<T> extends IHasForEach<T> {
matching(regexp: RegExp | string): IHasMatching<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect(['index.html', 'style.css', 'script.js']);
collection.matching(/\.css$/); // Collection ['style.css']
notMatching
Removes values matching the given regex from the collection.
// signature
interface IHasNotMatching<T> extends Iterable<T> {
notMatching(regexp: RegExp | string): IHasNotMatching<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect(['index.html', 'style.css', 'script.js']);
collection.notMatching(/\.css$/); // Collection ['index.html', 'script.js']
notNull
Remove null values from the collection.
// signature
interface IHasNotNull<T> extends Iterable<T> {
notNull(): IHasNotNull<T extends null ? never : T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, null, 3]);
collection.notNull(); // Collection [1, 3]
notNullable
Remove null and undefined values from the collection.
// signature
interface IHasNotNullable<T> extends Iterable<T> {
notNullable(): IHasNotNullable<NonNullable<T>>;
}
// usage
import { collect } from '@nkp/iterable';
const collection: Collection<number> = collect([1, null, undefined, 3]);
collection.notNullable(); // Collection [1, 3]
notUndefined
Removes undefined values from the collection.
// signature
interface IHasNotUndefined<T> extends Iterable<T> {
notUndefined(): IHasNotUndefined<T extends undefined ? never : T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, undefined, 3]);
collection.notUndefined(); // Collection [1, 3]
partition
Partition the collection grouping by callback return value
// signature
interface IHasPartition<T> extends Iterable<T> {
partition<R>(callbackfn: ((
value: T,
index: number
) => R)): IHasPartition<IHasPartition<T>>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([
'contact/index.html',
'contact/script.js',
'contact/style.css',
'about/index.html',
'about/script.js',
'about/style.css',
]);
collection
.partition(
// fork on the directory name
(html) => html.match(/(.*)[\\/][^\\/\.]*\.html$/).first().value,
(scripts) => scripts.match(/(.*)[\\/][^\\/\.]*\.js$/).first().value,
(styles) => styles.match(/(.*)[\\/][^\\/\.]*\.css$/).first().value,
)
/**
*
* Collection [
* Collection [
* 'contact/index.html'
* 'contact/script.js'
* 'contact/style.css'
* ],
* Collection [
* 'about/index.html'
* 'about/script.js'
* 'about/style.css'
* ],
* ]
*/
pick
Keep values in the collection that equal any of the given values.
// signature
interface IHasPick<T> extends Iterable<T> {
pick(...keep: readonly T[]): IHasPick<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.pick(1, 2); // Collection [1, 2]
pluck
Pluck the key from each value in the collection.
// signature
interface IHasPluck<T> extends IHasForEach<T> {
pluck<K extends keyof T>(key: K): IHasPluck<T[K]>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collection([
{ prop: 'a' },
{ prop: 'b' },
{ prop: 'c' },
]);
collection.pluck('prop'); // Collection ['a', 'b', 'c']
precat
Concatenate an iterable onto the start of the collection.
// signature
import { Iterateable } from '@nkp/iterable';
interface IHasPrecat<T> extends Iterable<T> {
precat(precat: Iterateable<T>): IHasPrecat<T>;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2]).precat([3, 4]); // Collection [3, 4, 1, 2]
push
Push values onto the end of the collection.
Similar to Array.prototype.push but returns the new collection instead of the number of arguments pushed.
// signature
interface IHasPush<T> extends Iterable<T> {
push(...pushed: T[]): IHasPush<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.push(4, 5); // Collection [1, 2, 3, 4, 5]
reduce
Reduce the collection to a single value.
Similar to Array.prototype.reduce.
// signature
interface IHasReduce<T> extends Iterable<T> {
reduce<U>(
callbackfn: ((
previousValue: T,
currentValue: U,
currentIndex: number
) => U),
initial: U,
): U;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
// sum the collection from left-to-right
collection.reduce((next, acc) => acc + next, 0); // 6
reduceRight
Reduce the collection to a single value, from right to left.
Similar to Array.prototype.reduceRight.
// signature
interface IHasReduceRight<T> extends Iterable<T> {
reduceRight<U>(
callbackfn: ((
previousValue: T,
currentValue: U,
currentIndex: number
) => U),
initial: U,
): U;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
// stringify and concatenate the collection values from right-to-left
collection.reduceRight((next, acc) => acc + String(next), ''); // '321'
reverse
Reverse the ordering of values in the collection.
Similar to Array.prototype.reverse but does not mutate the callee.
// signature
interface IHasReverse<T> extends Iterable<T> {
reverse(): IHasReverse<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.reverse(); // Collection [3, 2, 1]
// not mutated
collection; // Collection [1, 2, 3]
skip
Removes the first n values from the collection.
// signature
interface IHasSkip<T> extends Iterable<T> {
skip(count?: number): IHasSkip<T>;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2, 3]).skip(2); // Collection [3]
slice
Slice elements from the collection from start to end.
Similar to Array.prototype.slice.
// signature
interface IHasSlice<T> extends Iterable<T> {
slice(start?: number, end?: number): IHasSlice<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([0, 1, 2, 3, 4]);
// from index 2, ending before index 4
collection.slice(2, 4); // Collection [2, 3]
some
Returns true if the callback returns truthy for any value in the collection.
Similar to Array.prototype.some. Sibling of every.
// signature
interface IHasSome<T> extends Iterable<T> {
some(callbackfn: (value: T, currentIndex: number) => boolean): boolean;
}
// usage
import { collect } from '@nkp/iterable';
collect([1, 2]).some(Boolean); // true
collect([0, 1]).some(Boolean); // true
collect([0, 0]).some(Boolean); // false
collect([0, false]).some(Boolean); // false
sort
Sorts values in the collection with sensible defaults.
Similar to Array.prototype.sort but sorts numerically by default instead of alphabetically and does not mutate the callee.
// signature
import { SortDirection } from '@nkp/sort';
interface IHasSort<T> extends Iterable<T> {
sort(sort: SortDirection<T>): IHasSort<T>;
}
/**
* type SortDirection<T> =
* | 'asc' | 'ASC'
* | 'desc' | 'DESC'
* | 1 | '1'
* | -1 | '-1'
* | ((a: T, b: T) => number)
*/
// usage
import { collect } from '@nkp/iterable';
// numeric only
const numeric = collect([1, 4, BigInt(3), 2]);
// ascending
numeric.sort(1); // Collection [1, 2, BigInt(3), 4]
// descending
numeric.sort(-1); // Collection [4, BigInt(3), 2, 1]
// alphabetical only - sorts by char code
const alpha = collect(['a', 'c', 'B', 'd']);
// ascending
alpha.sort(1); // Collection ['B', 'a', 'c', 'd']
// descending
alpha.sort(-1); // Collection ['d', 'c', 'a', 'B']
// alphabetic and numeric
// sorts numerically then alphabetically
const alpha = collect([1, 'a', 3, 'c', 2, 'b']);
// ascending
alpha.sort(1); // Collection [1, 2, 3, 'a', 'b', 'c']
// desecending
alpha.sort(-1); // Collection ['c', 'b', 'a', 3, 2, 1]
take
Keep the first n values in the collection.
// signature
interface IHasTake<T> extends Iterable<T> {
take(count?: number): IHasTake<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.take(2); // Collection [1, 2]
tap
Execute a callback for each value in the collection without changing the collection.
Useful for logging.
Similar to Array.prototype.forEach but returns the collection.
// signature
interface IHasTap<T> extends Iterable<T> {
tap(callbackfn: ((value: T, index: number) => unknown)): this;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection
.tap((value, i) => console.log(`${i}: ${value}`));
// 0: 1
// 1: 2
// 2: 3
.map((value) => {
// ...
});
tapSelf
Execute a callback with a reference to the collection itself.
Returns the original collection.
Useful for logging.
// signature
interface IHasTapSelf<T> extends Iterable<T> {
tapSelf(callbackfn: ((self: IHasTapSelf<T>) => unknown)): this;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection
.map((value) => value + 1)
.tapSelf((c) => console.log(`Right now the collection is: ${c.toString()}`))
.map((value) => {
// ...
});
toArray
Transform the collection into n array.
// signature
interface IHasToArray<T> extends Iterable<T> {
toArray(): Array<T>
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.toArray(); // Array [1, 2, 3]
toSet
Transform the collection into an ES6 set.
// signature
interface IHasToSet<T> extends Iterable<T> {
toSet(): Set<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3, 3]);
collection.toSet(); // Set [1, 2, 3]
toMap
Transform the collection into an ES6 map.
// signature
interface IHasToMap<T> extends Iterable<T> {
toMap<K, V>(this: IHasToMap<[K, V]>): Map<K, V>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect<[number, number]>([[1, 1], [2, 2], [3, 3]]);
collection.toMap(); // Map [[1, 1], [2, 2], [3, 3]]
unique
Remove duplicate values from the collection.
// signature
interface IHasUnique<T> extends Iterable<T> {
unique(): IHasUnique<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 2]);
collection.unique(); // Collection [1, 2]
unshift
Shift values onto the front of the collection.
Similar to Array.prototype.shift.
// signature
interface IHasUnshift<T> extends Iterable<T> {
unshift(...unshifted: readonly T[]): IHasUnshift<T>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.shift(-1, -2, -3); // Collection [-1, -2, -3, 1, 2, 3]
zip
Join the collection with an iterable, by index.
The resulting collection terminates with the first input iterable.
// signature
import { Iterateable } from '@nkp/iterable';
interface IHasZip<T> extends Iterable<T> {
zip<U>(right: Iterateable<U>): IHasZipShort<[T, U]>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.zip([-1, -2, -3, -4]);
// Collection<[
// [1, -1,],
// [2, -2,],
// [3, -3,],
// ]>
zipLong
Join the collection with an iterable, by index.
The resulting collection terminates with the final input iterable.
// signature
import { Iterateable } from '@nkp/iterateable';
import { Maybe } from '@nkp/maybe';
interface IHasZipLong<T> extends Iterable<T> {
zipLong<U>(right: Iterateable<U>): IHasZipLong<[Maybe<T>, Maybe<U>]>;
}
// usage
import { collect } from '@nkp/iterable';
const collection = collect([1, 2, 3]);
collection.zipLong([-1, -2, -3, -4]);
// Collection<[
// [Some<1>, Some<-1>,],
// [Some<2>, Some<-2>,],
// [Some<3>, Some<-3>,],
// [None, Some<-4>,],
// ]>
Publishing a new version
To a release a new version:
- Update the version number in package.json
- Push the new version to the
masterbranch on GitHub - Create a
new releaseon GitHub for the latest version
This will trigger a GitHub action that tests and publishes the npm package.
1.0.0 - 2021-09-08
Launched stable version v1.0.0
Changed
- Updated dependencies
Keywords
FAQs
Iteration utility for synchronous iterators like arrays, sets, maps and generators.
We found that @nkp/iterable demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
Package last updated on 09 Sep 2021
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