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I highly recommend reading this: So, what's next?

Modular standard library for JavaScript. Includes polyfills for ECMAScript up to 2024: promises, symbols, collections, iterators, typed arrays, many other features, ECMAScript proposals, some cross-platform WHATWG / W3C features and proposals like URL. You can load only required features or use it without global namespace pollution.

If you are looking for documentation for obsolete core-js@2, please, check this branch.

core-js@3, babel and a look into the future

Raising funds

core-js isn't backed by a company, so the future of this project depends on you. Become a sponsor or a backer if you are interested in core-js: Open Collective, Patreon, Boosty, Bitcoin ( bc1qlea7544qtsmj2rayg0lthvza9fau63ux0fstcz ), Alipay.


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Example of usage:

import 'core-js/actual';

Promise.resolve(42).then(it => console.log(it)); // => 42

Array.from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]

[1, 2].flatMap(it => [it, it]); // => [1, 1, 2, 2]

(function * (i) { while (true) yield i++; })(1)
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])

You can load only required features:

import 'core-js/actual/promise';
import 'core-js/actual/set';
import 'core-js/actual/iterator';
import 'core-js/actual/array/from';
import 'core-js/actual/array/flat-map';
import 'core-js/actual/structured-clone';

Promise.resolve(42).then(it => console.log(it)); // => 42

Array.from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]

[1, 2].flatMap(it => [it, it]); // => [1, 1, 2, 2]

(function * (i) { while (true) yield i++; })(1)
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])

Or use it without global namespace pollution:

import Promise from 'core-js-pure/actual/promise';
import Set from 'core-js-pure/actual/set';
import Iterator from 'core-js-pure/actual/iterator';
import from from 'core-js-pure/actual/array/from';
import flatMap from 'core-js-pure/actual/array/flat-map';
import structuredClone from 'core-js-pure/actual/structured-clone';

Promise.resolve(42).then(it => console.log(it)); // => 42

from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]

flatMap([1, 2], it => [it, it]); // => [1, 1, 2, 2]

Iterator.from(function * (i) { while (true) yield i++; }(1))
  .drop(1).take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])

Index

Usage

Installation:

// global version
npm install --save core-js@3.39.0
// version without global namespace pollution
npm install --save core-js-pure@3.39.0
// bundled global version
npm install --save core-js-bundle@3.39.0

Or you can use core-js from CDN.

postinstall message

The core-js project needs your help, so the package shows a message about it after installation. If it causes problems for you, you can disable it:

ADBLOCK=true npm install
// or
DISABLE_OPENCOLLECTIVE=true npm install
// or
npm install --loglevel silent

CommonJS API

You can import only-required-for-you polyfills, like in the examples at the top of README.md. Available CommonJS entry points for all polyfilled methods / constructors and namespaces. Just some examples:

// polyfill all `core-js` features, including early-stage proposals:
import "core-js";
// or:
import "core-js/full";
// polyfill all actual features - stable ES, web standards and stage 3 ES proposals:
import "core-js/actual";
// polyfill only stable features - ES and web standards:
import "core-js/stable";
// polyfill only stable ES features:
import "core-js/es";

// if you want to polyfill `Set`:
// all `Set`-related features, with early-stage ES proposals:
import "core-js/full/set";
// stable required for `Set` ES features, features from web standards and stage 3 ES proposals:
import "core-js/actual/set";
// stable required for `Set` ES features and features from web standards
// (DOM collections iterator in this case):
import "core-js/stable/set";
// only stable ES features required for `Set`:
import "core-js/es/set";
// the same without global namespace pollution:
import Set from "core-js-pure/full/set";
import Set from "core-js-pure/actual/set";
import Set from "core-js-pure/stable/set";
import Set from "core-js-pure/es/set";

// if you want to polyfill just the required methods:
import "core-js/full/set/intersection";
import "core-js/actual/array/find-last";
import "core-js/stable/queue-microtask";
import "core-js/es/array/from";

// polyfill iterator helpers proposal:
import "core-js/proposals/iterator-helpers";
// polyfill all stage 2+ proposals:
import "core-js/stage/2";

[!TIP] The usage of the /actual/ namespace is recommended since it includes all actual JavaScript features and does not include unstable early-stage proposals that are available mainly for experiments.

[!WARNING]

CommonJS and prototype methods without global namespace pollution

In the pure version, we can't pollute prototypes of native constructors. Because of that, prototype methods transformed into static methods like in examples above. But with transpilers, we can use one more trick - bind operator and virtual methods. Special for that, available /virtual/ entry points. Example:

import fill from 'core-js-pure/actual/array/virtual/fill';
import findIndex from 'core-js-pure/actual/array/virtual/find-index';

Array(10)::fill(0).map((a, b) => b * b)::findIndex(it => it && !(it % 8)); // => 4

[!WARNING] The bind operator is an early-stage ECMAScript proposal and usage of this syntax can be dangerous.

Babel

core-js is integrated with babel and is the base for polyfilling-related babel features:

@babel/polyfill

@babel/polyfill IS just the import of stable core-js features and regenerator-runtime for generators and async functions, so if you load @babel/polyfill - you load the global version of core-js without ES proposals.

Now it's deprecated in favor of separate inclusion of required parts of core-js and regenerator-runtime and, for preventing breaking changes, left on core-js@2.

As a full equal of @babel/polyfill, you can use this:

import 'core-js/stable';
import 'regenerator-runtime/runtime';

@babel/preset-env

@babel/preset-env has useBuiltIns option, which optimizes working with the global version of core-js. With useBuiltIns option, you should also set corejs option to the used version of core-js, like corejs: '3.39'.

[!IMPORTANT] Recommended to specify used minor core-js version, like corejs: '3.39', instead of corejs: 3, since with corejs: 3 will not be injected modules which were added in minor core-js releases.


import 'core-js/stable';

with chrome 71 target will be replaced just to:

import 'core-js/modules/es.array.unscopables.flat';
import 'core-js/modules/es.array.unscopables.flat-map';
import 'core-js/modules/es.object.from-entries';
import 'core-js/modules/web.immediate';

It works for all entry points of global version of core-js and their combinations, for example for

import 'core-js/es';
import 'core-js/proposals/set-methods';
import 'core-js/full/set/map';

with chrome 71 target you will have as the result:

import 'core-js/modules/es.array.unscopables.flat';
import 'core-js/modules/es.array.unscopables.flat-map';
import 'core-js/modules/es.object.from-entries';
import 'core-js/modules/esnext.set.difference';
import 'core-js/modules/esnext.set.intersection';
import 'core-js/modules/esnext.set.is-disjoint-from';
import 'core-js/modules/esnext.set.is-subset-of';
import 'core-js/modules/esnext.set.is-superset-of';
import 'core-js/modules/esnext.set.map';
import 'core-js/modules/esnext.set.symmetric-difference';
import 'core-js/modules/esnext.set.union';
// first file:
let set = new Set([1, 2, 3]);
// second file:
let array = Array.of(1, 2, 3);

if the target contains an old environment like IE 11 we will have something like:

// first file:
import 'core-js/modules/es.array.iterator';
import 'core-js/modules/es.object.to-string';
import 'core-js/modules/es.set';

var set = new Set([1, 2, 3]);
// second file:
import 'core-js/modules/es.array.of';

var array = Array.of(1, 2, 3);

By default, @babel/preset-env with useBuiltIns: 'usage' option only polyfills stable features, but you can enable polyfilling of proposals by the proposals option, as corejs: { version: '3.39', proposals: true }.

[!IMPORTANT] In the case of useBuiltIns: 'usage', you should not add core-js imports by yourself, they will be added automatically.

@babel/runtime

@babel/runtime with corejs: 3 option simplifies work with the core-js-pure. It automatically replaces the usage of modern features from the JS standard library to imports from the version of core-js without global namespace pollution, so instead of:

import from from 'core-js-pure/stable/array/from';
import flat from 'core-js-pure/stable/array/flat';
import Set from 'core-js-pure/stable/set';
import Promise from 'core-js-pure/stable/promise';

from(new Set([1, 2, 3, 2, 1]));
flat([1, [2, 3], [4, [5]]], 2);
Promise.resolve(32).then(x => console.log(x));

you can write just:

Array.from(new Set([1, 2, 3, 2, 1]));
[1, [2, 3], [4, [5]]].flat(2);
Promise.resolve(32).then(x => console.log(x));

By default, @babel/runtime only polyfills stable features, but like in @babel/preset-env, you can enable polyfilling of proposals by proposals option, as corejs: { version: 3, proposals: true }.

[!WARNING] If you use @babel/preset-env and @babel/runtime together, use corejs option only in one place since it's duplicate functionality and will cause conflicts.

swc

Fast JavaScript transpiler swc contains integration with core-js, that optimizes work with the global version of core-js. Like @babel/preset-env, it has 2 modes: usage and entry, but usage mode still works not so well as in babel. Example of configuration in .swcrc:

{
  "env": {
    "targets": "> 0.25%, not dead",
    "mode": "entry",
    "coreJs": "3.39"
  }
}

Configurable level of aggressiveness

By default, core-js sets polyfills only when they are required. That means that core-js checks if a feature is available and works correctly or not and if it has no problems, core-js uses native implementation.

But sometimes core-js feature detection could be too strict for your case. For example, Promise constructor requires the support of unhandled rejection tracking and @@species.

Sometimes we could have an inverse problem - a knowingly broken environment with problems not covered by core-js feature detection.

For those cases, we could redefine this behavior for certain polyfills:

const configurator = require('core-js/configurator');

configurator({
  useNative: ['Promise'],                                 // polyfills will be used only if natives are completely unavailable
  usePolyfill: ['Array.from', 'String.prototype.padEnd'], // polyfills will be used anyway
  useFeatureDetection: ['Map', 'Set'],                    // default behavior
});

require('core-js/actual');

It does not work with some features. Also, if you change the default behavior, even core-js internals may not work correctly.

Custom build

For some cases could be useful to exclude some core-js features or generate a polyfill for target engines. You could use core-js-builder package for that.

Supported engines and compatibility data

core-js tries to support all possible JS engines and environments with ES3 support. Some features have a higher lower bar - for example, some accessors can properly work only from ES5, promises require a way to set a microtask or a task, etc.

However, I have no possibility to test core-js absolutely everywhere - for example, testing in IE7- and some other ancient was stopped. The list of definitely supported engines you can see in the compatibility table by the link below. Write if you have issues or questions with the support of any engine.

core-js project provides (as core-js-compat package) all required data about the necessity of core-js modules, entry points, and tools for work with it - it's useful for integration with tools like babel or swc. If you wanna help, you could take a look at the related section of CONTRIBUTING.md. The visualization of compatibility data and the browser tests runner is available here, the example:

compat-table

Features:

CommonJS entry points:

core-js(-pure)

ECMAScript

CommonJS entry points:

core-js(-pure)/es

ECMAScript: Object

Modules es.object.assign, es.object.create, es.object.define-getter, es.object.define-property, es.object.define-properties, es.object.define-setter, es.object.entries, es.object.freeze, es.object.from-entries, es.object.get-own-property-descriptor, es.object.get-own-property-descriptors, es.object.get-own-property-names, es.object.get-prototype-of, es.object.group-by, es.object.has-own, es.object.is, es.object.is-extensible, es.object.is-frozen, es.object.is-sealed, es.object.keys, es.object.lookup-setter, es.object.lookup-getter, es.object.prevent-extensions, es.object.proto, es.object.to-string, es.object.seal, es.object.set-prototype-of, es.object.values.

class Object {
  toString(): string; // ES2015+ fix: @@toStringTag support
  __defineGetter__(property: PropertyKey, getter: Function): void;
  __defineSetter__(property: PropertyKey, setter: Function): void;
  __lookupGetter__(property: PropertyKey): Function | void;
  __lookupSetter__(property: PropertyKey): Function | void;
  __proto__: Object | null; // required a way setting of prototype - will not in IE10-, it's for modern engines like Deno
  static assign(target: Object, ...sources: Array<Object>): Object;
  static create(prototype: Object | null, properties?: { [property: PropertyKey]: PropertyDescriptor }): Object;
  static defineProperties(object: Object, properties: { [property: PropertyKey]: PropertyDescriptor })): Object;
  static defineProperty(object: Object, property: PropertyKey, attributes: PropertyDescriptor): Object;
  static entries(object: Object): Array<[string, mixed]>;
  static freeze(object: any): any;
  static fromEntries(iterable: Iterable<[key, value]>): Object;
  static getOwnPropertyDescriptor(object: any, property: PropertyKey): PropertyDescriptor | void;
  static getOwnPropertyDescriptors(object: any): { [property: PropertyKey]: PropertyDescriptor };
  static getOwnPropertyNames(object: any): Array<string>;
  static getPrototypeOf(object: any): Object | null;
  static groupBy(items: Iterable, callbackfn: (value: any, index: number) => key): { [key]: Array<mixed> };
  static hasOwn(object: object, key: PropertyKey): boolean;
  static is(value1: any, value2: any): boolean;
  static isExtensible(object: any): boolean;
  static isFrozen(object: any): boolean;
  static isSealed(object: any): boolean;
  static keys(object: any): Array<string>;
  static preventExtensions(object: any): any;
  static seal(object: any): any;
  static setPrototypeOf(target: any, prototype: Object | null): any; // required __proto__ - IE11+
  static values(object: any): Array<mixed>;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/object
core-js(-pure)/es|stable|actual|full/object/assign
core-js(-pure)/es|stable|actual|full/object/is
core-js(-pure)/es|stable|actual|full/object/set-prototype-of
core-js(-pure)/es|stable|actual|full/object/get-prototype-of
core-js(-pure)/es|stable|actual|full/object/create
core-js(-pure)/es|stable|actual|full/object/define-property
core-js(-pure)/es|stable|actual|full/object/define-properties
core-js(-pure)/es|stable|actual|full/object/get-own-property-descriptor
core-js(-pure)/es|stable|actual|full/object/get-own-property-descriptors
core-js(-pure)/es|stable|actual|full/object/group-by
core-js(-pure)/es|stable|actual|full/object/has-own
core-js(-pure)/es|stable|actual|full/object/keys
core-js(-pure)/es|stable|actual|full/object/values
core-js(-pure)/es|stable|actual|full/object/entries
core-js(-pure)/es|stable|actual|full/object/get-own-property-names
core-js(-pure)/es|stable|actual|full/object/freeze
core-js(-pure)/es|stable|actual|full/object/from-entries
core-js(-pure)/es|stable|actual|full/object/seal
core-js(-pure)/es|stable|actual|full/object/prevent-extensions
core-js/es|stable|actual|full/object/proto
core-js(-pure)/es|stable|actual|full/object/is-frozen
core-js(-pure)/es|stable|actual|full/object/is-sealed
core-js(-pure)/es|stable|actual|full/object/is-extensible
core-js/es|stable|actual|full/object/to-string
core-js(-pure)/es|stable|actual|full/object/define-getter
core-js(-pure)/es|stable|actual|full/object/define-setter
core-js(-pure)/es|stable|actual|full/object/lookup-getter
core-js(-pure)/es|stable|actual|full/object/lookup-setter

Examples:

let foo = { q: 1, w: 2 };
let bar = { e: 3, r: 4 };
let baz = { t: 5, y: 6 };
Object.assign(foo, bar, baz); // => foo = { q: 1, w: 2, e: 3, r: 4, t: 5, y: 6 }

Object.is(NaN, NaN); // => true
Object.is(0, -0);    // => false
Object.is(42, 42);   // => true
Object.is(42, '42'); // => false

function Parent() { /* empty */ }
function Child() { /* empty */ }
Object.setPrototypeOf(Child.prototype, Parent.prototype);
new Child() instanceof Child;  // => true
new Child() instanceof Parent; // => true

({
  [Symbol.toStringTag]: 'Foo',
}).toString(); // => '[object Foo]'

Object.keys('qwe'); // => ['0', '1', '2']
Object.getPrototypeOf('qwe') === String.prototype; // => true

Object.values({ a: 1, b: 2, c: 3 });  // => [1, 2, 3]
Object.entries({ a: 1, b: 2, c: 3 }); // => [['a', 1], ['b', 2], ['c', 3]]

for (let [key, value] of Object.entries({ a: 1, b: 2, c: 3 })) {
  console.log(key);   // => 'a', 'b', 'c'
  console.log(value); // => 1, 2, 3
}

// Shallow object cloning with prototype and descriptors:
let copy = Object.create(Object.getPrototypeOf(object), Object.getOwnPropertyDescriptors(object));
// Mixin:
Object.defineProperties(target, Object.getOwnPropertyDescriptors(source));

const map = new Map([['a', 1], ['b', 2]]);
Object.fromEntries(map); // => { a: 1, b: 2 }

class Unit {
  constructor(id) {
    this.id = id;
  }
  toString() {
    return `unit${ this.id }`;
  }
}

const units = new Set([new Unit(101), new Unit(102)]);

Object.fromEntries(units.entries()); // => { unit101: Unit { id: 101 }, unit102: Unit { id: 102 } }

Object.hasOwn({ foo: 42 }, 'foo'); // => true
Object.hasOwn({ foo: 42 }, 'bar'); // => false
Object.hasOwn({}, 'toString');     // => false

Object.groupBy([1, 2, 3, 4, 5], it => it % 2); // => { 1: [1, 3, 5], 0: [2, 4] }

ECMAScript: Function

Modules es.function.name, es.function.has-instance. Just ES5: es.function.bind.

class Function {
  name: string;
  bind(thisArg: any, ...args: Array<mixed>): Function;
  @@hasInstance(value: any): boolean;
}

CommonJS entry points:

core-js/es|stable|actual|full/function
core-js/es|stable|actual|full/function/name
core-js/es|stable|actual|full/function/has-instance
core-js(-pure)/es|stable|actual|full/function/bind
core-js(-pure)/es|stable|actual|full/function/virtual/bind

Example:

(function foo() { /* empty */ }).name; // => 'foo'

console.log.bind(console, 42)(43); // => 42 43

ECMAScript: Error

Modules es.aggregate-error, es.aggregate-error.cause, es.error.cause, es.error.to-string.

class [
  Error,
  EvalError,
  RangeError,
  ReferenceError,
  SyntaxError,
  TypeError,
  URIError,
  WebAssembly.CompileError,
  WebAssembly.LinkError,
  WebAssembly.RuntimeError,
] {
  constructor(message: string, { cause: any }): %Error%;
}

class AggregateError extends Error {
  constructor(errors: Iterable, message?: string, { cause: any }?): AggregateError;
  errors: Array<any>;
  message: string;
  cause: any;
}

class Error {
  toString(): string; // different fixes
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/aggregate-error
core-js/es|stable|actual|full/error
core-js/es|stable|actual|full/error/constructor
core-js/es|stable|actual|full/error/to-string

Example:

const error1 = new TypeError('Error 1');
const error2 = new TypeError('Error 2');
const aggregate = new AggregateError([error1, error2], 'Collected errors');
aggregate.errors[0] === error1; // => true
aggregate.errors[1] === error2; // => true

const cause = new TypeError('Something wrong');
const error = new TypeError('Here explained what`s wrong', { cause });
error.cause === cause; // => true

Error.prototype.toString.call({ message: 1, name: 2 }) === '2: 1'; // => true

ECMAScript: Array

Modules es.array.from, es.array.is-array, es.array.of, es.array.copy-within, es.array.fill, es.array.find, es.array.find-index, es.array.find-last, es.array.find-last-index, es.array.iterator, es.array.includes, es.array.push, es.array.slice, es.array.join, es.array.unshift, es.array.index-of, es.array.last-index-of, es.array.every, es.array.some, es.array.for-each, es.array.map, es.array.filter, es.array.reduce, es.array.reduce-right, es.array.reverse, es.array.sort, es.array.flat, es.array.flat-map, es.array.unscopables.flat, es.array.unscopables.flat-map, es.array.at, es.array.to-reversed, es.array.to-sorted, es.array.to-spliced, es.array.with.

class Array {
  at(index: int): any;
  concat(...args: Array<mixed>): Array<mixed>; // with adding support of @@isConcatSpreadable and @@species
  copyWithin(target: number, start: number, end?: number): this;
  entries(): Iterator<[index, value]>;
  every(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): boolean;
  fill(value: any, start?: number, end?: number): this;
  filter(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): Array<mixed>; // with adding support of @@species
  find(callbackfn: (value: any, index: number, target: any) => boolean), thisArg?: any): any;
  findIndex(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): uint;
  findLast(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): any;
  findLastIndex(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): uint;
  flat(depthArg?: number = 1): Array<mixed>;
  flatMap(mapFn: (value: any, index: number, target: any) => any, thisArg: any): Array<mixed>;
  forEach(callbackfn: (value: any, index: number, target: any) => void, thisArg?: any): void;
  includes(searchElement: any, from?: number): boolean;
  indexOf(searchElement: any, from?: number): number;
  join(separator: string = ','): string;
  keys(): Iterator<index>;
  lastIndexOf(searchElement: any, from?: number): number;
  map(mapFn: (value: any, index: number, target: any) => any, thisArg?: any): Array<mixed>; // with adding support of @@species
  push(...args: Array<mixed>): uint;
  reduce(callbackfn: (memo: any, value: any, index: number, target: any) => any, initialValue?: any): any;
  reduceRight(callbackfn: (memo: any, value: any, index: number, target: any) => any, initialValue?: any): any;
  reverse(): this; // Safari 12.0 bug fix
  slice(start?: number, end?: number): Array<mixed>; // with adding support of @@species
  splice(start?: number, deleteCount?: number, ...items: Array<mixed>): Array<mixed>; // with adding support of @@species
  some(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): boolean;
  sort(comparefn?: (a: any, b: any) => number): this; // with modern behavior like stable sort
  toReversed(): Array<mixed>;
  toSpliced(start?: number, deleteCount?: number, ...items: Array<mixed>): Array<mixed>;
  toSorted(comparefn?: (a: any, b: any) => number): Array<mixed>;
  unshift(...args: Array<mixed>): uint;
  values(): Iterator<value>;
  with(index: includes, value: any): Array<mixed>;
  @@iterator(): Iterator<value>;
  @@unscopables: { [newMethodNames: string]: true };
  static from(items: Iterable | ArrayLike, mapFn?: (value: any, index: number) => any, thisArg?: any): Array<mixed>;
  static isArray(value: any): boolean;
  static of(...args: Array<mixed>): Array<mixed>;
}

class Arguments {
  @@iterator(): Iterator<value>; // available only in core-js methods
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/array
core-js(-pure)/es|stable|actual|full/array/from
core-js(-pure)/es|stable|actual|full/array/of
core-js(-pure)/es|stable|actual|full/array/is-array
core-js(-pure)/es|stable|actual|full/array(/virtual)/at
core-js(-pure)/es|stable|actual|full/array(/virtual)/concat
core-js(-pure)/es|stable|actual|full/array(/virtual)/copy-within
core-js(-pure)/es|stable|actual|full/array(/virtual)/entries
core-js(-pure)/es|stable|actual|full/array(/virtual)/every
core-js(-pure)/es|stable|actual|full/array(/virtual)/fill
core-js(-pure)/es|stable|actual|full/array(/virtual)/filter
core-js(-pure)/es|stable|actual|full/array(/virtual)/find
core-js(-pure)/es|stable|actual|full/array(/virtual)/find-index
core-js(-pure)/es|stable|actual|full/array(/virtual)/find-last
core-js(-pure)/es|stable|actual|full/array(/virtual)/find-last-index
core-js(-pure)/es|stable|actual|full/array(/virtual)/flat
core-js(-pure)/es|stable|actual|full/array(/virtual)/flat-map
core-js(-pure)/es|stable|actual|full/array(/virtual)/for-each
core-js(-pure)/es|stable|actual|full/array(/virtual)/includes
core-js(-pure)/es|stable|actual|full/array(/virtual)/index-of
core-js(-pure)/es|stable|actual|full/array(/virtual)/iterator
core-js(-pure)/es|stable|actual|full/array(/virtual)/join
core-js(-pure)/es|stable|actual|full/array(/virtual)/keys
core-js(-pure)/es|stable|actual|full/array(/virtual)/last-index-of
core-js(-pure)/es|stable|actual|full/array(/virtual)/map
core-js(-pure)/es|stable|actual|full/array(/virtual)/push
core-js(-pure)/es|stable|actual|full/array(/virtual)/reduce
core-js(-pure)/es|stable|actual|full/array(/virtual)/reduce-right
core-js(-pure)/es|stable|actual|full/array(/virtual)/reverse
core-js(-pure)/es|stable|actual|full/array(/virtual)/slice
core-js(-pure)/es|stable|actual|full/array(/virtual)/some
core-js(-pure)/es|stable|actual|full/array(/virtual)/sort
core-js(-pure)/es|stable|actual|full/array(/virtual)/splice
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-reversed
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-sorted
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-spliced
core-js(-pure)/es|stable|actual|full/array(/virtual)/unshift
core-js(-pure)/es|stable|actual|full/array(/virtual)/values
core-js(-pure)/es|stable|actual|full/array(/virtual)/with

Examples:

Array.from(new Set([1, 2, 3, 2, 1]));        // => [1, 2, 3]
Array.from({ 0: 1, 1: 2, 2: 3, length: 3 }); // => [1, 2, 3]
Array.from('123', Number);                   // => [1, 2, 3]
Array.from('123', it => it * it);            // => [1, 4, 9]

Array.of(1);       // => [1]
Array.of(1, 2, 3); // => [1, 2, 3]

let array = ['a', 'b', 'c'];

for (let value of array) console.log(value);          // => 'a', 'b', 'c'
for (let value of array.values()) console.log(value); // => 'a', 'b', 'c'
for (let key of array.keys()) console.log(key);       // => 0, 1, 2
for (let [key, value] of array.entries()) {
  console.log(key);                                   // => 0, 1, 2
  console.log(value);                                 // => 'a', 'b', 'c'
}

function isOdd(value) {
  return value % 2;
}
[4, 8, 15, 16, 23, 42].find(isOdd);      // => 15
[4, 8, 15, 16, 23, 42].findIndex(isOdd); // => 2
[1, 2, 3, 4].findLast(isOdd);            // => 3
[1, 2, 3, 4].findLastIndex(isOdd);       // => 2

Array(5).fill(42); // => [42, 42, 42, 42, 42]

[1, 2, 3, 4, 5].copyWithin(0, 3); // => [4, 5, 3, 4, 5]

[1, 2, 3].includes(2);        // => true
[1, 2, 3].includes(4);        // => false
[1, 2, 3].includes(2, 2);     // => false

[NaN].indexOf(NaN);           // => -1
[NaN].includes(NaN);          // => true
Array(1).indexOf(undefined);  // => -1
Array(1).includes(undefined); // => true

[1, [2, 3], [4, 5]].flat();    // => [1, 2, 3, 4, 5]
[1, [2, [3, [4]]], 5].flat();  // => [1, 2, [3, [4]], 5]
[1, [2, [3, [4]]], 5].flat(3); // => [1, 2, 3, 4, 5]

[{ a: 1, b: 2 }, { a: 3, b: 4 }, { a: 5, b: 6 }].flatMap(it => [it.a, it.b]); // => [1, 2, 3, 4, 5, 6]

[1, 2, 3].at(1);  // => 2
[1, 2, 3].at(-1); // => 3

const sequence = [1, 2, 3];
sequence.toReversed(); // => [3, 2, 1]
sequence; // => [1, 2, 3]

const initialArray = [1, 2, 3, 4];
initialArray.toSpliced(1, 2, 5, 6, 7); // => [1, 5, 6, 7, 4]
initialArray; // => [1, 2, 3, 4]

const outOfOrder = [3, 1, 2];
outOfOrder.toSorted(); // => [1, 2, 3]
outOfOrder; // => [3, 1, 2]

const correctionNeeded = [1, 1, 3];
correctionNeeded.with(1, 2); // => [1, 2, 3]
correctionNeeded; // => [1, 1, 3]

ECMAScript: Iterator

Modules es.iterator.constructor, es.iterator.drop, es.iterator.every, es.iterator.filter, es.iterator.find, es.iterator.flat-map, es.iterator.for-each, es.iterator.from, es.iterator.map, es.iterator.reduce, es.iterator.some, es.iterator.take, es.iterator.to-array

class Iterator {
  static from(iterable: Iterable<any> | Iterator<any>): Iterator<any>;
  drop(limit: uint): Iterator<any>;
  every(callbackfn: (value: any, counter: uint) => boolean): boolean;
  filter(callbackfn: (value: any, counter: uint) => boolean): Iterator<any>;
  find(callbackfn: (value: any, counter: uint) => boolean)): any;
  flatMap(callbackfn: (value: any, counter: uint) => Iterable<any> | Iterator<any>): Iterator<any>;
  forEach(callbackfn: (value: any, counter: uint) => void): void;
  map(callbackfn: (value: any, counter: uint) => any): Iterator<any>;
  reduce(callbackfn: (memo: any, value: any, counter: uint) => any, initialValue: any): any;
  some(callbackfn: (value: any, counter: uint) => boolean): boolean;
  take(limit: uint): Iterator<any>;
  toArray(): Array<any>;
  @@toStringTag: 'Iterator'
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/iterator
core-js(-pure)/es|stable|actual|full/iterator/drop
core-js(-pure)/es|stable|actual|full/iterator/every
core-js(-pure)/es|stable|actual|full/iterator/filter
core-js(-pure)/es|stable|actual|full/iterator/find
core-js(-pure)/es|stable|actual|full/iterator/flat-map
core-js(-pure)/es|stable|actual|full/iterator/for-each
core-js(-pure)/es|stable|actual|full/iterator/from
core-js(-pure)/es|stable|actual|full/iterator/map
core-js(-pure)/es|stable|actual|full/iterator/reduce
core-js(-pure)/es|stable|actual|full/iterator/some
core-js(-pure)/es|stable|actual|full/iterator/take
core-js(-pure)/es|stable|actual|full/iterator/to-array

Examples:

[1, 2, 3, 4, 5, 6, 7].values()
  .drop(1)
  .take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

Iterator.from({
  next: () => ({ done: Math.random() > 0.9, value: Math.random() * 10 | 0 }),
}).toArray(); // => [7, 6, 3, 0, 2, 8]

[!WARNING]

ECMAScript: String and RegExp

The main part of String features: modules es.string.from-code-point, es.string.raw, es.string.iterator, es.string.split, es.string.code-point-at, es.string.ends-with, es.string.includes, es.string.repeat, es.string.pad-start, es.string.pad-end, es.string.starts-with, es.string.trim, es.string.trim-start, es.string.trim-end, es.string.match-all, es.string.replace-all, es.string.at-alternative, es.string.is-well-formed, es.string.to-well-formed.

Adding support of well-known symbols @@match, @@replace, @@search and @@split and direct .exec calls to related String methods, modules es.string.match, es.string.replace, es.string.search and es.string.split.

Annex B methods. Modules es.string.anchor, es.string.big, es.string.blink, es.string.bold, es.string.fixed, es.string.fontcolor, es.string.fontsize, es.string.italics, es.string.link, es.string.small, es.string.strike, es.string.sub, es.string.sup, es.string.substr, es.escape and es.unescape.

RegExp features: modules es.regexp.constructor, es.regexp.dot-all, es.regexp.flags, es.regexp.sticky and es.regexp.test.

class String {
  static fromCodePoint(...codePoints: Array<number>): string;
  static raw({ raw: Array<string> }, ...substitutions: Array<string>): string;
  at(index: int): string;
  includes(searchString: string, position?: number): boolean;
  startsWith(searchString: string, position?: number): boolean;
  endsWith(searchString: string, position?: number): boolean;
  repeat(count: number): string;
  padStart(length: number, fillStr?: string = ' '): string;
  padEnd(length: number, fillStr?: string = ' '): string;
  codePointAt(pos: number): number | void;
  match(template: any): any; // ES2015+ fix for support @@match
  matchAll(regexp: RegExp): Iterator;
  replace(template: any, replacer: any): any; // ES2015+ fix for support @@replace
  replaceAll(searchValue: string | RegExp, replaceString: string | (searchValue, index, this) => string): string;
  search(template: any): any; // ES2015+ fix for support @@search
  split(template: any, limit?: int): Array<string>;; // ES2015+ fix for support @@split, some fixes for old engines
  trim(): string;
  trimLeft(): string;
  trimRight(): string;
  trimStart(): string;
  trimEnd(): string;
  isWellFormed(): boolean;
  toWellFormed(): string;
  anchor(name: string): string;
  big(): string;
  blink(): string;
  bold(): string;
  fixed(): string;
  fontcolor(color: string): string;
  fontsize(size: any): string;
  italics(): string;
  link(url: string): string;
  small(): string;
  strike(): string;
  sub(): string;
  substr(start: int, length?: int): string;
  sup(): string;
  @@iterator(): Iterator<characters>;
}

class RegExp {
  // support of sticky (`y`) flag, dotAll (`s`) flag, named capture groups, can alter flags
  constructor(pattern: RegExp | string, flags?: string): RegExp;
  exec(): Array<string | undefined> | null; // IE8 fixes
  test(string: string): boolean; // delegation to `.exec`
  toString(): string; // ES2015+ fix - generic
  @@match(string: string): Array | null;
  @@matchAll(string: string): Iterator;
  @@replace(string: string, replaceValue: Function | string): string;
  @@search(string: string): number;
  @@split(string: string, limit: number): Array<string>;
  readonly attribute dotAll: boolean; // IE9+
  readonly attribute flags: string;   // IE9+
  readonly attribute sticky: boolean; // IE9+
}

function escape(string: string): string;
function unescape(string: string): string;

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/string
core-js(-pure)/es|stable|actual|full/string/from-code-point
core-js(-pure)/es|stable|actual|full/string/raw
core-js/es|stable|actual|full/string/match
core-js/es|stable|actual|full/string/replace
core-js/es|stable|actual|full/string/search
core-js/es|stable|actual|full/string/split
core-js(-pure)/es|stable|actual/string(/virtual)/at
core-js(-pure)/es|stable|actual|full/string(/virtual)/code-point-at
core-js(-pure)/es|stable|actual|full/string(/virtual)/ends-with
core-js(-pure)/es|stable|actual|full/string(/virtual)/includes
core-js(-pure)/es|stable|actual|full/string(/virtual)/starts-with
core-js(-pure)/es|stable|actual|full/string(/virtual)/match-all
core-js(-pure)/es|stable|actual|full/string(/virtual)/pad-start
core-js(-pure)/es|stable|actual|full/string(/virtual)/pad-end
core-js(-pure)/es|stable|actual|full/string(/virtual)/repeat
core-js(-pure)/es|stable|actual|full/string(/virtual)/replace-all
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-start
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-end
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-left
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-right
core-js(-pure)/es|stable|actual|full/string(/virtual)/is-well-formed
core-js(-pure)/es|stable|actual|full/string(/virtual)/to-well-formed
core-js(-pure)/es|stable|actual|full/string(/virtual)/anchor
core-js(-pure)/es|stable|actual|full/string(/virtual)/big
core-js(-pure)/es|stable|actual|full/string(/virtual)/blink
core-js(-pure)/es|stable|actual|full/string(/virtual)/bold
core-js(-pure)/es|stable|actual|full/string(/virtual)/fixed
core-js(-pure)/es|stable|actual|full/string(/virtual)/fontcolor
core-js(-pure)/es|stable|actual|full/string(/virtual)/fontsize
core-js(-pure)/es|stable|actual|full/string(/virtual)/italics
core-js(-pure)/es|stable|actual|full/string(/virtual)/link
core-js(-pure)/es|stable|actual|full/string(/virtual)/small
core-js(-pure)/es|stable|actual|full/string(/virtual)/strike
core-js(-pure)/es|stable|actual|full/string(/virtual)/sub
core-js(-pure)/es|stable|actual|full/string(/virtual)/substr
core-js(-pure)/es|stable|actual|full/string(/virtual)/sup
core-js(-pure)/es|stable|actual|full/string(/virtual)/iterator
core-js/es|stable|actual|full/regexp
core-js/es|stable|actual|full/regexp/constructor
core-js/es|stable|actual|full/regexp/dot-all
core-js(-pure)/es|stable|actual|full/regexp/flags
core-js/es|stable|actual|full/regexp/sticky
core-js/es|stable|actual|full/regexp/test
core-js/es|stable|actual|full/regexp/to-string
core-js/es|stable|actual|full/escape
core-js/es|stable|actual|full/unescape

Examples:

for (let value of 'a𠮷b') {
  console.log(value); // => 'a', '𠮷', 'b'
}

'foobarbaz'.includes('bar');      // => true
'foobarbaz'.includes('bar', 4);   // => false
'foobarbaz'.startsWith('foo');    // => true
'foobarbaz'.startsWith('bar', 3); // => true
'foobarbaz'.endsWith('baz');      // => true
'foobarbaz'.endsWith('bar', 6);   // => true

'string'.repeat(3); // => 'stringstringstring'

'hello'.padStart(10);         // => '     hello'
'hello'.padStart(10, '1234'); // => '12341hello'
'hello'.padEnd(10);           // => 'hello     '
'hello'.padEnd(10, '1234');   // => 'hello12341'

'𠮷'.codePointAt(0); // => 134071
String.fromCodePoint(97, 134071, 98); // => 'a𠮷b'

let name = 'Bob';
String.raw`Hi\n${ name }!`;           // => 'Hi\\nBob!' (ES2015 template string syntax)
String.raw({ raw: 'test' }, 0, 1, 2); // => 't0e1s2t'

'foo'.bold();                      // => '<b>foo</b>'
'bar'.anchor('a"b');               // => '<a name="a&quot;b">bar</a>'
'baz'.link('https://example.com'); // => '<a href="https://example.com">baz</a>'

RegExp('.', 's').test('\n'); // => true
RegExp('.', 's').dotAll;     // => true

RegExp('foo:(?<foo>\\w+),bar:(?<bar>\\w+)').exec('foo:abc,bar:def').groups; // => { foo: 'abc', bar: 'def' }

'foo:abc,bar:def'.replace(RegExp('foo:(?<foo>\\w+),bar:(?<bar>\\w+)'), '$<bar>,$<foo>'); // => 'def,abc'

// eslint-disable-next-line regexp/no-useless-flag -- example
RegExp(/./g, 'm'); // => /./m

/foo/.flags;   // => ''
/foo/gi.flags; // => 'gi'

RegExp('foo', 'y').sticky; // => true

const text = 'First line\nSecond line';
const regex = RegExp('(?<index>\\S+) line\\n?', 'y');

regex.exec(text).groups.index; // => 'First'
regex.exec(text).groups.index; // => 'Second'
regex.exec(text);    // => null

'foo'.match({ [Symbol.match]: () => 1 });     // => 1
'foo'.replace({ [Symbol.replace]: () => 2 }); // => 2
'foo'.search({ [Symbol.search]: () => 3 });   // => 3
'foo'.split({ [Symbol.split]: () => 4 });     // => 4

RegExp.prototype.toString.call({ source: 'foo', flags: 'bar' }); // => '/foo/bar'

'   hello   '.trimLeft();  // => 'hello   '
'   hello   '.trimRight(); // => '   hello'
'   hello   '.trimStart(); // => 'hello   '
'   hello   '.trimEnd();   // => '   hello'

for (let { groups: { number, letter } } of '1111a2b3cccc'.matchAll(RegExp('(?<number>\\d)(?<letter>\\D)', 'g'))) {
  console.log(number, letter); // => 1 a, 2 b, 3 c
}

'Test abc test test abc test.'.replaceAll('abc', 'foo'); // -> 'Test foo test test foo test.'

'abc'.at(1);  // => 'b'
'abc'.at(-1); // => 'c'

'a💩b'.isWellFormed();      // => true
'a\uD83Db'.isWellFormed();  // => false

'a💩b'.toWellFormed();      // => 'a💩b'
'a\uD83Db'.toWellFormed();  // => 'a�b'

ECMAScript: Number

Module es.number.constructor. Number constructor support binary and octal literals, example:

Number('0b1010101'); // => 85
Number('0o7654321'); // => 2054353

Modules es.number.epsilon, es.number.is-finite, es.number.is-integer, es.number.is-nan, es.number.is-safe-integer, es.number.max-safe-integer, es.number.min-safe-integer, es.number.parse-float, es.number.parse-int, es.number.to-exponential, es.number.to-fixed, es.number.to-precision, es.parse-int, es.parse-float.

class Number {
  constructor(value: any): number;
  toExponential(digits: number): string;
  toFixed(digits: number): string;
  toPrecision(precision: number): string;
  static isFinite(number: any): boolean;
  static isNaN(number: any): boolean;
  static isInteger(number: any): boolean;
  static isSafeInteger(number: any): boolean;
  static parseFloat(string: string): number;
  static parseInt(string: string, radix?: number = 10): number;
  static EPSILON: number;
  static MAX_SAFE_INTEGER: number;
  static MIN_SAFE_INTEGER: number;
}

function parseFloat(string: string): number;
function parseInt(string: string, radix?: number = 10): number;

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/number
core-js(-pure)/es|stable|actual|full/number/constructor
core-js(-pure)/es|stable|actual|full/number/is-finite
core-js(-pure)/es|stable|actual|full/number/is-nan
core-js(-pure)/es|stable|actual|full/number/is-integer
core-js(-pure)/es|stable|actual|full/number/is-safe-integer
core-js(-pure)/es|stable|actual|full/number/parse-float
core-js(-pure)/es|stable|actual|full/number/parse-int
core-js(-pure)/es|stable|actual|full/number/epsilon
core-js(-pure)/es|stable|actual|full/number/max-safe-integer
core-js(-pure)/es|stable|actual|full/number/min-safe-integer
core-js(-pure)/es|stable|actual|full/number(/virtual)/to-exponential
core-js(-pure)/es|stable|actual|full/number(/virtual)/to-fixed
core-js(-pure)/es|stable|actual|full/number(/virtual)/to-precision
core-js(-pure)/es|stable|actual|full/parse-float
core-js(-pure)/es|stable|actual|full/parse-int

ECMAScript: Math

Modules es.math.acosh, es.math.asinh, es.math.atanh, es.math.cbrt, es.math.clz32, es.math.cosh, es.math.expm1, es.math.fround, es.math.hypot, es.math.imul, es.math.log10, es.math.log1p, es.math.log2, es.math.sign, es.math.sinh, es.math.tanh, es.math.trunc.

namespace Math {
  acosh(number: number): number;
  asinh(number: number): number;
  atanh(number: number): number;
  cbrt(number: number): number;
  clz32(number: number): number;
  cosh(number: number): number;
  expm1(number: number): number;
  fround(number: number): number;
  hypot(...args: Array<number>): number;
  imul(number1: number, number2: number): number;
  log1p(number: number): number;
  log10(number: number): number;
  log2(number: number): number;
  sign(number: number): 1 | -1 | 0 | -0 | NaN;
  sinh(number: number): number;
  tanh(number: number): number;
  trunc(number: number): number;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/math
core-js(-pure)/es|stable|actual|full/math/acosh
core-js(-pure)/es|stable|actual|full/math/asinh
core-js(-pure)/es|stable|actual|full/math/atanh
core-js(-pure)/es|stable|actual|full/math/cbrt
core-js(-pure)/es|stable|actual|full/math/clz32
core-js(-pure)/es|stable|actual|full/math/cosh
core-js(-pure)/es|stable|actual|full/math/expm1
core-js(-pure)/es|stable|actual|full/math/fround
core-js(-pure)/es|stable|actual|full/math/hypot
core-js(-pure)/es|stable|actual|full/math/imul
core-js(-pure)/es|stable|actual|full/math/log1p
core-js(-pure)/es|stable|actual|full/math/log10
core-js(-pure)/es|stable|actual|full/math/log2
core-js(-pure)/es|stable|actual|full/math/sign
core-js(-pure)/es|stable|actual|full/math/sinh
core-js(-pure)/es|stable|actual|full/math/tanh
core-js(-pure)/es|stable|actual|full/math/trunc

ECMAScript: Date

Modules es.date.to-string, ES5 features with fixes: es.date.now, es.date.to-iso-string, es.date.to-json and es.date.to-primitive.

Annex B methods. Modules es.date.get-year, es.date.set-year and es.date.to-gmt-string.

class Date {
  getYear(): int;
  setYear(year: int): number;
  toGMTString(): string;
  toISOString(): string;
  toJSON(): string;
  toString(): string;
  @@toPrimitive(hint: 'default' | 'number' | 'string'): string | number;
  static now(): number;
}

CommonJS entry points:

core-js/es|stable|actual|full/date
core-js/es|stable|actual|full/date/to-string
core-js(-pure)/es|stable|actual|full/date/now
core-js(-pure)/es|stable|actual|full/date/get-year
core-js(-pure)/es|stable|actual|full/date/set-year
core-js(-pure)/es|stable|actual|full/date/to-gmt-string
core-js(-pure)/es|stable|actual|full/date/to-iso-string
core-js(-pure)/es|stable|actual|full/date/to-json
core-js(-pure)/es|stable|actual|full/date/to-primitive

Example:

new Date(NaN).toString(); // => 'Invalid Date'

ECMAScript: Promise

Modules es.promise, es.promise.all-settled, es.promise.any, es.promise.finally, es.promise.try and es.promise.with-resolvers.

class Promise {
  constructor(executor: (resolve: Function, reject: Function) => void): Promise;
  then(onFulfilled: Function, onRejected: Function): Promise;
  catch(onRejected: Function): Promise;
  finally(onFinally: Function): Promise;
  static all(iterable: Iterable): Promise;
  static allSettled(iterable: Iterable): Promise;
  static any(promises: Iterable): Promise;
  static race(iterable: Iterable): Promise;
  static reject(r: any): Promise;
  static resolve(x: any): Promise;
  static try(callbackfn: Function, ...args?: Array<mixed>): Promise;
  static withResolvers(): { promise: Promise, resolve: function, reject: function };
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/promise
core-js(-pure)/es|stable|actual|full/promise/all-settled
core-js(-pure)/es|stable|actual|full/promise/any
core-js(-pure)/es|stable|actual|full/promise/finally
core-js(-pure)/es|stable|actual|full/promise/try
core-js(-pure)/es|stable|actual|full/promise/with-resolvers

Basic example:

/* eslint-disable promise/prefer-await-to-callbacks -- example */
function sleepRandom(time) {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, time * 1e3, 0 | Math.random() * 1e3);
  });
}

console.log('Run');                    // => Run
sleepRandom(5).then(result => {
  console.log(result);                 // => 869, after 5 sec.
  return sleepRandom(10);
}).then(result => {
  console.log(result);                 // => 202, after 10 sec.
}).then(() => {
  console.log('immediately after');    // => immediately after
  throw new Error('Irror!');
}).then(() => {
  console.log('will not be displayed');
}).catch(error => console.log(error)); // => => Error: Irror!

Promise.resolve and Promise.reject example:

/* eslint-disable promise/prefer-await-to-callbacks -- example */
Promise.resolve(42).then(x => console.log(x));         // => 42
Promise.reject(42).catch(error => console.log(error)); // => 42

Promise.resolve($.getJSON('/data.json')); // => ES promise

Promise#finally example:

Promise.resolve(42).finally(() => console.log('You will see it anyway'));

Promise.reject(42).finally(() => console.log('You will see it anyway'));

Promise.all example:

Promise.all([
  'foo',
  sleepRandom(5),
  sleepRandom(15),
  sleepRandom(10),            // after 15 sec:
]).then(x => console.log(x)); // => ['foo', 956, 85, 382]

Promise.race example:

/* eslint-disable promise/prefer-await-to-callbacks -- example */
function timeLimit(promise, time) {
  return Promise.race([promise, new Promise((resolve, reject) => {
    setTimeout(reject, time * 1e3, new Error(`Await > ${ time } sec`));
  })]);
}

timeLimit(sleepRandom(5), 10).then(x => console.log(x));           // => 853, after 5 sec.
timeLimit(sleepRandom(15), 10).catch(error => console.log(error)); // Error: Await > 10 sec

Promise.allSettled example:

Promise.allSettled([
  Promise.resolve(1),
  Promise.reject(2),
  Promise.resolve(3),
]).then(console.log); // => [{ value: 1, status: 'fulfilled' }, { reason: 2, status: 'rejected' }, { value: 3, status: 'fulfilled' }]

Promise.any example:

Promise.any([
  Promise.resolve(1),
  Promise.reject(2),
  Promise.resolve(3),
]).then(console.log); // => 1

Promise.any([
  Promise.reject(1),
  Promise.reject(2),
  Promise.reject(3),
]).catch(({ errors }) => console.log(errors)); // => [1, 2, 3]

Promise.try examples:

/* eslint-disable promise/prefer-await-to-callbacks -- example */
Promise.try(() => 42).then(it => console.log(`Promise, resolved as ${ it }`));

Promise.try(() => { throw new Error('42'); }).catch(error => console.log(`Promise, rejected as ${ error }`));

Promise.try(async () => 42).then(it => console.log(`Promise, resolved as ${ it }`));

Promise.try(async () => { throw new Error('42'); }).catch(error => console.log(`Promise, rejected as ${ error }`));

Promise.try(it => it, 42).then(it => console.log(`Promise, resolved as ${ it }`));

Promise.withResolvers examples:

const d = Promise.withResolvers();
d.resolve(42);
d.promise.then(console.log); // => 42

Example with async functions:

let delay = time => new Promise(resolve => setTimeout(resolve, time));

async function sleepRandom(time) {
  await delay(time * 1e3);
  return 0 | Math.random() * 1e3;
}

async function sleepError(time, msg) {
  await delay(time * 1e3);
  throw new Error(msg);
}

(async () => {
  try {
    console.log('Run');                // => Run
    console.log(await sleepRandom(5)); // => 936, after 5 sec.
    let [a, b, c] = await Promise.all([
      sleepRandom(5),
      sleepRandom(15),
      sleepRandom(10),
    ]);
    console.log(a, b, c);              // => 210 445 71, after 15 sec.
    await sleepError(5, 'Error!');
    console.log('Will not be displayed');
  } catch (error) {
    console.log(error);                // => Error: 'Error!', after 5 sec.
  }
})();
Unhandled rejection tracking

In Node.js, like in native implementation, available events unhandledRejection and rejectionHandled:

process.on('unhandledRejection', (reason, promise) => console.log('unhandled', reason, promise));
process.on('rejectionHandled', promise => console.log('handled', promise));

let promise = Promise.reject(42);
// unhandled 42 [object Promise]

// eslint-disable-next-line promise/prefer-await-to-then -- example
setTimeout(() => promise.catch(() => { /* empty */ }), 1e3);
// handled [object Promise]

In a browser on rejection, by default, you will see notify in the console, or you can add a custom handler and a handler on handling unhandled, example:

globalThis.addEventListener('unhandledrejection', e => console.log('unhandled', e.reason, e.promise));
globalThis.addEventListener('rejectionhandled', e => console.log('handled', e.reason, e.promise));
// or
globalThis.onunhandledrejection = e => console.log('unhandled', e.reason, e.promise);
globalThis.onrejectionhandled = e => console.log('handled', e.reason, e.promise);

let promise = Promise.reject(42);
// => unhandled 42 [object Promise]

// eslint-disable-next-line promise/prefer-await-to-then -- example
setTimeout(() => promise.catch(() => { /* empty */ }), 1e3);
// => handled 42 [object Promise]

ECMAScript: Symbol

Modules es.symbol, es.symbol.async-iterator, es.symbol.description, es.symbol.has-instance, es.symbol.is-concat-spreadable, es.symbol.iterator, es.symbol.match, es.symbol.replace, es.symbol.search, es.symbol.species, es.symbol.split, es.symbol.to-primitive, es.symbol.to-string-tag, es.symbol.unscopables, es.math.to-string-tag.

class Symbol {
  constructor(description?): symbol;
  readonly attribute description: string | void;
  static asyncIterator: @@asyncIterator;
  static hasInstance: @@hasInstance;
  static isConcatSpreadable: @@isConcatSpreadable;
  static iterator: @@iterator;
  static match: @@match;
  static replace: @@replace;
  static search: @@search;
  static species: @@species;
  static split: @@split;
  static toPrimitive: @@toPrimitive;
  static toStringTag: @@toStringTag;
  static unscopables: @@unscopables;
  static for(key: string): symbol;
  static keyFor(sym: symbol): string;
  static useSimple(): void;
  static useSetter(): void;
}

class Object {
  static getOwnPropertySymbols(object: any): Array<symbol>;
}

Also wrapped some methods for correct work with Symbol polyfill.

class Object {
  static create(prototype: Object | null, properties?: { [property: PropertyKey]: PropertyDescriptor }): Object;
  static defineProperties(object: Object, properties: { [property: PropertyKey]: PropertyDescriptor })): Object;
  static defineProperty(object: Object, property: PropertyKey, attributes: PropertyDescriptor): Object;
  static getOwnPropertyDescriptor(object: any, property: PropertyKey): PropertyDescriptor | void;
  static getOwnPropertyNames(object: any): Array<string>;
  propertyIsEnumerable(key: PropertyKey): boolean;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/symbol
core-js(-pure)/es|stable|actual|full/symbol/async-iterator
core-js/es|stable|actual|full/symbol/description
core-js(-pure)/es|stable|actual|full/symbol/has-instance
core-js(-pure)/es|stable|actual|full/symbol/is-concat-spreadable
core-js(-pure)/es|stable|actual|full/symbol/iterator
core-js(-pure)/es|stable|actual|full/symbol/match
core-js(-pure)/es|stable|actual|full/symbol/replace
core-js(-pure)/es|stable|actual|full/symbol/search
core-js(-pure)/es|stable|actual|full/symbol/species
core-js(-pure)/es|stable|actual|full/symbol/split
core-js(-pure)/es|stable|actual|full/symbol/to-primitive
core-js(-pure)/es|stable|actual|full/symbol/to-string-tag
core-js(-pure)/es|stable|actual|full/symbol/unscopables
core-js(-pure)/es|stable|actual|full/symbol/for
core-js(-pure)/es|stable|actual|full/symbol/key-for
core-js(-pure)/es|stable|actual|full/object/get-own-property-symbols
core-js(-pure)/es|stable|actual|full/math/to-string-tag

Basic example:

let Person = (() => {
  let NAME = Symbol('name');
  return class {
    constructor(name) {
      this[NAME] = name;
    }
    getName() {
      return this[NAME];
    }
  };
})();

let person = new Person('Vasya');
console.log(person.getName());            // => 'Vasya'
console.log(person.name);                 // => undefined
console.log(person[Symbol('name')]);      // => undefined, symbols are uniq
for (let key in person) console.log(key); // => nothing, symbols are not enumerable

Symbol.for & Symbol.keyFor example:

let symbol = Symbol.for('key');
symbol === Symbol.for('key'); // true
Symbol.keyFor(symbol);        // 'key'

Example with methods for getting own object keys:

let object = { a: 1 };
Object.defineProperty(object, 'b', { value: 2 });
object[Symbol('c')] = 3;
Object.keys(object);                  // => ['a']
Object.getOwnPropertyNames(object);   // => ['a', 'b']
Object.getOwnPropertySymbols(object); // => [Symbol(c)]
Reflect.ownKeys(object);              // => ['a', 'b', Symbol(c)]

Symbol#description getter:

Symbol('foo').description; // => 'foo'
// eslint-disable-next-line symbol-description -- example
Symbol().description;      // => undefined
Caveats when using Symbol polyfill:

You can disable defining setters in Object.prototype. Example:

Symbol.useSimple();
let symbol1 = Symbol('symbol1');
let object1 = {};
object1[symbol1] = true;
for (let key in object1) console.log(key); // => 'Symbol(symbol1)_t.qamkg9f3q', w/o native Symbol

Symbol.useSetter();
let symbol2 = Symbol('symbol2');
let object2 = {};
object2[symbol2] = true;
for (let key in object2) console.log(key); // nothing

ECMAScript: Collections

core-js uses native collections in most cases, just fixes methods / constructor, if it's required, and in the old environment uses fast polyfill (O(1) lookup).

Map

Modules es.map and es.map.group-by.

class Map {
  constructor(iterable?: Iterable<[key, value]>): Map;
  clear(): void;
  delete(key: any): boolean;
  forEach(callbackfn: (value: any, key: any, target: any) => void, thisArg: any): void;
  get(key: any): any;
  has(key: any): boolean;
  set(key: any, val: any): this;
  values(): Iterator<value>;
  keys(): Iterator<key>;
  entries(): Iterator<[key, value]>;
  @@iterator(): Iterator<[key, value]>;
  readonly attribute size: number;
  static groupBy(items: Iterable, callbackfn: (value: any, index: number) => key): Map<key, Array<mixed>>;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/map
core-js(-pure)/es|stable|actual|full/map/group-by

Examples:

let array = [1];

let map = new Map([['a', 1], [42, 2]]);
map.set(array, 3).set(true, 4);

console.log(map.size);        // => 4
console.log(map.has(array));  // => true
console.log(map.has([1]));    // => false
console.log(map.get(array));  // => 3
map.forEach((val, key) => {
  console.log(val);           // => 1, 2, 3, 4
  console.log(key);           // => 'a', 42, [1], true
});
map.delete(array);
console.log(map.size);        // => 3
console.log(map.get(array));  // => undefined
console.log(Array.from(map)); // => [['a', 1], [42, 2], [true, 4]]

map = new Map([['a', 1], ['b', 2], ['c', 3]]);

for (let [key, value] of map) {
  console.log(key);                                 // => 'a', 'b', 'c'
  console.log(value);                               // => 1, 2, 3
}
for (let value of map.values()) console.log(value); // => 1, 2, 3
for (let key of map.keys()) console.log(key);       // => 'a', 'b', 'c'
for (let [key, value] of map.entries()) {
  console.log(key);                                 // => 'a', 'b', 'c'
  console.log(value);                               // => 1, 2, 3
}

map = Map.groupBy([1, 2, 3, 4, 5], it => it % 2);
map.get(1); // => [1, 3, 5]
map.get(0); // => [2, 4]

Set

Modules es.set, es.set.difference.v2, es.set.intersection.v2, es.set.is-disjoint-from.v2, es.set.is-subset-of.v2, es.set.is-superset-of.v2, es.set.symmetric-difference.v2, es.set.union.v2

class Set {
  constructor(iterable?: Iterable<value>): Set;
  add(key: any): this;
  clear(): void;
  delete(key: any): boolean;
  forEach((value: any, key: any, target: any) => void, thisArg: any): void;
  has(key: any): boolean;
  values(): Iterator<value>;
  keys(): Iterator<value>;
  entries(): Iterator<[value, value]>;
  difference(other: SetLike<mixed>): Set;
  intersection(other: SetLike<mixed>): Set;
  isDisjointFrom(other: SetLike<mixed>): boolean;
  isSubsetOf(other: SetLike<mixed>): boolean;
  isSupersetOf(other: SetLike<mixed>): boolean;
  symmetricDifference(other: SetLike<mixed>): Set;
  union(other: SetLike<mixed>): Set;
  @@iterator(): Iterator<value>;
  readonly attribute size: number;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/set
core-js(-pure)/es|stable|actual|full/set/difference
core-js(-pure)/es|stable|actual|full/set/intersection
core-js(-pure)/es|stable|actual|full/set/is-disjoint-from
core-js(-pure)/es|stable|actual|full/set/is-subset-of
core-js(-pure)/es|stable|actual|full/set/is-superset-of
core-js(-pure)/es|stable|actual|full/set/symmetric-difference
core-js(-pure)/es|stable|actual|full/set/union

Examples:

let set = new Set(['a', 'b', 'a', 'c']);
set.add('d').add('b').add('e');
console.log(set.size);        // => 5
console.log(set.has('b'));    // => true
set.forEach(it => {
  console.log(it);            // => 'a', 'b', 'c', 'd', 'e'
});
set.delete('b');
console.log(set.size);        // => 4
console.log(set.has('b'));    // => false
console.log(Array.from(set)); // => ['a', 'c', 'd', 'e']

set = new Set([1, 2, 3, 2, 1]);

for (let value of set) console.log(value);          // => 1, 2, 3
for (let value of set.values()) console.log(value); // => 1, 2, 3
for (let key of set.keys()) console.log(key);       // => 1, 2, 3
for (let [key, value] of set.entries()) {
  console.log(key);                                 // => 1, 2, 3
  console.log(value);                               // => 1, 2, 3
}

new Set([1, 2, 3]).union(new Set([3, 4, 5]));               // => Set {1, 2, 3, 4, 5}
new Set([1, 2, 3]).intersection(new Set([3, 4, 5]));        // => Set {3}
new Set([1, 2, 3]).difference(new Set([3, 4, 5]));          // => Set {1, 2}
new Set([1, 2, 3]).symmetricDifference(new Set([3, 4, 5])); // => Set {1, 2, 4, 5}
new Set([1, 2, 3]).isDisjointFrom(new Set([4, 5, 6]));      // => true
new Set([1, 2, 3]).isSubsetOf(new Set([5, 4, 3, 2, 1]));    // => true
new Set([5, 4, 3, 2, 1]).isSupersetOf(new Set([1, 2, 3]));  // => true

WeakMap

Module es.weak-map.

class WeakMap {
  constructor(iterable?: Iterable<[key, value]>): WeakMap;
  delete(key: Object): boolean;
  get(key: Object): any;
  has(key: Object): boolean;
  set(key: Object, val: any): this;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/weak-map

Examples:

let a = [1];
let b = [2];
let c = [3];

let weakmap = new WeakMap([[a, 1], [b, 2]]);
weakmap.set(c, 3).set(b, 4);
console.log(weakmap.has(a));   // => true
console.log(weakmap.has([1])); // => false
console.log(weakmap.get(a));   // => 1
weakmap.delete(a);
console.log(weakmap.get(a));   // => undefined

// Private properties store:
let Person = (() => {
  let names = new WeakMap();
  return class {
    constructor(name) {
      names.set(this, name);
    }
    getName() {
      return names.get(this);
    }
  };
})();

let person = new Person('Vasya');
console.log(person.getName());            // => 'Vasya'
for (let key in person) console.log(key); // => only 'getName'

WeakSet

Module es.weak-set.

class WeakSet {
  constructor(iterable?: Iterable<value>): WeakSet;
  add(key: Object): this;
  delete(key: Object): boolean;
  has(key: Object): boolean;
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/weak-set

Examples:

let a = [1];
let b = [2];
let c = [3];

let weakset = new WeakSet([a, b, a]);
weakset.add(c).add(b).add(c);
console.log(weakset.has(b));   // => true
console.log(weakset.has([2])); // => false
weakset.delete(b);
console.log(weakset.has(b));   // => false

[!WARNING]

ECMAScript: Typed Arrays

Implementations and fixes for ArrayBuffer, DataView, Typed Arrays constructors, static and prototype methods. Typed arrays work only in environments with support descriptors (IE9+), ArrayBuffer and DataView should work anywhere.

Modules es.array-buffer.constructor, es.array-buffer.is-view, esnext.array-buffer.detached, es.array-buffer.slice, esnext.array-buffer.transfer, esnext.array-buffer.transfer-to-fixed-length es.data-view, es.typed-array.int8-array, es.typed-array.uint8-array, es.typed-array.uint8-clamped-array, es.typed-array.int16-array, es.typed-array.uint16-array, es.typed-array.int32-array, es.typed-array.uint32-array, es.typed-array.float32-array, es.typed-array.float64-array, es.typed-array.copy-within, es.typed-array.every, es.typed-array.fill, es.typed-array.filter, es.typed-array.find, es.typed-array.find-index, es.typed-array.find-last, es.typed-array.find-last-index, es.typed-array.for-each, es.typed-array.from, es.typed-array.includes, es.typed-array.index-of, es.typed-array.iterator, es.typed-array.last-index-of, es.typed-array.map, es.typed-array.of, es.typed-array.reduce, es.typed-array.reduce-right, es.typed-array.reverse, es.typed-array.set, es.typed-array.slice, es.typed-array.some, es.typed-array.sort, es.typed-array.subarray, es.typed-array.to-locale-string, es.typed-array.to-string, es.typed-array.at, es.typed-array.to-reversed, es.typed-array.to-sorted, es.typed-array.with.

class ArrayBuffer {
  constructor(length: any): ArrayBuffer;
  readonly attribute byteLength: number;
  readonly attribute detached: boolean;
  slice(start: any, end: any): ArrayBuffer;
  transfer(newLength?: number): ArrayBuffer;
  transferToFixedLength(newLength?: number): ArrayBuffer;
  static isView(arg: any): boolean;
}

class DataView {
  constructor(buffer: ArrayBuffer, byteOffset?: number, byteLength?: number): DataView;
  getInt8(offset: any): int8;
  getUint8(offset: any): uint8
  getInt16(offset: any, littleEndian?: boolean = false): int16;
  getUint16(offset: any, littleEndian?: boolean = false): uint16;
  getInt32(offset: any, littleEndian?: boolean = false): int32;
  getUint32(offset: any, littleEndian?: boolean = false): uint32;
  getFloat32(offset: any, littleEndian?: boolean = false): float32;
  getFloat64(offset: any, littleEndian?: boolean = false): float64;
  setInt8(offset: any, value: any): void;
  setUint8(offset: any, value: any): void;
  setInt16(offset: any, value: any, littleEndian?: boolean = false): void;
  setUint16(offset: any, value: any, littleEndian?: boolean = false): void;
  setInt32(offset: any, value: any, littleEndian?: boolean = false): void;
  setUint32(offset: any, value: any, littleEndian?: boolean = false): void;
  setFloat32(offset: any, value: any, littleEndian?: boolean = false): void;
  setFloat64(offset: any, value: any, littleEndian?: boolean = false): void;
  readonly attribute buffer: ArrayBuffer;
  readonly attribute byteLength: number;
  readonly attribute byteOffset: number;
}

class [
  Int8Array,
  Uint8Array,
  Uint8ClampedArray,
  Int16Array,
  Uint16Array,
  Int32Array,
  Uint32Array,
  Float32Array,
  Float64Array,
] extends %TypedArray% {
  constructor(length: number): %TypedArray%;
  constructor(object: %TypedArray% | Iterable | ArrayLike): %TypedArray%;
  constructor(buffer: ArrayBuffer, byteOffset?: number, length?: number): %TypedArray%
}

class %TypedArray% {
  at(index: int): number;
  copyWithin(target: number, start: number, end?: number): this;
  entries(): Iterator<[index, value]>;
  every(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean, thisArg?: any): boolean;
  fill(value: number, start?: number, end?: number): this;
  filter(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean, thisArg?: any): %TypedArray%;
  find(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean), thisArg?: any): any;
  findIndex(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean, thisArg?: any): uint;
  findLast(callbackfn: (value: any, index: number, target: %TypedArray%) => boolean, thisArg?: any): any;
  findLastIndex(callbackfn: (value: any, index: number, target: %TypedArray%) => boolean, thisArg?: any): uint;
  forEach(callbackfn: (value: number, index: number, target: %TypedArray%) => void, thisArg?: any): void;
  includes(searchElement: any, from?: number): boolean;
  indexOf(searchElement: any, from?: number): number;
  join(separator: string = ','): string;
  keys(): Iterator<index>;
  lastIndexOf(searchElement: any, from?: number): number;
  map(mapFn: (value: number, index: number, target: %TypedArray%) => number, thisArg?: any): %TypedArray%;
  reduce(callbackfn: (memo: any, value: number, index: number, target: %TypedArray%) => any, initialValue?: any): any;
  reduceRight(callbackfn: (memo: any, value: number, index: number, target: %TypedArray%) => any, initialValue?: any): any;
  reverse(): this;
  set(array: ArrayLike, offset?: number): void;
  slice(start?: number, end?: number): %TypedArray%;
  some(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean, thisArg?: any): boolean;
  sort(comparefn?: (a: number, b: number) => number): this; // with modern behavior like stable sort
  subarray(begin?: number, end?: number): %TypedArray%;
  toReversed(): %TypedArray%;
  toSorted(comparefn?: (a: any, b: any) => number): %TypedArray%;
  toString(): string;
  toLocaleString(): string;
  values(): Iterator<value>;
  with(index: includes, value: any): %TypedArray%;
  @@iterator(): Iterator<value>;
  readonly attribute buffer: ArrayBuffer;
  readonly attribute byteLength: number;
  readonly attribute byteOffset: number;
  readonly attribute length: number;
  BYTES_PER_ELEMENT: number;
  static from(items: Iterable | ArrayLike, mapFn?: (value: any, index: number) => any, thisArg?: any): %TypedArray%;
  static of(...args: Array<mixed>): %TypedArray%;
  static BYTES_PER_ELEMENT: number;
}

CommonJS entry points:

core-js/es|stable|actual|full/array-buffer
core-js/es|stable|actual|full/array-buffer/constructor
core-js/es|stable|actual|full/array-buffer/is-view
core-js/es|stable|actual|full/array-buffer/detached
core-js/es|stable|actual|full/array-buffer/slice
core-js/es|stable|actual|full/array-buffer/transfer
core-js/es|stable|actual|full/array-buffer/transfer-to-fixed-length
core-js/es|stable|actual|full/data-view
core-js/es|stable|actual|full/typed-array
core-js/es|stable|actual|full/typed-array/int8-array
core-js/es|stable|actual|full/typed-array/uint8-array
core-js/es|stable|actual|full/typed-array/uint8-clamped-array
core-js/es|stable|actual|full/typed-array/int16-array
core-js/es|stable|actual|full/typed-array/uint16-array
core-js/es|stable|actual|full/typed-array/int32-array
core-js/es|stable|actual|full/typed-array/uint32-array
core-js/es|stable|actual|full/typed-array/float32-array
core-js/es|stable|actual|full/typed-array/float64-array
core-js/es|stable|actual|full/typed-array/at
core-js/es|stable|actual|full/typed-array/copy-within
core-js/es|stable|actual|full/typed-array/entries
core-js/es|stable|actual|full/typed-array/every
core-js/es|stable|actual|full/typed-array/fill
core-js/es|stable|actual|full/typed-array/filter
core-js/es|stable|actual|full/typed-array/find
core-js/es|stable|actual|full/typed-array/find-index
core-js/es|stable|actual|full/typed-array/find-last
core-js/es|stable|actual|full/typed-array/find-last-index
core-js/es|stable|actual|full/typed-array/for-each
core-js/es|stable|actual|full/typed-array/from
core-js/es|stable|actual|full/typed-array/includes
core-js/es|stable|actual|full/typed-array/index-of
core-js/es|stable|actual|full/typed-array/iterator
core-js/es|stable|actual|full/typed-array/join
core-js/es|stable|actual|full/typed-array/keys
core-js/es|stable|actual|full/typed-array/last-index-of
core-js/es|stable|actual|full/typed-array/map
core-js/es|stable|actual|full/typed-array/of
core-js/es|stable|actual|full/typed-array/reduce
core-js/es|stable|actual|full/typed-array/reduce-right
core-js/es|stable|actual|full/typed-array/reverse
core-js/es|stable|actual|full/typed-array/set
core-js/es|stable|actual|full/typed-array/slice
core-js/es|stable|actual|full/typed-array/some
core-js/es|stable|actual|full/typed-array/sort
core-js/es|stable|actual|full/typed-array/subarray
core-js/es|stable|actual|full/typed-array/to-locale-string
core-js/es|stable|actual|full/typed-array/to-reversed
core-js/es|stable|actual|full/typed-array/to-sorted
core-js/es|stable|actual|full/typed-array/to-string
core-js/es|stable|actual|full/typed-array/values
core-js/es|stable|actual|full/typed-array/with

Examples:

new Int32Array(4);                          // => [0, 0, 0, 0]
new Uint8ClampedArray([1, 2, 3, 666]);      // => [1, 2, 3, 255]
new Float32Array(new Set([1, 2, 3, 2, 1])); // => [1, 2, 3]

let buffer = new ArrayBuffer(8);
let view = new DataView(buffer);
view.setFloat64(0, 123.456, true);
new Uint8Array(buffer.slice(4)); // => [47, 221, 94, 64]

Int8Array.of(1, 1.5, 5.7, 745);      // => [1, 1, 5, -23]
Uint8Array.from([1, 1.5, 5.7, 745]); // => [1, 1, 5, 233]

let typed = new Uint8Array([1, 2, 3]);

let a = typed.slice(1);    // => [2, 3]
typed.buffer === a.buffer; // => false
let b = typed.subarray(1); // => [2, 3]
typed.buffer === b.buffer; // => true

typed.filter(it => it % 2); // => [1, 3]
typed.map(it => it * 1.5);  // => [1, 3, 4]

for (let value of typed) console.log(value);          // => 1, 2, 3
for (let value of typed.values()) console.log(value); // => 1, 2, 3
for (let key of typed.keys()) console.log(key);       // => 0, 1, 2
for (let [key, value] of typed.entries()) {
  console.log(key);                                   // => 0, 1, 2
  console.log(value);                                 // => 1, 2, 3
}

new Int32Array([1, 2, 3]).at(1);  // => 2
new Int32Array([1, 2, 3]).at(-1); // => 3

buffer = Int8Array.of(1, 2, 3, 4, 5, 6, 7, 8).buffer;
console.log(buffer.byteLength); // => 8
console.log(buffer.detached); // => false
const newBuffer = buffer.transfer(4);
console.log(buffer.byteLength); // => 0
console.log(buffer.detached); // => true
console.log(newBuffer.byteLength); // => 4
console.log(newBuffer.detached); // => false
console.log([...new Int8Array(newBuffer)]); // => [1, 2, 3, 4]

[!WARNING]

ECMAScript: Reflect

Modules es.reflect.apply, es.reflect.construct, es.reflect.define-property, es.reflect.delete-property, es.reflect.get, es.reflect.get-own-property-descriptor, es.reflect.get-prototype-of, es.reflect.has, es.reflect.is-extensible, es.reflect.own-keys, es.reflect.prevent-extensions, es.reflect.set, es.reflect.set-prototype-of.

namespace Reflect {
  apply(target: Function, thisArgument: any, argumentsList: Array<mixed>): any;
  construct(target: Function, argumentsList: Array<mixed>, newTarget?: Function): Object;
  defineProperty(target: Object, propertyKey: PropertyKey, attributes: PropertyDescriptor): boolean;
  deleteProperty(target: Object, propertyKey: PropertyKey): boolean;
  get(target: Object, propertyKey: PropertyKey, receiver?: any): any;
  getOwnPropertyDescriptor(target: Object, propertyKey: PropertyKey): PropertyDescriptor | void;
  getPrototypeOf(target: Object): Object | null;
  has(target: Object, propertyKey: PropertyKey): boolean;
  isExtensible(target: Object): boolean;
  ownKeys(target: Object): Array<string | symbol>;
  preventExtensions(target: Object): boolean;
  set(target: Object, propertyKey: PropertyKey, V: any, receiver?: any): boolean;
  setPrototypeOf(target: Object, proto: Object | null): boolean; // required __proto__ - IE11+
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/reflect
core-js(-pure)/es|stable|actual|full/reflect/apply
core-js(-pure)/es|stable|actual|full/reflect/construct
core-js(-pure)/es|stable|actual|full/reflect/define-property
core-js(-pure)/es|stable|actual|full/reflect/delete-property
core-js(-pure)/es|stable|actual|full/reflect/get
core-js(-pure)/es|stable|actual|full/reflect/get-own-property-descriptor
core-js(-pure)/es|stable|actual|full/reflect/get-prototype-of
core-js(-pure)/es|stable|actual|full/reflect/has
core-js(-pure)/es|stable|actual|full/reflect/is-extensible
core-js(-pure)/es|stable|actual|full/reflect/own-keys
core-js(-pure)/es|stable|actual|full/reflect/prevent-extensions
core-js(-pure)/es|stable|actual|full/reflect/set
core-js(-pure)/es|stable|actual|full/reflect/set-prototype-of

Examples:

let object = { a: 1 };
Object.defineProperty(object, 'b', { value: 2 });
object[Symbol('c')] = 3;
Reflect.ownKeys(object); // => ['a', 'b', Symbol(c)]

function C(a, b) {
  this.c = a + b;
}

let instance = Reflect.construct(C, [20, 22]);
instance.c; // => 42

ECMAScript: JSON

Since JSON object is missed only in very old engines like IE7-, core-js does not provide a full JSON polyfill, however, fix already existing implementations by the current standard, for example, well-formed JSON.stringify. JSON is also fixed in other modules - for example, Symbol polyfill fixes JSON.stringify for correct work with symbols.

Module es.json.to-string-tag and es.json.stringify.

namespace JSON {
  stringify(value: any, replacer?: Array<string | number> | (this: any, key: string, value: any) => any, space?: string | number): string | void;
  @@toStringTag: 'JSON';
}

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/json/stringify
core-js(-pure)/es|stable|actual|full/json/to-string-tag

Examples:

JSON.stringify({ '𠮷': ['\uDF06\uD834'] }); // => '{"𠮷":["\\udf06\\ud834"]}'

ECMAScript: globalThis

Module es.global-this.

let globalThis: GlobalThisValue;

CommonJS entry points:

core-js(-pure)/es|stable|actual|full/global-this

Examples:

globalThis.Array === Array; // => true

ECMAScript proposals

The TC39 process.

core-js/stage/3 entry point contains only stage 3 proposals, core-js/stage/2.7 - stage 2.7 and stage 3, etc.

Finished proposals

Finished (stage 4) proposals already marked in core-js as stable ECMAScript, they are available in core-js/stable and core-js/es namespace, you can find them in related sections of the README. However, even for finished proposals, core-js provides a way to include only features for a specific proposal like core-js/proposals/proposal-name.

globalThis
let globalThis: GlobalThisValue;

CommonJS entry points:

core-js/proposals/global-this
Relative indexing method
class Array {
  at(index: int): any;
}

class String {
  at(index: int): string;
}

class %TypedArray% {
  at(index: int): number;
}

CommonJS entry points:

core-js/proposals/relative-indexing-method
Array.prototype.includes
class Array {
  includes(searchElement: any, from?: number): boolean;
}

class %TypedArray% {
  includes(searchElement: any, from?: number): boolean;
}

CommonJS entry points:

core-js/proposals/array-includes
Array.prototype.flat / Array.prototype.flatMap
class Array {
  flat(depthArg?: number = 1): Array<mixed>;
  flatMap(mapFn: (value: any, index: number, target: any) => any, thisArg: any): Array<mixed>;
}

CommonJS entry points:

core-js/proposals/array-flat-map
Array find from last
class Array {
  findLast(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): any;
  findLastIndex(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): uint;
}

class %TypedArray% {
  findLast(callbackfn: (value: any, index: number, target: %TypedArray%) => boolean, thisArg?: any): any;
  findLastIndex(callbackfn: (value: any, index: number, target: %TypedArray%) => boolean, thisArg?: any): uint;
}

CommonJS entry points:

core-js/proposals/array-find-from-last
Change Array by copy
class Array {
  toReversed(): Array<mixed>;
  toSpliced(start?: number, deleteCount?: number, ...items: Array<mixed>): Array<mixed>;
  toSorted(comparefn?: (a: any, b: any) => number): Array<mixed>;
  with(index: includes, value: any): Array<mixed>;
}

class %TypedArray% {
  toReversed(): %TypedArray%;
  toSorted(comparefn?: (a: any, b: any) => number): %TypedArray%;
  with(index: includes, value: any): %TypedArray%;
}

CommonJS entry points:

core-js/proposals/change-array-by-copy-stage-4
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-reversed
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-sorted
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-spliced
core-js(-pure)/es|stable|actual|full/array(/virtual)/with
core-js/es|stable|actual|full/typed-array/to-reversed
core-js/es|stable|actual|full/typed-array/to-sorted
core-js/es|stable|actual|full/typed-array/with
Array grouping
class Object {
  static groupBy(items: Iterable, callbackfn: (value: any, index: number) => key): { [key]: Array<mixed> };
}

class Map {
  static groupBy(items: Iterable, callbackfn: (value: any, index: number) => key): Map<key, Array<mixed>>;
}

CommonJS entry points:

core-js/proposals/array-grouping-v2
ArrayBuffer.prototype.transfer and friends
class ArrayBuffer {
  readonly attribute detached: boolean;
  transfer(newLength?: number): ArrayBuffer;
  transferToFixedLength(newLength?: number): ArrayBuffer;
}

CommonJS entry points:

core-js/proposals/array-buffer-transfer
Iterator helpers
class Iterator {
  static from(iterable: Iterable<any> | Iterator<any>): Iterator<any>;
  drop(limit: uint): Iterator<any>;
  every(callbackfn: (value: any, counter: uint) => boolean): boolean;
  filter(callbackfn: (value: any, counter: uint) => boolean): Iterator<any>;
  find(callbackfn: (value: any, counter: uint) => boolean)): any;
  flatMap(callbackfn: (value: any, counter: uint) => Iterable<any> | Iterator<any>): Iterator<any>;
  forEach(callbackfn: (value: any, counter: uint) => void): void;
  map(callbackfn: (value: any, counter: uint) => any): Iterator<any>;
  reduce(callbackfn: (memo: any, value: any, counter: uint) => any, initialValue: any): any;
  some(callbackfn: (value: any, counter: uint) => boolean): boolean;
  take(limit: uint): Iterator<any>;
  toArray(): Array<any>;
  @@toStringTag: 'Iterator'
}

CommonJS entry points:

core-js/proposals/iterator-helpers-stage-3-2
Object.values / Object.entries
class Object {
  static entries(object: Object): Array<[string, mixed]>;
  static values(object: any): Array<mixed>;
}

CommonJS entry points:

core-js/proposals/object-values-entries
Object.fromEntries
class Object {
  static fromEntries(iterable: Iterable<[key, value]>): Object;
}

CommonJS entry points:

core-js/proposals/object-from-entries
Object.getOwnPropertyDescriptors
class Object {
  static getOwnPropertyDescriptors(object: any): { [property: PropertyKey]: PropertyDescriptor };
}

CommonJS entry points:

core-js/proposals/object-getownpropertydescriptors
Accessible Object.prototype.hasOwnProperty
class Object {
  static hasOwn(object: object, key: PropertyKey): boolean;
}

CommonJS entry points:

core-js/proposals/accessible-object-hasownproperty
String padding
class String {
  padStart(length: number, fillStr?: string = ' '): string;
  padEnd(length: number, fillStr?: string = ' '): string;
}

CommonJS entry points:

core-js/proposals/string-padding
String#matchAll.
class String {
  matchAll(regexp: RegExp): Iterator;
}

CommonJS entry points:

core-js/proposals/string-match-all
String#replaceAll
class String {
  replaceAll(searchValue: string | RegExp, replaceString: string | (searchValue, index, this) => string): string;
}

CommonJS entry points:

core-js/proposals/string-replace-all-stage-4
String.prototype.trimStart / String.prototype.trimEnd
class String {
  trimLeft(): string;
  trimRight(): string;
  trimStart(): string;
  trimEnd(): string;
}

CommonJS entry points:

core-js/proposals/string-left-right-trim
RegExp s (dotAll) flag
// patched for support `RegExp` dotAll (`s`) flag:
class RegExp {
  constructor(pattern: RegExp | string, flags?: string): RegExp;
  exec(): Array<string | undefined> | null;
  readonly attribute dotAll: boolean;
  readonly attribute flags: string;
}

CommonJS entry points:

core-js/proposals/regexp-dotall-flag
RegExp named capture groups
// patched for support `RegExp` named capture groups:
class RegExp {
  constructor(pattern: RegExp | string, flags?: string): RegExp;
  exec(): Array<string | undefined> | null;
  @@replace(string: string, replaceValue: Function | string): string;
}

CommonJS entry points:

core-js/proposals/regexp-named-groups
Promise.allSettled
class Promise {
  static allSettled(iterable: Iterable): Promise;
}

CommonJS entry points:

core-js/proposals/promise-all-settled
Promise.any
class AggregateError {
  constructor(errors: Iterable, message: string): AggregateError;
  errors: Array<any>;
  message: string;
}

class Promise {
  static any(promises: Iterable): Promise<any>;
}

CommonJS entry points:

core-js/proposals/promise-any
Promise.prototype.finally
class Promise {
  finally(onFinally: Function): Promise;
}

CommonJS entry points:

core-js/proposals/promise-finally
Promise.try
class Promise {
  static try(callbackfn: Function, ...args?: Array<mixed>): Promise;
}

CommonJS entry points:

core-js/proposals/promise-try
Promise.withResolvers
class Promise {
  static withResolvers(): { promise: Promise, resolve: function, reject: function };
}

CommonJS entry points:

core-js/proposals/promise-with-resolvers
Symbol.asyncIterator for asynchronous iteration
class Symbol {
  static asyncIterator: @@asyncIterator;
}

CommonJS entry points:

core-js/proposals/async-iteration
Symbol.prototype.description
class Symbol {
  readonly attribute description: string | void;
}

CommonJS entry points:

core-js/proposals/symbol-description
Well-formed JSON.stringify
namespace JSON {
  stringify(target: any, replacer?: Function | Array, space?: string | number): string | void;
}

CommonJS entry points:

core-js/proposals/well-formed-stringify
Well-formed unicode strings
class String {
  isWellFormed(): boolean;
  toWellFormed(): string;
}

CommonJS entry points:

core-js/proposals/well-formed-unicode-strings
New Set methods
class Set {
  difference(other: SetLike<mixed>): Set;
  intersection(other: SetLike<mixed>): Set;
  isDisjointFrom(other: SetLike<mixed>): boolean;
  isSubsetOf(other: SetLike<mixed>): boolean;
  isSupersetOf(other: SetLike<mixed>): boolean;
  symmetricDifference(other: SetLike<mixed>): Set;
  union(other: SetLike<mixed>): Set;
}

CommonJS entry points:

core-js/proposals/set-methods-v2

Stage 3 proposals

CommonJS entry points:

core-js(-pure)/stage/3

##### [`Array.fromAsync`](https://github.com/tc39/proposal-array-from-async)[⬆](#index)
Modules [`esnext.array.from-async`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.array.from-async.js).
```ts
class Array {
  static fromAsync(asyncItems: AsyncIterable | Iterable | ArrayLike, mapfn?: (value: any, index: number) => any, thisArg?: any): Array;
}

CommonJS entry points:

core-js/proposals/array-from-async-stage-2
core-js(-pure)/actual|full/array/from-async

Example:

await Array.fromAsync((async function * () { yield * [1, 2, 3]; })(), i => i * i); // => [1, 4, 9]
JSON.parse source text access

Modules esnext.json.is-raw-json, esnext.json.parse, esnext.json.raw-json.

namespace JSON {
  isRawJSON(O: any): boolean;
  // patched for source support
  parse(text: string, reviver?: (this: any, key: string, value: any, context: { source?: string }) => any): any;
  rawJSON(text: any): RawJSON;
  // patched for `JSON.rawJSON` support
  stringify(value: any, replacer?: Array<string | number> | (this: any, key: string, value: any) => any, space?: string | number): string | void;
}

CommonJS entry points:

core-js/proposals/json-parse-with-source
core-js(-pure)/actual|full/json/is-raw-json
core-js(-pure)/actual|full/json/parse
core-js(-pure)/actual|full/json/raw-json
core-js(-pure)/actual|full/json/stringify

Examples:

function digitsToBigInt(key, val, { source }) {
  return /^\d+$/.test(source) ? BigInt(source) : val;
}

function bigIntToRawJSON(key, val) {
  return typeof val === 'bigint' ? JSON.rawJSON(String(val)) : val;
}

const tooBigForNumber = BigInt(Number.MAX_SAFE_INTEGER) + 2n;
JSON.parse(String(tooBigForNumber), digitsToBigInt) === tooBigForNumber; // true

const wayTooBig = BigInt(`1${ '0'.repeat(1000) }`);
JSON.parse(String(wayTooBig), digitsToBigInt) === wayTooBig; // true

const embedded = JSON.stringify({ tooBigForNumber }, bigIntToRawJSON);
embedded === '{"tooBigForNumber":9007199254740993}'; // true
Float16 methods

Modules esnext.data-view.get-float16, esnext.data-view.set-float16 and esnext.math.f16round

class DataView {
  getFloat16(offset: any): number
  setFloat16(offset: any, value: any): void;
}

namespace Math {
  fround(number: any): number;
}

CommonJS entry points:

core-js/proposals/float16
core-js/actual|full/dataview/get-float16
core-js/actual|full/dataview/set-float16
core-js/actual|full/math/f16round

Examples:

console.log(Math.f16round(1.337)); // => 1.3369140625

const view = new DataView(new ArrayBuffer(2));
view.setFloat16(0, 1.337);
console.log(view.getFloat16(0)); // => 1.3369140625
Uint8Array to / from base64 and hex

Modules esnext.uint8-array.from-base64, esnext.uint8-array.from-hex, esnext.uint8-array.set-from-hex, esnext.uint8-array.to-base64, esnext.uint8-array.to-hex.

class Uint8Array {
  static fromBase64(string: string, options?: { alphabet?: 'base64' | 'base64url', lastChunkHandling?: 'loose' | 'strict' | 'stop-before-partial' }): Uint8Array;
  static fromHex(string: string): Uint8Array;
  setFromBase64(string: string, options?: { alphabet?: 'base64' | 'base64url', lastChunkHandling?: 'loose' | 'strict' | 'stop-before-partial' }): { read: uint, written: uint };
  setFromHex(string: string): { read: uint, written: uint };
  toBase64(options?: { alphabet?: 'base64' | 'base64url', omitPadding?: boolean }): string;
  toHex(): string;
}

CommonJS entry points:

core-js/proposals/array-buffer-base64
core-js(-pure)/actual|full/typed-array/from-base64
core-js(-pure)/actual|full/typed-array/from-hex
core-js(-pure)/actual|full/typed-array/set-from-base64
core-js(-pure)/actual|full/typed-array/set-from-hex
core-js(-pure)/actual|full/typed-array/to-base64
core-js(-pure)/actual|full/typed-array/to-hex

Example:

let arr = new Uint8Array([72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100]);
console.log(arr.toBase64()); // => 'SGVsbG8gV29ybGQ='
console.log(arr.toBase64({ omitPadding: true })); // => 'SGVsbG8gV29ybGQ'
console.log(arr.toHex()); // => '48656c6c6f20576f726c64'
console.log(Uint8Array.fromBase64('SGVsbG8gV29ybGQ=')); // => Uint8Array([72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100])
console.log(Uint8Array.fromHex('48656c6c6f20576f726c64')); // => Uint8Array([72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100])
Explicit Resource Management

[!NOTE] This is only built-ins for this proposal, using syntax support requires transpiler support.

Modules esnext.symbol.dispose, esnext.disposable-stack.constructor, esnext.suppressed-error.constructor, esnext.iterator.dispose, esnext.symbol.async-dispose, esnext.async-disposable-stack.constructor, esnext.async-iterator.async-dispose.

class Symbol {
  static asyncDispose: @@asyncDispose;
  static dispose: @@dispose;
}

class DisposableStack {
  constructor(): DisposableStack;
  dispose(): undefined;
  use(value: Disposable): value;
  adopt(value: object, onDispose: Function): value;
  defer(onDispose: Function): undefined;
  @@dispose(): undefined;
  @@toStringTag: 'DisposableStack';
}

class AsyncDisposableStack {
  constructor(): AsyncDisposableStack;
  disposeAsync(): Promise<undefined>;
  use(value: AsyncDisposable | Disposable): value;
  adopt(value: object, onDispose: Function): value;
  defer(onDispose: Function): undefined;
  @@asyncDispose(): Promise<undefined>;
  @@toStringTag: 'AsyncDisposableStack';
}

class SuppressedError extends Error {
  constructor(error: any, suppressed: any, message?: string): SuppressedError;
  error: any;
  suppressed: any;
  message: string;
  cause: any;
}

class Iterator {
  @@dispose(): undefined;
}

class AsyncIterator {
  @@asyncDispose(): Promise<undefined>;
}

CommonJS entry points:

core-js/proposals/explicit-resource-management
core-js(-pure)/actual|full/symbol/async-dispose
core-js(-pure)/actual|full/symbol/dispose
core-js(-pure)/actual|full/disposable-stack
core-js(-pure)/actual|full/async-disposable-stack
core-js(-pure)/actual|full/suppressed-error
core-js(-pure)/actual|full/iterator/dispose
core-js(-pure)/actual|full/async-iterator/async-dispose
RegExp escaping

Module esnext.regexp.escape

class RegExp {
  static escape(value: string): string
}

CommonJS entry points:

core-js/proposals/regexp-escaping
core-js(-pure)/actual|full/regexp/escape

Example:

console.log(RegExp.escape('10$')); // => '\\x310\\$'
console.log(RegExp.escape('abcdefg_123456')); // => '\\x61bcdefg_123456'
console.log(RegExp.escape('Привет')); // => 'Привет'
console.log(RegExp.escape('(){}[]|,.?*+-^$=<>\\/#&!%:;@~\'"`'));
// => '\\(\\)\\{\\}\\[\\]\\|\\x2c\\.\\?\\*\\+\\x2d\\^\\$\\x3d\\x3c\\x3e\\\\\\/\\x23\\x26\\x21\\x25\\x3a\\x3b\\x40\\x7e\\x27\\x22\\x60'
console.log(RegExp.escape('\u0009\u000A\u000B\u000C\u000D\u0020\u00A0\u1680\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF'));
// => '\\\t\\\n\\\v\\\f\\\r\\x20\\xa0\\u1680\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u202f\\u205f\\u3000\\u2028\\u2029\\ufeff'
console.log(RegExp.escape('💩')); // => '💩'
console.log(RegExp.escape('\uD83D')); // => '\\ud83d'
Math.sumPrecise

Module esnext.math.sum-precise

class Math {
  static sumPrecise(items: Iterable<number>): Number;
}

CommonJS entry points:

core-js/proposals/math-sum
core-js(-pure)/full|actual/math/sum-precise

Examples:

1e20 + 0.1 + -1e20; // => 0
Math.sumPrecise([1e20, 0.1, -1e20]); // => 0.1
Symbol.metadata for decorators metadata proposal

Modules esnext.symbol.metadata and esnext.function.metadata.

class Symbol {
  static metadata: @@metadata;
}

class Function {
  @@metadata: null;
}

CommonJS entry points:

core-js/proposals/decorator-metadata-v2
core-js(-pure)/actual|full/symbol/metadata
core-js(-pure)/actual|full/function/metadata

Stage 2.7 proposals

CommonJS entry points:

core-js(-pure)/stage/2.7
Iterator sequencing

Module esnext.iterator.concat

class Iterator {
  concat(...items: Array<IterableObject>): Iterator<any>;
}

CommonJS entry points:

core-js/proposals/iterator-sequencing
core-js(-pure)/full/iterator/concat

Example:

Iterator.concat([0, 1].values(), [2, 3], function * () {
  yield 4;
  yield 5;
}()).toArray(); // => [0, 1, 2, 3, 4, 5]

Stage 2 proposals

CommonJS entry points:

core-js(-pure)/stage/2
AsyncIterator helpers

Modules esnext.async-iterator.constructor, esnext.async-iterator.drop, esnext.async-iterator.every, esnext.async-iterator.filter, esnext.async-iterator.find, esnext.async-iterator.flat-map, esnext.async-iterator.for-each, esnext.async-iterator.from, esnext.async-iterator.map, esnext.async-iterator.reduce, esnext.async-iterator.some, esnext.async-iterator.take, esnext.async-iterator.to-array, , esnext.iterator.to-async

class Iterator {
  toAsync(): AsyncIterator<any>;
}

class AsyncIterator {
  static from(iterable: AsyncIterable<any> | Iterable<any> | AsyncIterator<any>): AsyncIterator<any>;
  drop(limit: uint): AsyncIterator<any>;
  every(async callbackfn: (value: any, counter: uint) => boolean): Promise<boolean>;
  filter(async callbackfn: (value: any, counter: uint) => boolean): AsyncIterator<any>;
  find(async callbackfn: (value: any, counter: uint) => boolean)): Promise<any>;
  flatMap(async callbackfn: (value: any, counter: uint) => AsyncIterable<any> | Iterable<any> | AsyncIterator<any>): AsyncIterator<any>;
  forEach(async callbackfn: (value: any, counter: uint) => void): Promise<void>;
  map(async callbackfn: (value: any, counter: uint) => any): AsyncIterator<any>;
  reduce(async callbackfn: (memo: any, value: any, counter: uint) => any, initialValue: any): Promise<any>;
  some(async callbackfn: (value: any, counter: uint) => boolean): Promise<boolean>;
  take(limit: uint): AsyncIterator<any>;
  toArray(): Promise<Array>;
  @@toStringTag: 'AsyncIterator'
}

CommonJS entry points:

core-js/proposals/async-iterator-helpers
core-js(-pure)/actual|full/async-iterator
core-js(-pure)/actual|full/async-iterator/drop
core-js(-pure)/actual|full/async-iterator/every
core-js(-pure)/actual|full/async-iterator/filter
core-js(-pure)/actual|full/async-iterator/find
core-js(-pure)/actual|full/async-iterator/flat-map
core-js(-pure)/actual|full/async-iterator/for-each
core-js(-pure)/actual|full/async-iterator/from
core-js(-pure)/actual|full/async-iterator/map
core-js(-pure)/actual|full/async-iterator/reduce
core-js(-pure)/actual|full/async-iterator/some
core-js(-pure)/actual|full/async-iterator/take
core-js(-pure)/actual|full/async-iterator/to-array
core-js(-pure)/actual|full/iterator/to-async

Examples:

await AsyncIterator.from([1, 2, 3, 4, 5, 6, 7])
  .drop(1)
  .take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray(); // => [9, 25]

await [1, 2, 3].values().toAsync().map(async it => it ** 2).toArray(); // => [1, 4, 9]
Caveats:
const configurator = require('core-js/configurator');

configurator({ USE_FUNCTION_CONSTRUCTOR: true });

require('core-js/actual/async-iterator');

(async function * () { /* empty */ })() instanceof AsyncIterator; // => true
const configurator = require('core-js/configurator');

const { getPrototypeOf } = Object;

configurator({ AsyncIteratorPrototype: getPrototypeOf(getPrototypeOf(getPrototypeOf(async function * () { /* empty */ }()))) });

require('core-js/actual/async-iterator');

(async function * () { /* empty */ })() instanceof AsyncIterator; // => true
Iterator.range

Module esnext.iterator.range

class Iterator {
  range(start: number, end: number, options: { step: number = 1, inclusive: boolean = false } | step: number = 1): NumericRangeIterator;
  range(start: bigint, end: bigint | Infinity | -Infinity, options: { step: bigint = 1n, inclusive: boolean = false } | step: bigint = 1n): NumericRangeIterator;
}

CommonJS entry points:

core-js/proposals/number-range
core-js(-pure)/full/iterator/range

Example:

for (const i of Iterator.range(1, 10)) {
  console.log(i); // => 1, 2, 3, 4, 5, 6, 7, 8, 9
}

for (const i of Iterator.range(1, 10, { step: 3, inclusive: true })) {
  console.log(i); // => 1, 4, 7, 10
}
Map upsert

Modules esnext.map.get-or-insert, esnext.map.get-or-insert-computed, esnext.weak-map.get-or-insert and esnext.weak-map.get-or-insert-computed

class Map {
  getOrInsert(key: any, value: any): any;
  getOrInsertComputed(key: any, (key: any) => value: any): any;
}

class WeakMap {
  getOrInsert(key: any, value: any): any;
  getOrInsertComputed(key: any, (key: any) => value: any): any;
}

CommonJS entry points:

core-js/proposals/map-upsert-v4
core-js(-pure)/full/map/get-or-insert
core-js(-pure)/full/map/get-or-insert-computed
core-js(-pure)/full/weak-map/get-or-insert
core-js(-pure)/full/weak-map/get-or-insert-computed

Examples:

const map = new Map([['a', 1]]);

map.getOrInsert('a', 2); // => 1

map.getOrInsert('b', 3); // => 3

map.getOrInsertComputed('a', key => key); // => 1

map.getOrInsertComputed('c', key => key); // => 'c'

console.log(map); // => Map { 'a': 1, 'b': 3, 'c': 'c' }
Array.isTemplateObject

Module esnext.array.is-template-object

class Array {
  static isTemplateObject(value: any): boolean
}

CommonJS entry points:

core-js/proposals/array-is-template-object
core-js(-pure)/full/array/is-template-object

Example:

console.log(Array.isTemplateObject((it => it)`qwe${ 123 }asd`)); // => true
String.dedent

Module esnext.string.dedent

class String {
  static dedent(templateOrTag: { raw: Array<string> } | function, ...substitutions: Array<string>): string | function;
}

CommonJS entry points:

core-js/proposals/string-dedent
core-js(-pure)/full/string/dedent

Example:

const message = 42;

console.log(String.dedent`
  print('${ message }')
`); // => print('42')

String.dedent(console.log)`
  print('${ message }')
`; // => ["print('", "')", raw: Array(2)], 42
Symbol predicates

Modules esnext.symbol.is-registered-symbol, esnext.symbol.is-well-known-symbol.

class Symbol {
  static isRegisteredSymbol(value: any): boolean;
  static isWellKnownSymbol(value: any): boolean;
}

CommonJS entry points:

core-js/proposals/symbol-predicates-v2
core-js(-pure)/full/symbol/is-registered-symbol
core-js(-pure)/full/symbol/is-well-known-symbol

Example:

Symbol.isRegisteredSymbol(Symbol.for('key')); // => true
Symbol.isRegisteredSymbol(Symbol('key')); // => false

Symbol.isWellKnownSymbol(Symbol.iterator); // => true
Symbol.isWellKnownSymbol(Symbol('key')); // => false
Symbol.customMatcher for extractors

Module esnext.symbol.custom-matcher.

class Symbol {
  static customMatcher: @@customMatcher;
}

CommonJS entry points:

core-js/proposals/pattern-extractors
core-js(-pure)/full/symbol/custom-matcher

Stage 1 proposals

CommonJS entry points:

core-js(-pure)/stage/1
Observable

Modules esnext.observable and esnext.symbol.observable

class Observable {
  constructor(subscriber: Function): Observable;
  subscribe(observer: Function | { next?: Function, error?: Function, complete?: Function }): Subscription;
  @@observable(): this;
  static of(...items: Array<mixed>): Observable;
  static from(x: Observable | Iterable): Observable;
  static readonly attribute @@species: this;
}

class Symbol {
  static observable: @@observable;
}

CommonJS entry points:

core-js/proposals/observable
core-js(-pure)/full/observable
core-js(-pure)/full/symbol/observable

Examples:

new Observable(observer => {
  observer.next('hello');
  observer.next('world');
  observer.complete();
}).subscribe({
  next(it) { console.log(it); },
  complete() { console.log('!'); },
});
New collections methods

Modules esnext.set.add-all, esnext.set.delete-all, esnext.set.every, esnext.set.filter, esnext.set.find, esnext.set.join, esnext.set.map, esnext.set.reduce, esnext.set.some, esnext.map.delete-all, esnext.map.every, esnext.map.filter, esnext.map.find, esnext.map.find-key, esnext.map.includes, esnext.map.key-by, esnext.map.key-of, esnext.map.map-keys, esnext.map.map-values, esnext.map.merge, esnext.map.reduce, esnext.map.some, esnext.map.update, esnext.weak-set.add-all, esnext.weak-set.delete-all, esnext.weak-map.delete-all

.of and .from methods on collection constructors

Modules esnext.set.of, esnext.set.from, esnext.map.of, esnext.map.from, esnext.weak-set.of, esnext.weak-set.from, esnext.weak-map.of, esnext.weak-map.from

class Set {
  static of(...args: Array<mixed>): Set;
  static from(iterable: Iterable<mixed>, mapFn?: (value: any, index: number) => any, thisArg?: any): Set;
  addAll(...args: Array<mixed>): this;
  deleteAll(...args: Array<mixed>): boolean;
  every(callbackfn: (value: any, key: any, target: any) => boolean, thisArg?: any): boolean;
  filter(callbackfn: (value: any, key: any, target: any) => boolean, thisArg?: any): Set;
  find(callbackfn: (value: any, key: any, target: any) => boolean), thisArg?: any): any;
  join(separator: string = ','): string;
  map(callbackfn: (value: any, key: any, target: any) => any, thisArg?: any): Set;
  reduce(callbackfn: (memo: any, value: any, key: any, target: any) => any, initialValue?: any): any;
  some(callbackfn: (value: any, key: any, target: any) => boolean, thisArg?: any): boolean;
}

class Map {
  static of(...args: Array<[key, value]>): Map;
  static from(iterable: Iterable<mixed>, mapFn?: (value: any, index: number) => [key: any, value: any], thisArg?: any): Map;
  static keyBy(iterable: Iterable<mixed>, callbackfn?: (value: any) => any): Map;
  deleteAll(...args: Array<mixed>): boolean;
  every(callbackfn: (value: any, key: any, target: any) => boolean, thisArg?: any): boolean;
  filter(callbackfn: (value: any, key: any, target: any) => boolean, thisArg?: any): Map;
  find(callbackfn: (value: any, key: any, target: any) => boolean), thisArg?: any): any;
  findKey(callbackfn: (value: any, key: any, target: any) => boolean), thisArg?: any): any;
  includes(searchElement: any): boolean;
  keyOf(searchElement: any): any;
  mapKeys(mapFn: (value: any, index: number, target: any) => any, thisArg?: any): Map;
  mapValues(mapFn: (value: any, index: number, target: any) => any, thisArg?: any): Map;
  merge(...iterables: Array<Iterable>): this;
  reduce(callbackfn: (memo: any, value: any, key: any, target: any) => any, initialValue?: any): any;
  some(callbackfn: (value: any, key: any, target: any) => boolean, thisArg?: any): boolean;
  update(key: any, callbackfn: (value: any, key: any, target: any) => any, thunk?: (key: any, target: any) => any): this;
}

class WeakSet {
  static of(...args: Array<mixed>): WeakSet;
  static from(iterable: Iterable<mixed>, mapFn?: (value: any, index: number) => Object, thisArg?: any): WeakSet;
  addAll(...args: Array<mixed>): this;
  deleteAll(...args: Array<mixed>): boolean;
}

class WeakMap {
  static of(...args: Array<[key, value]>): WeakMap;
  static from(iterable: Iterable<mixed>, mapFn?: (value: any, index: number) => [key: Object, value: any], thisArg?: any): WeakMap;
  deleteAll(...args: Array<mixed>): boolean;
}

CommonJS entry points:

core-js/proposals/collection-methods
core-js/proposals/collection-of-from
core-js(-pure)/full/set/add-all
core-js(-pure)/full/set/delete-all
core-js(-pure)/full/set/every
core-js(-pure)/full/set/filter
core-js(-pure)/full/set/find
core-js(-pure)/full/set/from
core-js(-pure)/full/set/join
core-js(-pure)/full/set/map
core-js(-pure)/full/set/of
core-js(-pure)/full/set/reduce
core-js(-pure)/full/set/some
core-js(-pure)/full/map/delete-all
core-js(-pure)/full/map/every
core-js(-pure)/full/map/filter
core-js(-pure)/full/map/find
core-js(-pure)/full/map/find-key
core-js(-pure)/full/map/from
core-js(-pure)/full/map/includes
core-js(-pure)/full/map/key-by
core-js(-pure)/full/map/key-of
core-js(-pure)/full/map/map-keys
core-js(-pure)/full/map/map-values
core-js(-pure)/full/map/merge
core-js(-pure)/full/map/of
core-js(-pure)/full/map/reduce
core-js(-pure)/full/map/some
core-js(-pure)/full/map/update
core-js(-pure)/full/weak-set/add-all
core-js(-pure)/full/weak-set/delete-all
core-js(-pure)/full/weak-set/of
core-js(-pure)/full/weak-set/from
core-js(-pure)/full/weak-map/delete-all
core-js(-pure)/full/weak-map/of
core-js(-pure)/full/weak-map/from

.of / .from examples:

Set.of(1, 2, 3, 2, 1); // => Set {1, 2, 3}

Map.from([[1, 2], [3, 4]], ([key, value]) => [key ** 2, value ** 2]); // => Map { 1: 4, 9: 16 }
compositeKey and compositeSymbol

Modules esnext.composite-key and esnext.composite-symbol

function compositeKey(...args: Array<mixed>): object;
function compositeSymbol(...args: Array<mixed>): symbol;

CommonJS entry points:

core-js/proposals/keys-composition
core-js(-pure)/full/composite-key
core-js(-pure)/full/composite-symbol

Examples:

// returns a symbol
const symbol = compositeSymbol({});
console.log(typeof symbol); // => 'symbol'

// works the same, but returns a plain frozen object without a prototype
const key = compositeKey({});
console.log(typeof key); // => 'object'
console.log({}.toString.call(key)); // => '[object Object]'
console.log(Object.getPrototypeOf(key)); // => null
console.log(Object.isFrozen(key)); // => true

const a = ['a'];
const b = ['b'];
const c = ['c'];

/* eslint-disable no-self-compare -- example */
console.log(compositeSymbol(a) === compositeSymbol(a)); // => true
console.log(compositeSymbol(a) !== compositeSymbol(['a'])); // => true
console.log(compositeSymbol(a, 1) === compositeSymbol(a, 1)); // => true
console.log(compositeSymbol(a, b) !== compositeSymbol(b, a)); // => true
console.log(compositeSymbol(a, b, c) === compositeSymbol(a, b, c)); // => true
console.log(compositeSymbol(1, a) === compositeSymbol(1, a)); // => true
console.log(compositeSymbol(1, a, 2, b) === compositeSymbol(1, a, 2, b)); // => true
console.log(compositeSymbol(a, a) === compositeSymbol(a, a)); // => true
Array filtering

Modules esnext.array.filter-reject and esnext.typed-array.filter-reject.

class Array {
  filterReject(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): Array<mixed>;
}

class %TypedArray% {
  filterReject(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean, thisArg?: any): %TypedArray%;
}

CommonJS entry points:

core-js/proposals/array-filtering-stage-1
core-js(-pure)/full/array(/virtual)/filter-reject
core-js/full/typed-array/filter-reject

Examples:

[1, 2, 3, 4, 5].filterReject(it => it % 2); // => [2, 4]
Array deduplication

Modules esnext.array.unique-by and esnext.typed-array.unique-by

class Array {
  uniqueBy(resolver?: (item: any) => any): Array<mixed>;
}

class %TypedArray% {
  uniqueBy(resolver?: (item: any) => any): %TypedArray%;;
}

CommonJS entry points:

core-js/proposals/array-unique
core-js(-pure)/full/array(/virtual)/unique-by
core-js/full/typed-array/unique-by

Examples:

[1, 2, 3, 2, 1].uniqueBy(); // [1, 2, 3]

[
  { id: 1, uid: 10000 },
  { id: 2, uid: 10000 },
  { id: 3, uid: 10001 },
].uniqueBy(it => it.uid);    // => [{ id: 1, uid: 10000 }, { id: 3, uid: 10001 }]
DataView get / set Uint8Clamped methods

Modules esnext.data-view.get-uint8-clamped and esnext.data-view.set-uint8-clamped

class DataView {
  getUint8Clamped(offset: any): uint8
  setUint8Clamped(offset: any, value: any): void;
}

CommonJS entry points:

core-js/proposals/data-view-get-set-uint8-clamped
core-js/full/dataview/get-uint8-clamped
core-js/full/dataview/set-uint8-clamped

Examples:

const view = new DataView(new ArrayBuffer(1));
view.setUint8Clamped(0, 100500);
console.log(view.getUint8Clamped(0)); // => 255
Number.fromString

Module esnext.number.from-string

class Number {
  fromString(string: string, radix: number): number;
}

CommonJS entry points:

core-js/proposals/number-from-string
core-js(-pure)/full/number/from-string
String.cooked

Module esnext.string.cooked

class String {
  static cooked(template: Array<string>, ...substitutions: Array<string>): string;
}

CommonJS entry points:

core-js/proposals/string-cooked
core-js(-pure)/full/string/cooked

Example:

function safePath(strings, ...subs) {
  return String.cooked(strings, ...subs.map(sub => encodeURIComponent(sub)));
}

let id = 'spottie?';

safePath`/cats/${ id }`; // => /cats/spottie%3F
String.prototype.codePoints

Module esnext.string.code-points

class String {
  codePoints(): Iterator<{ codePoint, position }>;
}

CommonJS entry points:

core-js/proposals/string-code-points
core-js(-pure)/full/string/code-points

Example:

for (let { codePoint, position } of 'qwe'.codePoints()) {
  console.log(codePoint); // => 113, 119, 101
  console.log(position);  // => 0, 1, 2
}
Symbol.customMatcher for pattern matching

Module esnext.symbol.custom-matcher.

class Symbol {
  static customMatcher: @@customMatcher;
}

CommonJS entry points:

core-js/proposals/pattern-matching-v2
core-js(-pure)/full/symbol/custom-matcher

Stage 0 proposals

CommonJS entry points:

core-js(-pure)/stage/0
Function.prototype.demethodize

Module esnext.function.demethodize

class Function {
  demethodize(): Function;
}

CommonJS entry points:

core-js/proposals/function-demethodize
core-js(-pure)/full/function/demethodize
core-js(-pure)/full/function/virtual/demethodize

Examples:

const slice = Array.prototype.slice.demethodize();

slice([1, 2, 3], 1); // => [2, 3]
Function.{ isCallable, isConstructor }

Modules esnext.function.is-callable, esnext.function.is-constructor

class Function {
  static isCallable(value: any): boolean;
  static isConstructor(value: any): boolean;
}

CommonJS entry points:

core-js/proposals/function-is-callable-is-constructor
core-js(-pure)/full/function/is-callable
core-js(-pure)/full/function/is-constructor

Examples:

/* eslint-disable prefer-arrow-callback -- example */
Function.isCallable(null);                        // => false
Function.isCallable({});                          // => false
Function.isCallable(function () { /* empty */ }); // => true
Function.isCallable(() => { /* empty */ });       // => true
Function.isCallable(class { /* empty */ });       // => false

Function.isConstructor(null);                        // => false
Function.isConstructor({});                          // => false
Function.isConstructor(function () { /* empty */ }); // => true
Function.isConstructor(() => { /* empty */ });       // => false
Function.isConstructor(class { /* empty */ });       // => true

Pre-stage 0 proposals

CommonJS entry points:

core-js(-pure)/stage/pre
Reflect metadata

Modules esnext.reflect.define-metadata, esnext.reflect.delete-metadata, esnext.reflect.get-metadata, esnext.reflect.get-metadata-keys, esnext.reflect.get-own-metadata, esnext.reflect.get-own-metadata-keys, esnext.reflect.has-metadata, esnext.reflect.has-own-metadata and esnext.reflect.metadata.

namespace Reflect {
  defineMetadata(metadataKey: any, metadataValue: any, target: Object, propertyKey?: PropertyKey): void;
  getMetadata(metadataKey: any, target: Object, propertyKey?: PropertyKey): any;
  getOwnMetadata(metadataKey: any, target: Object, propertyKey?: PropertyKey): any;
  hasMetadata(metadataKey: any, target: Object, propertyKey?: PropertyKey): boolean;
  hasOwnMetadata(metadataKey: any, target: Object, propertyKey?: PropertyKey): boolean;
  deleteMetadata(metadataKey: any, target: Object, propertyKey?: PropertyKey): boolean;
  getMetadataKeys(target: Object, propertyKey?: PropertyKey): Array<mixed>;
  getOwnMetadataKeys(target: Object, propertyKey?: PropertyKey): Array<mixed>;
  metadata(metadataKey: any, metadataValue: any): decorator(target: Object, targetKey?: PropertyKey) => void;
}

CommonJS entry points:

core-js/proposals/reflect-metadata
core-js(-pure)/full/reflect/define-metadata
core-js(-pure)/full/reflect/delete-metadata
core-js(-pure)/full/reflect/get-metadata
core-js(-pure)/full/reflect/get-metadata-keys
core-js(-pure)/full/reflect/get-own-metadata
core-js(-pure)/full/reflect/get-own-metadata-keys
core-js(-pure)/full/reflect/has-metadata
core-js(-pure)/full/reflect/has-own-metadata
core-js(-pure)/full/reflect/metadata

Examples:

let object = {};
Reflect.defineMetadata('foo', 'bar', object);
Reflect.ownKeys(object);               // => []
Reflect.getOwnMetadataKeys(object);    // => ['foo']
Reflect.getOwnMetadata('foo', object); // => 'bar'

Web standards

self

Spec, module web.self

getter self: GlobalThisValue;

CommonJS entry points:

core-js(-pure)/stable|actual|full/self

Examples:

// eslint-disable-next-line no-restricted-globals -- example
self.Array === Array; // => true

structuredClone

Spec, module web.structured-clone

function structuredClone(value: Serializable, { transfer?: Sequence<Transferable> }): any;

CommonJS entry points:

core-js(-pure)/stable|actual|full/structured-clone

Examples:

const structured = [{ a: 42 }];
const sclone = structuredClone(structured);
console.log(sclone);                      // => [{ a: 42 }]
console.log(structured !== sclone);       // => true
console.log(structured[0] !== sclone[0]); // => true

const circular = {};
circular.circular = circular;
const cclone = structuredClone(circular);
console.log(cclone.circular === cclone);  // => true

structuredClone(42);                                            // => 42
structuredClone({ x: 42 });                                     // => { x: 42 }
structuredClone([1, 2, 3]);                                     // => [1, 2, 3]
structuredClone(new Set([1, 2, 3]));                            // => Set{ 1, 2, 3 }
structuredClone(new Map([['a', 1], ['b', 2]]));                 // => Map{ a: 1, b: 2 }
structuredClone(new Int8Array([1, 2, 3]));                      // => new Int8Array([1, 2, 3])
structuredClone(new AggregateError([1, 2, 3], 'message'));      // => new AggregateError([1, 2, 3], 'message'))
structuredClone(new TypeError('message', { cause: 42 }));       // => new TypeError('message', { cause: 42 })
structuredClone(new DOMException('message', 'DataCloneError')); // => new DOMException('message', 'DataCloneError')
structuredClone(document.getElementById('myfileinput'));        // => new FileList
structuredClone(new DOMPoint(1, 2, 3, 4));                      // => new DOMPoint(1, 2, 3, 4)
structuredClone(new Blob(['test']));                            // => new Blob(['test'])
structuredClone(new ImageData(8, 8));                           // => new ImageData(8, 8)
// etc.

structuredClone(new WeakMap()); // => DataCloneError on non-serializable types

[!WARNING]

Base64 utility methods

Specification, MDN. Modules web.atob, web.btoa.

function atob(data: string): string;
function btoa(data: string): string;

CommonJS entry points:

core-js(-pure)/stable|actual|full/atob
core-js(-pure)/stable|actual|full/btoa

Examples:

btoa('hi, core-js');      // => 'aGksIGNvcmUtanM='
atob('aGksIGNvcmUtanM='); // => 'hi, core-js'

setTimeout and setInterval

Module web.timers. Additional arguments fix for IE9-.

function setTimeout(callback: any, time: any, ...args: Array<mixed>): number;
function setInterval(callback: any, time: any, ...args: Array<mixed>): number;

CommonJS entry points:

core-js(-pure)/stable|actual|full/set-timeout
core-js(-pure)/stable|actual|full/set-interval
// Before:
setTimeout(log.bind(null, 42), 1000);
// After:
setTimeout(log, 1000, 42);

setImmediate

Module web.immediate. setImmediate polyfill.

function setImmediate(callback: any, ...args: Array<mixed>): number;
function clearImmediate(id: number): void;

CommonJS entry points:

core-js(-pure)/stable|actual|full/set-immediate
core-js(-pure)/stable|actual|full/clear-immediate

Examples:

setImmediate((arg1, arg2) => {
  console.log(arg1, arg2); // => Message will be displayed with minimum delay
}, 'Message will be displayed', 'with minimum delay');

clearImmediate(setImmediate(() => {
  console.log('Message will not be displayed');
}));

queueMicrotask

Spec, module web.queue-microtask

function queueMicrotask(fn: Function): void;

CommonJS entry points:

core-js(-pure)/stable|actual|full/queue-microtask

Examples:

queueMicrotask(() => console.log('called as microtask'));

URL and URLSearchParams

URL standard implementation. Modules web.url, web.url.can-parse, web.url.parse, web.url.to-json, web.url-search-params, web.url-search-params.delete, web.url-search-params.has, web.url-search-params.size.

class URL {
  constructor(url: string, base?: string);
  attribute href: string;
  readonly attribute origin: string;
  attribute protocol: string;
  attribute username: string;
  attribute password: string;
  attribute host: string;
  attribute hostname: string;
  attribute port: string;
  attribute pathname: string;
  attribute search: string;
  readonly attribute searchParams: URLSearchParams;
  attribute hash: string;
  toJSON(): string;
  toString(): string;
  static canParse(url: string, base?: string): boolean;
  static parse(url: string, base?: string): URL | null;
}

class URLSearchParams {
  constructor(params?: string | Iterable<[key, value]> | Object);
  append(name: string, value: string): void;
  delete(name: string, value?: string): void;
  get(name: string): string | void;
  getAll(name: string): Array<string>;
  has(name: string, value?: string): boolean;
  set(name: string, value: string): void;
  sort(): void;
  toString(): string;
  forEach(callbackfn: (value: any, index: number, target: any) => void, thisArg: any): void;
  entries(): Iterator<[key, value]>;
  keys(): Iterator<key>;
  values(): Iterator<value>;
  @@iterator(): Iterator<[key, value]>;
  readonly attribute size: number;
}

CommonJS entry points:

core-js/proposals/url
core-js(-pure)/stable|actual|full/url
core-js(-pure)/stable|actual|full/url/can-parse
core-js/stable|actual|full/url/to-json
core-js(-pure)/stable|actual|full/url-search-params

Examples:

URL.canParse('https://login:password@example.com:8080/?a=1&b=2&a=3&c=4#fragment'); // => true
URL.canParse('https'); // => false

URL.parse('https://login:password@example.com:8080/?a=1&b=2&a=3&c=4#fragment'); // => url
URL.parse('https'); // => null

const url = new URL('https://login:password@example.com:8080/foo/bar?a=1&b=2&a=3#fragment');

console.log(url.href);       // => 'https://login:password@example.com:8080/foo/bar?a=1&b=2&a=3#fragment'
console.log(url.origin);     // => 'https://example.com:8080'
console.log(url.protocol);   // => 'https:'
console.log(url.username);   // => 'login'
console.log(url.password);   // => 'password'
console.log(url.host);       // => 'example.com:8080'
console.log(url.hostname);   // => 'example.com'
console.log(url.port);       // => '8080'
console.log(url.pathname);   // => '/foo/bar'
console.log(url.search);     // => '?a=1&b=2&a=3'
console.log(url.hash);       // => '#fragment'
console.log(url.toJSON());   // => 'https://login:password@example.com:8080/foo/bar?a=1&b=2&a=3#fragment'
console.log(url.toString()); // => 'https://login:password@example.com:8080/foo/bar?a=1&b=2&a=3#fragment'

for (let [key, value] of url.searchParams) {
  console.log(key);   // => 'a', 'b', 'a'
  console.log(value); // => '1', '2', '3'
}

url.pathname = '';
url.searchParams.append('c', 4);

console.log(url.search); // => '?a=1&b=2&a=3&c=4'
console.log(url.href);   // => 'https://login:password@example.com:8080/?a=1&b=2&a=3&c=4#fragment'

const params = new URLSearchParams('?a=1&b=2&a=3');

params.append('c', 4);
params.append('a', 2);
params.delete('a', 1);
params.sort();

console.log(params.size); // => 4

for (let [key, value] of params) {
  console.log(key);   // => 'a', 'a', 'b', 'c'
  console.log(value); // => '3', '2', '2', '4'
}

console.log(params.has('a')); // => true
console.log(params.has('a', 3)); // => true
console.log(params.has('a', 4)); // => false

console.log(params.toString()); // => 'a=3&a=2&b=2&c=4'

[!WARNING]

DOMException:

The specification. Modules web.dom-exception.constructor, web.dom-exception.stack, web.dom-exception.to-string-tag.

class DOMException {
  constructor(message: string, name?: string);
  readonly attribute name: string;
  readonly attribute message: string;
  readonly attribute code: string;
  attribute stack: string; // in engines that should have it
  @@toStringTag: 'DOMException';
}

CommonJS entry points:

core-js(-pure)/stable|actual|full/dom-exception
core-js(-pure)/stable|actual|full/dom-exception/constructor
core-js/stable|actual|full/dom-exception/to-string-tag

Examples:

const exception = new DOMException('error', 'DataCloneError');
console.log(exception.name);                            // => 'DataCloneError'
console.log(exception.message);                         // => 'error'
console.log(exception.code);                            // => 25
console.log(typeof exception.stack);                    // => 'string'
console.log(exception instanceof DOMException);         // => true
console.log(exception instanceof Error);                // => true
console.log(exception.toString());                      // => 'DataCloneError: error'
console.log(Object.prototype.toString.call(exception)); // => '[object DOMException]'

Iterable DOM collections

Some DOM collections should have iterable interface or should be inherited from Array. That means they should have forEach, keys, values, entries and @@iterator methods for iteration. So add them. Modules web.dom-collections.iterator and web.dom-collections.for-each.

class [
  CSSRuleList,
  CSSStyleDeclaration,
  CSSValueList,
  ClientRectList,
  DOMRectList,
  DOMStringList,
  DataTransferItemList,
  FileList,
  HTMLAllCollection,
  HTMLCollection,
  HTMLFormElement,
  HTMLSelectElement,
  MediaList,
  MimeTypeArray,
  NamedNodeMap,
  PaintRequestList,
  Plugin,
  PluginArray,
  SVGLengthList,
  SVGNumberList,
  SVGPathSegList,
  SVGPointList,
  SVGStringList,
  SVGTransformList,
  SourceBufferList,
  StyleSheetList,
  TextTrackCueList,
  TextTrackList,
  TouchList,
] {
  @@iterator(): Iterator<value>;
}

class [DOMTokenList, NodeList] {
  forEach(callbackfn: (value: any, index: number, target: any) => void, thisArg: any): void;
  entries(): Iterator<[key, value]>;
  keys(): Iterator<key>;
  values(): Iterator<value>;
  @@iterator(): Iterator<value>;
}

CommonJS entry points:

core-js(-pure)/stable|actual|full/dom-collections/iterator
core-js/stable|actual|full/dom-collections/for-each

Examples:

for (let { id } of document.querySelectorAll('*')) {
  if (id) console.log(id);
}

for (let [index, { id }] of document.querySelectorAll('*').entries()) {
  if (id) console.log(index, id);
}

document.querySelectorAll('*').forEach(it => console.log(it.id));

Iteration helpers

Helpers for checking iterability / get iterator in the pure version or, for example, for arguments object:

function isIterable(value: any): boolean;
function getIterator(value: any): Object;
function getIteratorMethod(value: any): Function | void;

CommonJS entry points:

core-js-pure/es|stable|actual|full/is-iterable
core-js-pure/es|stable|actual|full/get-iterator
core-js-pure/es|stable|actual|full/get-iterator-method

Examples:

import isIterable from 'core-js-pure/actual/is-iterable';
import getIterator from 'core-js-pure/actual/get-iterator';
import getIteratorMethod from 'core-js-pure/actual/get-iterator-method';

let list = (function () {
  // eslint-disable-next-line prefer-rest-params -- example
  return arguments;
})(1, 2, 3);

console.log(isIterable(list)); // true;

let iterator = getIterator(list);
console.log(iterator.next().value); // 1
console.log(iterator.next().value); // 2
console.log(iterator.next().value); // 3
console.log(iterator.next().value); // undefined

getIterator({}); // TypeError: [object Object] is not iterable!

let method = getIteratorMethod(list);
console.log(typeof method);         // 'function'
iterator = method.call(list);
console.log(iterator.next().value); // 1
console.log(iterator.next().value); // 2
console.log(iterator.next().value); // 3
console.log(iterator.next().value); // undefined

console.log(getIteratorMethod({})); // undefined

Missing polyfills