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zloirock
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Description

Standard Library

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core-js

Sponsors on Open Collective Backers on Open Collective Gitter version npm downloads tests eslint

Modular standard library for JavaScript. Includes polyfills for ECMAScript up to 2021: 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 looking documentation for obsolete

[email protected]
, please, check this branch.

As advertising: the author is looking for a good job -)

[email protected], 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 on Open Collective or on Patreon if you are interested in
core-js
.



For enterprise

Available as part of the Tidelift Subscription.

The maintainers of

core-js
and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.

Example of usage: ```js import 'core-js'; // <- at the top of your entry point

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

You can load only required features: ```js import 'core-js/features/array/from'; // <- at the top of your entry point import 'core-js/features/array/flat'; // <- at the top of your entry point import 'core-js/features/set'; // <- at the top of your entry point import 'core-js/features/promise'; // <- at the top of your entry point

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

Or use it without global namespace pollution: ```js import from from 'core-js-pure/features/array/from'; import flat from 'core-js-pure/features/array/flat'; import Set from 'core-js-pure/features/set'; import Promise from 'core-js-pure/features/promise';

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

Index

Usage

Installation:

// global version
npm install --save [email protected]
// version without global namespace pollution
npm install --save [email protected]
// bundled global version
npm install --save [email protected]

Already bundled version of

core-js
on CDN (minified version).

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 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:
import "core-js";
// polyfill only stable `core-js` 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 ES proposals: import "core-js/features/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/features/set"; import Set from "core-js-pure/stable/set"; import Set from "core-js-pure/es/set";

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

// polyfill reflect metadata proposal: import "core-js/proposals/reflect-metadata"; // polyfill all stage 2+ proposals: import "core-js/stage/2";

Caveats when using CommonJS API:
  • modules
    path is an internal API, does not inject all required dependencies and can be changed in minor or patch releases. Use it only for a custom build and/or if you know what are you doing.
  • If you use
    core-js
    with the extension of native objects, recommended load all
    core-js
    modules at the top of the entry point of your application, otherwise, you can have conflicts.
    • For example, Google Maps use their own
      Symbol.iterator
      , conflicting with
      Array.from
      ,
      URLSearchParams
      and/or something else from
      core-js
      , see related issues.
    • Such conflicts also resolvable by discrovering and manual adding each conflicting entry from
      core-js
      .
  • core-js
    is extremely modular and uses a lot of very tiny modules, because of that for usage in browsers bundle up
    core-js
    instead of usage loader for each file, otherwise, you will have hundreds of requests.

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: ```js import fill from 'core-js-pure/features/array/virtual/fill'; import findIndex from 'core-js-pure/features/array/virtual/find-index';

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

// or

import { fill, findIndex } from 'core-js-pure/features/array/virtual';

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

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 favour of separate inclusion of required parts of

core-js
and
regenerator-runtime
and, for preventing breaking changes, left on
[email protected]
.

As a full equal of

@babel/polyfill
, you can use this:
js
import 'core-js/stable';
import 'regenerator-runtime/runtime';

@babel/preset-env

@babel/preset-env
has

useBuiltIns
option, which optimizes working with global version of
core-js
. With
useBuiltIns
option, you should also set
corejs
option to used version of
core-js
, like
corejs: '3.8'
.

Warning! Recommended to specify used minor

core-js
version, like
corejs: '3.8'
, instead of
corejs: 3
, since with
corejs: 3
will not be injected modules which were added in minor
core-js
releases.
  • useBuiltIns: 'entry'
    replaces imports of
    core-js
    to import only required for a target environment modules. So, for example,
    js
    import 'core-js/stable';
    
    with
    chrome 71
    target will be replaced just to:
    js
    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
    js
    import 'core-js/es';
    import 'core-js/proposals/set-methods';
    import 'core-js/features/set/map';
    
    with
    chrome 71
    target you will have as a result:
    js
    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";
    
  • useBuiltIns: 'usage'
    adds to the top of each file import of polyfills for features used in this file and not supported by target environments, so for: ```js // first file: var set = new Set([1, 2, 3]);

// second file: var array = Array.of(1, 2, 3);

if target contains an old environment like `IE 11` we will have something like:
js // 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
proposals
option, as
corejs: { version: '3.8', proposals: true }
.

@babel/runtime

@babel/runtime
with

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

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
use 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 inverse problem - knowingly broken environment with problems not covered by

core-js
feature detection.

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

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

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

require('core-js');

It does not work with some features. Also, if you change the default behaviour, 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.

Compatibility data

core-js-compat
package contains data about the necessity of

core-js
modules and API for getting a list of required
core-js
modules by
browserslist
query.

Supported engines

Tested in: - Chrome 26+ - Firefox 4+ - Safari 5+ - Opera 12+ - Internet Explorer 8+ (sure, IE8 with ES3 limitations; IE7- also should work, but no longer tested) - Edge - Android Browser 2.3+ - iOS Safari 5.1+ - PhantomJS 1.9+ - NodeJS 0.8+

...and it doesn't mean

core-js
will not work in other engines, they just have not been tested.

Features:

CommonJS entry points:

core-js(-pure)

ECMAScript

CommonJS entry points:

core-js(-pure)/es

ECMAScript: Object

Modules

es.object.assign
,
es.object.is
,
es.object.set-prototype-of
,
es.object.to-string
,
es.object.freeze
,
es.object.seal
,
es.object.prevent-extensions
,
es.object.is-frozen
,
es.object.is-sealed
,
es.object.is-extensible
,
es.object.get-own-property-descriptor
,
es.object.get-own-property-descriptors
,
es.object.get-prototype-of
,
es.object.keys
,
es.object.values
,
es.object.entries
,
es.object.get-own-property-names
and
es.object.from-entries
.

Just ES5 features:

es.object.create
,
es.object.define-property
and
es.object.define-properties
.

ES2017 Annex B - modules

es.object.define-setter
,
es.object.define-getter
,
es.object.lookup-setter
and
es.object.lookup-getter

js
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;
  static assign(target: Object, ...sources: Array): 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;
  static freeze(object: any): any;
  static fromEntries(iterable: Iterable): Object;
  static getOwnPropertyDescriptor(object: any, property: PropertyKey): PropertyDescriptor | void;
  static getOwnPropertyDescriptors(object: any): { [property: PropertyKey]: PropertyDescriptor };
  static getOwnPropertyNames(object: any): Array;
  static getPrototypeOf(object: any): Object | null;
  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;
  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;
}
CommonJS entry points:
core-js(-pure)/es|stable|features/object
core-js(-pure)/es|stable|features/object/assign
core-js(-pure)/es|stable|features/object/is
core-js(-pure)/es|stable|features/object/set-prototype-of
core-js(-pure)/es|stable|features/object/get-prototype-of
core-js(-pure)/es|stable|features/object/create
core-js(-pure)/es|stable|features/object/define-property
core-js(-pure)/es|stable|features/object/define-properties
core-js(-pure)/es|stable|features/object/get-own-property-descriptor
core-js(-pure)/es|stable|features/object/get-own-property-descriptors
core-js(-pure)/es|stable|features/object/keys
core-js(-pure)/es|stable|features/object/values
core-js(-pure)/es|stable|features/object/entries
core-js(-pure)/es|stable|features/object/get-own-property-names
core-js(-pure)/es|stable|features/object/freeze
core-js(-pure)/es|stable|features/object/from-entries
core-js(-pure)/es|stable|features/object/seal
core-js(-pure)/es|stable|features/object/prevent-extensions
core-js(-pure)/es|stable|features/object/is-frozen
core-js(-pure)/es|stable|features/object/is-sealed
core-js(-pure)/es|stable|features/object/is-extensible
core-js/es|stable|features/object/to-string
core-js(-pure)/es|stable|features/object/define-getter
core-js(-pure)/es|stable|features/object/define-setter
core-js(-pure)/es|stable|features/object/lookup-getter
core-js(-pure)/es|stable|features/object/lookup-setter
Examples: ```js 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() {} function Child() {} Object.setPrototypeOf(Child.prototype, Parent.prototype); new Child() instanceof Child; // => true new Child() instanceof Parent; // => true

let object = { [Symbol.toStringTag]: 'Foo' };

'' + object; // => '[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 } } ```

ECMAScript: Function

Modules

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

js
class Function {
  name: string;
  bind(thisArg: any, ...args: Array): Function;
  @@hasInstance(value: any): boolean;
}
CommonJS entry points:
core-js/es|stable|features/function
core-js/es|stable|features/function/name
core-js/es|stable|features/function/has-instance
core-js/es|stable|features/function/bind
core-js/es|stable|features/function/virtual/bind
Example: ```js (function foo() {}).name // => 'foo'

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

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.iterator
,
es.array.includes
,
es.array.slice
,
es.array.join
,
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
and
es.array.unscopables.flat-map
```js class Array { concat(...args: Array): Array; // 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; // 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): number; flat(depthArg?: number = 1): Array; flatMap(mapFn: (value: any, index: number, target: any) => any, thisArg: any): Array; 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; lastIndexOf(searchElement: any, from?: number): number; map(mapFn: (value: any, index: number, target: any) => any, thisArg?: any): Array; // with adding support of @@species 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; // with adding support of @@species splice(start?: number, deleteCount?: number, ...items: Array): Array; // 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; values(): Iterator; @@iterator(): Iterator; @@unscopables: { [newMethodNames: string]: true }; static from(items: Iterable | ArrayLike, mapFn?: (value: any, index: number) => any, thisArg?: any): Array; static isArray(value: any): boolean; static of(...args: Array): Array; }

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

[*CommonJS entry points:*](#commonjs-api)
core-js(-pure)/es|stable|features/array core-js(-pure)/es|stable|features/array/from core-js(-pure)/es|stable|features/array/of core-js(-pure)/es|stable|features/array/is-array core-js(-pure)/es|stable|features/array/concat core-js(-pure)/es|stable|features/array/entries core-js(-pure)/es|stable|features/array/every core-js(-pure)/es|stable|features/array/copy-within core-js(-pure)/es|stable|features/array/fill core-js(-pure)/es|stable|features/array/filter core-js(-pure)/es|stable|features/array/find core-js(-pure)/es|stable|features/array/find-index core-js(-pure)/es|stable|features/array/flat core-js(-pure)/es|stable|features/array/flat-map core-js(-pure)/es|stable|features/array/for-each core-js(-pure)/es|stable|features/array/includes core-js(-pure)/es|stable|features/array/index-of core-js(-pure)/es|stable|features/array/iterator core-js(-pure)/es|stable|features/array/join core-js(-pure)/es|stable|features/array/keys core-js(-pure)/es|stable|features/array/last-index-of core-js(-pure)/es|stable|features/array/map core-js(-pure)/es|stable|features/array/reduce core-js(-pure)/es|stable|features/array/reduce-right core-js(-pure)/es|stable|features/array/reverse core-js(-pure)/es|stable|features/array/slice core-js(-pure)/es|stable|features/array/splice core-js(-pure)/es|stable|features/array/some core-js(-pure)/es|stable|features/array/sort core-js(-pure)/es|stable|features/array/values core-js(-pure)/es|stable|features/array/virtual/concat core-js(-pure)/es|stable|features/array/virtual/copy-within core-js(-pure)/es|stable|features/array/virtual/entries core-js(-pure)/es|stable|features/array/virtual/every core-js(-pure)/es|stable|features/array/virtual/fill core-js(-pure)/es|stable|features/array/virtual/filter core-js(-pure)/es|stable|features/array/virtual/find core-js(-pure)/es|stable|features/array/virtual/find-index core-js(-pure)/es|stable|features/array/virtual/flat core-js(-pure)/es|stable|features/array/virtual/flat-map core-js(-pure)/es|stable|features/array/virtual/for-each core-js(-pure)/es|stable|features/array/virtual/includes core-js(-pure)/es|stable|features/array/virtual/index-of core-js(-pure)/es|stable|features/array/virtual/iterator core-js(-pure)/es|stable|features/array/virtual/join core-js(-pure)/es|stable|features/array/virtual/keys core-js(-pure)/es|stable|features/array/virtual/last-index-of core-js(-pure)/es|stable|features/array/virtual/map core-js(-pure)/es|stable|features/array/virtual/reduce core-js(-pure)/es|stable|features/array/virtual/reduce-right core-js(-pure)/es|stable|features/array/virtual/reverse core-js(-pure)/es|stable|features/array/virtual/slice core-js(-pure)/es|stable|features/array/virtual/some core-js(-pure)/es|stable|features/array/virtual/sort core-js(-pure)/es|stable|features/array/virtual/splice core-js(-pure)/es|stable|features/array/virtual/values
[*Examples*](https://goo.gl/Tegvq4):
js 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 [4, 8, 15, 16, 23, 42].find(isNaN); // => undefined [4, 8, 15, 16, 23, 42].findIndex(isNaN); // => -1

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] ```

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
.

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 HTML methods. Ugly, but it's also the part of the spec. 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
and
es.string.sup
.

RegExp
features: modules
es.regexp.constructor
,
es.regexp.flags
,
es.regexp.sticky
and
es.regexp.test
. ```js class String { static fromCodePoint(...codePoints: Array): string; static raw({ raw: Array }, ...substitutions: Array): string; split(separator: string, limit?: number): Array; 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: any): any; // ES2015+ fix for support @@split, some fixes for old engines trim(): string; trimLeft(): string; trimRight(): string; trimStart(): string; trimEnd(): 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; sup(): string; @@iterator(): Iterator; }

class RegExp { constructor(pattern: RegExp | string, flags?: string): RegExp; // support of sticky (

y
) flag; can alter flags exec(): Array | null; // IE8 fixes test(string: string): boolean; // delegation to
.exec
toString(): string; // ES2015+ fix - generic @@match(string: string): Array | null; @@replace(string: string, replaceValue: Function | string): string; @@search(string: string): number; @@split(string: string, limit: number): Array; readonly attribute flags: string; // IE9+ readonly attribute sticky: boolean; }
[*CommonJS entry points:*](#commonjs-api)
core-js(-pure)/es|stable|features/string core-js(-pure)/es|stable|features/string/from-code-point core-js(-pure)/es|stable|features/string/raw core-js(-pure)/es|stable|features/string/code-point-at core-js(-pure)/es|stable|features/string/ends-with core-js(-pure)/es|stable|features/string/includes core-js(-pure)/es|stable|features/string/starts-with core-js/es|stable|features/string/match core-js(-pure)/es|stable|features/string/match-all core-js(-pure)/es|stable|features/string/pad-start core-js(-pure)/es|stable|features/string/pad-end core-js(-pure)/es|stable|features/string/repeat core-js/es|stable|features/string/replace core-js(-pure)/es|stable|features/string/replace-all core-js/es|stable|features/string/search core-js/es|stable|features/string/split core-js(-pure)/es|stable|features/string/trim core-js(-pure)/es|stable|features/string/trim-start core-js(-pure)/es|stable|features/string/trim-end core-js(-pure)/es|stable|features/string/trim-left core-js(-pure)/es|stable|features/string/trim-right core-js(-pure)/es|stable|features/string/anchor core-js(-pure)/es|stable|features/string/big core-js(-pure)/es|stable|features/string/blink core-js(-pure)/es|stable|features/string/bold core-js(-pure)/es|stable|features/string/fixed core-js(-pure)/es|stable|features/string/fontcolor core-js(-pure)/es|stable|features/string/fontsize core-js(-pure)/es|stable|features/string/italics core-js(-pure)/es|stable|features/string/link core-js(-pure)/es|stable|features/string/small core-js(-pure)/es|stable|features/string/strike core-js(-pure)/es|stable|features/string/sub core-js(-pure)/es|stable|features/string/sup core-js(-pure)/es|stable|features/string/iterator core-js(-pure)/es|stable|features/string/virtual/includes core-js(-pure)/es|stable|features/string/virtual/starts-with core-js(-pure)/es|stable|features/string/virtual/ends-with core-js(-pure)/es|stable|features/string/virtual/match-all core-js(-pure)/es|stable|features/string/virtual/repeat core-js(-pure)/es|stable|features/string/virtual/replace-all core-js(-pure)/es|stable|features/string/virtual/pad-start core-js(-pure)/es|stable|features/string/virtual/pad-end core-js(-pure)/es|stable|features/string/virtual/code-point-at core-js(-pure)/es|stable|features/string/virtual/trim core-js(-pure)/es|stable|features/string/virtual/trim-start core-js(-pure)/es|stable|features/string/virtual/trim-end core-js(-pure)/es|stable|features/string/virtual/trim-left core-js(-pure)/es|stable|features/string/virtual/trim-right core-js(-pure)/es|stable|features/string/virtual/anchor core-js(-pure)/es|stable|features/string/virtual/big core-js(-pure)/es|stable|features/string/virtual/blink core-js(-pure)/es|stable|features/string/virtual/bold core-js(-pure)/es|stable|features/string/virtual/fixed core-js(-pure)/es|stable|features/string/virtual/fontcolor core-js(-pure)/es|stable|features/string/virtual/fontsize core-js(-pure)/es|stable|features/string/virtual/italics core-js(-pure)/es|stable|features/string/virtual/link core-js(-pure)/es|stable|features/string/virtual/small core-js(-pure)/es|stable|features/string/virtual/strike core-js(-pure)/es|stable|features/string/virtual/sub core-js(-pure)/es|stable|features/string/virtual/sup core-js(-pure)/es|stable|features/string/virtual/iterator core-js/es|stable|features/regexp core-js/es|stable|features/regexp/constructor core-js(-pure)/es|stable|features/regexp/flags core-js/es|stable|features/regexp/sticky core-js/es|stable|features/regexp/test core-js/es|stable|features/regexp/to-string
[*Examples*](http://es6.zloirock.ru/#for(var%20val%20of%20'a%F0%A0%AE%B7b')%7B%0A%20%20log(val)%3B%20%2F%2F%20%3D%3E%20'a'%2C%20'%F0%A0%AE%B7'%2C%20'b'%0A%7D%0A%0Alog('foobarbaz'.includes('bar'))%3B%20%20%20%20%20%20%2F%2F%20%3D%3E%20true%0Alog('foobarbaz'.includes('bar'%2C%204))%3B%20%20%20%2F%2F%20%3D%3E%20false%0Alog('foobarbaz'.startsWith('foo'))%3B%20%20%20%20%2F%2F%20%3D%3E%20true%0Alog('foobarbaz'.startsWith('bar'%2C%203))%3B%20%2F%2F%20%3D%3E%20true%0Alog('foobarbaz'.endsWith('baz'))%3B%20%20%20%20%20%20%2F%2F%20%3D%3E%20true%0Alog('foobarbaz'.endsWith('bar'%2C%206))%3B%20%20%20%2F%2F%20%3D%3E%20true%0A%0Alog('string'.repeat(3))%3B%20%2F%2F%20%3D%3E%20'stringstringstring'%0A%0Alog('hello'.padStart(10))%3B%20%20%20%20%20%20%20%20%20%2F%2F%20%3D%3E%20'%20%20%20%20%20hello'%0Alog('hello'.padStart(10%2C%20'1234'))%3B%20%2F%2F%20%3D%3E%20'12341hello'%0Alog('hello'.padEnd(10))%3B%20%20%20%20%20%20%20%20%20%20%20%2F%2F%20%3D%3E%20'hello%20%20%20%20%20'%0Alog('hello'.padEnd(10%2C%20'1234'))%3B%20%20%20%2F%2F%20%3D%3E%20'hello12341'%0A%0Alog('%F0%A0%AE%B7'.codePointAt(0))%3B%20%2F%2F%20%3D%3E%20134071%0A%0Avar%20name%20%3D%20'Bob'%3B%0Alog(String.raw%60Hi%5Cn%24%7Bname%7D!%60)%3B%20%20%20%20%20%20%20%20%20%20%20%20%20%2F%2F%20%3D%3E%20'Hi%5C%5CnBob!'%20(ES6%20template%20string%20syntax)%0Alog(String.raw(%7B%20raw%3A%20'test'%20%7D%2C%200%2C%201%2C%202))%3B%20%2F%2F%20%3D%3E%20%2F%2F%20't0e1s2t'%0A%0Alog('foo'.bold())%3B%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%2F%2F%20%3D%3E%20'%3Cb%3Efoo%3C%2Fb%3E'%0Alog('bar'.anchor('a%22b'))%3B%20%20%20%20%20%20%20%20%20%20%20%20%20%20%2F%2F%20%3D%3E%20'%3Ca%20name%3D%22a%26quot%3Bb%22%3Ebar%3C%2Fa%3E'%0Alog('baz'.link('http%3A%2F%2Fexample.com'))%3B%20%2F%2F%20%3D%3E%20'%3Ca%20href%3D%22http%3A%2F%2Fexample.com%22%3Ebaz%3C%2Fa%3E'%0A%0Alog(RegExp(%2F.%2Fg%2C%20'm'))%3B%20%2F%2F%20%3D%3E%20%2F.%2Fm%0A%0Alog(%2Ffoo%2F.flags)%3B%20%20%20%20%2F%2F%20%3D%3E%20''%0Alog(%2Ffoo%2Fgim.flags)%3B%20%2F%2F%20%3D%3E%20'gim'%0A%0Alog(RegExp('foo'%2C%20'y').sticky)%3B%20%2F%2F%20%3D%3E%20true%0A%0Aconst%20text%20%3D%20'First%20line%5CnSecond%20line'%3B%0Aconst%20regex%20%3D%20RegExp('(%5C%5CS%2B)%20line%5C%5Cn%3F'%2C%20'y')%3B%0A%0Alog(regex.exec(text)%5B1%5D)%3B%20%2F%2F%20%3D%3E%20'First'%0Alog(regex.exec(text)%5B1%5D)%3B%20%2F%2F%20%3D%3E%20'Second'%0Alog(regex.exec(text))%3B%20%20%20%20%2F%2F%20%3D%3E%20null%0A%0Alog('foo'.match(%7B%5BSymbol.match%5D%3A%20_%20%3D%3E%201%7D))%3B%20%20%20%20%20%2F%2F%20%3D%3E%201%0Alog('foo'.replace(%7B%5BSymbol.replace%5D%3A%20_%20%3D%3E%202%7D))%3B%20%2F%2F%20%3D%3E%202%0Alog('foo'.search(%7B%5BSymbol.search%5D%3A%20_%20%3D%3E%203%7D))%3B%20%20%20%2F%2F%20%3D%3E%203%0Alog('foo'.split(%7B%5BSymbol.split%5D%3A%20_%20%3D%3E%204%7D))%3B%20%20%20%20%20%2F%2F%20%3D%3E%204%0A%0Alog(RegExp.prototype.toString.call(%7Bsource%3A%20'foo'%2C%20flags%3A%20'bar'%7D))%3B%0A%0Alog('%20%20%20hello%20%20%20'.trimLeft())%3B%20%20%2F%2F%20%3D%3E%20'hello%20%20%20'%0Alog('%20%20%20hello%20%20%20'.trimRight())%3B%20%2F%2F%20%3D%3E%20'%20%20%20hello'%0Alog('%20%20%20hello%20%20%20'.trimStart())%3B%20%2F%2F%20%3D%3E%20'hello%20%20%20'%0Alog('%20%20%20hello%20%20%20'.trimEnd())%3B%20%20%20%2F%2F%20%3D%3E%20'%20%20%20hello'%0A%0Afor%20(let%20%5B_%2C%20d%2C%20D%5D%20of%20'1111a2b3cccc'.matchAll(%2F(%5Cd)(%5CD)%2Fg))%20%7B%0A%20%20log(d%2C%20D)%3B%20%2F%2F%20%3D%3E%201%20a%2C%202%20b%2C%203%20c%0A%7D%0A%0Alog('Test%20abc%20test%20test%20abc%20test.'.replaceAll('abc'%2C%20'foo'))%3B%20%2F%2F%20-%3E%20'Test%20foo%20test%20test%20foo%20test.'):
js 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(); // => 'foo' 'bar'.anchor('a"b'); // => 'bar' 'baz'.link('http://example.com'); // => 'baz'

RegExp(/./g, 'm'); // => /./m

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

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

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

regex.exec(text)[1]; // => 'First' regex.exec(text)[1]; // => '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 [_, d, D] of '1111a2b3cccc'.matchAll(/(\d)(\D)/g)) { console.log(d, D); // => 1 a, 2 b, 3 c }

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

ECMAScript: Number

Module

es.number.constructor
.

Number
constructor support binary and octal literals, example:
js
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-fixed
,
es.number.to-precision
,
es.parse-int
,
es.parse-float
. ```js class Number { constructor(value: any): number; 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 MAXSAFEINTEGER: number; static MINSAFEINTEGER: number; }

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

[*CommonJS entry points:*](#commonjs-api)
core-js(-pure)/es|stable|features/number core-js/es|stable|features/number/constructor core-js(-pure)/es|stable|features/number/is-finite core-js(-pure)/es|stable|features/number/is-nan core-js(-pure)/es|stable|features/number/is-integer core-js(-pure)/es|stable|features/number/is-safe-integer core-js(-pure)/es|stable|features/number/parse-float core-js(-pure)/es|stable|features/number/parse-int core-js(-pure)/es|stable|features/number/epsilon core-js(-pure)/es|stable|features/number/max-safe-integer core-js(-pure)/es|stable|features/number/min-safe-integer core-js(-pure)/es|stable|features/number/to-fixed core-js(-pure)/es|stable|features/number/to-precision core-js(-pure)/es|stable|features/parse-float core-js(-pure)/es|stable|features/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
.

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

js
class Date {
  toISOString(): string;
  toJSON(): string;
  toString(): string;
  @@toPrimitive(hint: 'default' | 'number' | 'string'): string | number;
  static now(): number;
}
CommonJS entry points:
core-js/es|stable|features/date
core-js/es|stable|features/date/to-string
core-js(-pure)/es|stable|features/date/now
core-js(-pure)/es|stable|features/date/to-iso-string
core-js(-pure)/es|stable|features/date/to-json
core-js(-pure)/es|stable|features/date/to-primitive
Example:
js
new Date(NaN).toString(); // => 'Invalid Date'

ECMAScript: Promise

Modules

es.aggregate-error
,
es.promise
,
es.promise.all-settled
,
es.promise.any
and
es.promise.finally
. ```js class AggregateError { constructor(errors: Iterable, message: string): AggregateError; errors: Array; message: string; }

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 resolve(x: any): Promise; static reject(r: any): Promise; static all(iterable: Iterable): Promise; static allSettled(iterable: Iterable): Promise; static any(promises: Iterable): Promise; static race(iterable: Iterable): Promise; }

[*CommonJS entry points:*](#commonjs-api)
core-js(-pure)/es|stable|features/aggregate-error core-js(-pure)/es|stable|features/promise core-js(-pure)/es|stable|features/promise/all-settled core-js(-pure)/es|stable|features/promise/any core-js(-pure)/es|stable|features/promise/finally
Basic [*example*](http://goo.gl/vGrtUC):
js 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 Error('Irror!'); }).then(() => { console.log('will not be displayed'); }).catch(x => console.log(x)); // => => Error: Irror!

`Promise.resolve` and `Promise.reject` [*example*](http://goo.gl/vr8TN3):
js Promise.resolve(42).then(x => console.log(x)); // => 42 Promise.reject(42).catch(x => console.log(x)); // => 42

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

`Promise#finally` [*example*](https://goo.gl/AhyBbJ):
js 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*](http://goo.gl/RdoDBZ):
js Promise.all([ 'foo', sleepRandom(5), sleepRandom(15), sleepRandom(10) // after 15 sec: ]).then(x => console.log(x)); // => ['foo', 956, 85, 382]
`Promise.race` [*example*](http://goo.gl/L8ovkJ):
js function timeLimit(promise, time) { return Promise.race([promise, new Promise((resolve, reject) => { setTimeout(reject, time * 1e3, Error('Await > ' + time + ' sec')); })]); }

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

`Promise.allSettled` [*example*](https://goo.gl/PXXLNJ):
js 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*](https://goo.gl/iErvmp):
js 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]

[Example](http://goo.gl/wnQS4j) with async functions:
js 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 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 (e) { console.log(e); // => Error: 'Error!', after 5 sec. } })(); ```

Unhandled rejection tracking

In Node.js, like in native implementation, available events

unhandledRejection
and
rejectionHandled
: ```js 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]

setTimeout(() => promise.catch(() => {}), 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*](http://goo.gl/Wozskl):
js window.addEventListener('unhandledrejection', e => console.log('unhandled', e.reason, e.promise)); window.addEventListener('rejectionhandled', e => console.log('handled', e.reason, e.promise)); // or window.onunhandledrejection = e => console.log('unhandled', e.reason, e.promise); window.onrejectionhandled = e => console.log('handled', e.reason, e.promise);

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

setTimeout(() => promise.catch(() => {}), 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
. ```js 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; }

Also wrapped some methods for correct work with `Symbol` polyfill.
js 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; propertyIsEnumerable(key: PropertyKey): boolean; }
[*CommonJS entry points:*](#commonjs-api)
core-js(-pure)/es|stable|features/symbol core-js(-pure)/es|stable|features/symbol/async-iterator core-js/es|stable|features/symbol/description core-js(-pure)/es|stable|features/symbol/has-instance core-js(-pure)/es|stable|features/symbol/is-concat-spreadable core-js(-pure)/es|stable|features/symbol/iterator core-js(-pure)/es|stable|features/symbol/match core-js(-pure)/es|stable|features/symbol/replace core-js(-pure)/es|stable|features/symbol/search core-js(-pure)/es|stable|features/symbol/species core-js(-pure)/es|stable|features/symbol/split core-js(-pure)/es|stable|features/symbol/to-primitive core-js(-pure)/es|stable|features/symbol/to-string-tag core-js(-pure)/es|stable|features/symbol/unscopables core-js(-pure)/es|stable|features/symbol/for core-js(-pure)/es|stable|features/symbol/key-for core-js(-pure)/es|stable|features/object/get-own-property-symbols core-js(-pure)/es|stable|features/math/to-string-tag
[*Basic example*](http://goo.gl/BbvWFc):
js 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*](http://goo.gl/0pdJjX):
js let symbol = Symbol.for('key'); symbol === Symbol.for('key'); // true Symbol.keyFor(symbol); // 'key'
[*Example*](http://goo.gl/mKVOQJ) with methods for getting own object keys:
js 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:

js
Symbol('foo').description; // => 'foo'
Symbol().description;      // => undefined
Caveats when using
Symbol
polyfill:
  • We can't add new primitive type,
    Symbol
    returns object.
  • Symbol.for
    and
    Symbol.keyFor
    can't be shimmed cross-realm.
  • By default, to hide the keys,
    Symbol
    polyfill defines setter in
    Object.prototype
    . For this reason, uncontrolled creation of symbols can cause memory leak and the
    in
    operator is not working correctly with
    Symbol
    polyfill:
    Symbol() in {} // => true
    .

You can disable defining setters in

Object.prototype
. Example: ```js 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 ``

* Currently,
core-js
not adds setters to
Object.prototype
for well-known symbols for correct work something like
Symbol.iterator in foo
. It can cause problems with their enumerability.
* Some problems possible with environment exotic objects (for example, IE
localStorage`).

ECMAScript: Collections

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

Map

Module

es.map
.

js
class Map {
  constructor(iterable?: Iterable): 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;
  keys(): Iterator;
  entries(): Iterator;
  @@iterator(): Iterator;
  readonly attribute size: number;
}
CommonJS entry points:
core-js(-pure)/es|stable|features/map
Examples: ```js 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]]

let 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 } ```

Set

Module

es.set
.

js
class Set {
  constructor(iterable?: Iterable): 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;
  keys(): Iterator;
  entries(): Iterator;
  @@iterator(): Iterator;
  readonly attribute size: number;
}
CommonJS entry points:
core-js(-pure)/es|stable|features/set
Examples: ```js 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']

let 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 } ```

WeakMap

Module

es.weak-map
.

js
class WeakMap {
  constructor(iterable?: Iterable): 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|features/weak-map
Examples: ```js 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
.

js
class WeakSet {
  constructor(iterable?: Iterable): WeakSet;
  add(key: Object): this;
  delete(key: Object): boolean;
  has(key: Object): boolean;
}
CommonJS entry points:
core-js(-pure)/es|stable|features/weak-set
Examples: ```js 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 ```

Caveats when using collections polyfill:
  • Weak-collections polyfill stores values as hidden properties of keys. It works correct and not leak in most cases. However, it is desirable to store a collection longer than its keys.

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
,
es.array-buffer.slice
,
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.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
and
es.typed-array.to-string
. ```js class ArrayBuffer { constructor(length: any): ArrayBuffer; slice(start: any, end: any): ArrayBuffer; readonly attribute byteLength: number; 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, ] { constructor(length: number): %TypedArray%; constructor(object: %TypedArray% | Iterable | ArrayLike): %TypedArray%; constructor(buffer: ArrayBuffer, byteOffset?: number, length?: number): %TypedArray%; copyWithin(target: number, start: number, end?: number): this; 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): number; 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; 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; subarray(begin?: number, end?: number): %TypedArray%; toString(): string; toLocaleString(): string; values(): Iterator; keys(): Iterator; entries(): Iterator<[index, value]>; @@iterator(): Iterator; readonly attribute buffer: ArrayBuffer; readonly attribute byteLength: number; readonly attribute byteOffset: number; readonly attribute length: number; BYTESPERELEMENT: number; static from(items: Iterable | ArrayLike, mapFn?: (value: any, index: number) => any, thisArg?: any): %TypedArray%; static of(...args: Array): %TypedArray%; static BYTESPERELEMENT: number; }

[*CommonJS entry points:*](#commonjs-api)
core-js/es|stable|features/array-buffer core-js/es|stable|features/array-buffer/constructor core-js/es|stable|features/array-buffer/is-view core-js/es|stable|features/array-buffer/slice core-js/es|stable|features/data-view core-js/es|stable|features/typed-array core-js/es|stable|features/typed-array/int8-array core-js/es|stable|features/typed-array/uint8-array core-js/es|stable|features/typed-array/uint8-clamped-array core-js/es|stable|features/typed-array/int16-array core-js/es|stable|features/typed-array/uint16-array core-js/es|stable|features/typed-array/int32-array core-js/es|stable|features/typed-array/uint32-array core-js/es|stable|features/typed-array/float32-array core-js/es|stable|features/typed-array/float64-array core-js/es|stable|features/typed-array/copy-within core-js/es|stable|features/typed-array/entries core-js/es|stable|features/typed-array/every core-js/es|stable|features/typed-array/fill core-js/es|stable|features/typed-array/filter core-js/es|stable|features/typed-array/find core-js/es|stable|features/typed-array/find-index core-js/es|stable|features/typed-array/for-each core-js/es|stable|features/typed-array/from core-js/es|stable|features/typed-array/includes core-js/es|stable|features/typed-array/index-of core-js/es|stable|features/typed-array/iterator core-js/es|stable|features/typed-array/join core-js/es|stable|features/typed-array/keys core-js/es|stable|features/typed-array/last-index-of core-js/es|stable|features/typed-array/map core-js/es|stable|features/typed-array/of core-js/es|stable|features/typed-array/reduce core-js/es|stable|features/typed-array/reduce-right core-js/es|stable|features/typed-array/reverse core-js/es|stable|features/typed-array/set core-js/es|stable|features/typed-array/slice core-js/es|stable|features/typed-array/some core-js/es|stable|features/typed-array/sort core-js/es|stable|features/typed-array/subarray core-js/es|stable|features/typed-array/to-locale-string core-js/es|stable|features/typed-array/to-string core-js/es|stable|features/typed-array/values
[*Examples*](http://goo.gl/yla75z):
js 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 } ```

Caveats when using typed arrays polyfills:
  • Polyfills of Typed Arrays constructors work completely how should work by the spec, but because of internal usage of getters / setters on each instance, are slow and consumes significant memory. However, polyfills of Typed Arrays constructors required mainly for old IE, all modern engines have native Typed Arrays constructors and require only fixes of constructors and polyfills of methods.

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
.

js
namespace Reflect {
  apply(target: Function, thisArgument: any, argumentsList: Array): any;
  construct(target: Function, argumentsList: Array, 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;
  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|features/reflect
core-js(-pure)/es|stable|features/reflect/apply
core-js(-pure)/es|stable|features/reflect/construct
core-js(-pure)/es|stable|features/reflect/define-property
core-js(-pure)/es|stable|features/reflect/delete-property
core-js(-pure)/es|stable|features/reflect/get
core-js(-pure)/es|stable|features/reflect/get-own-property-descriptor
core-js(-pure)/es|stable|features/reflect/get-prototype-of
core-js(-pure)/es|stable|features/reflect/has
core-js(-pure)/es|stable|features/reflect/is-extensible
core-js(-pure)/es|stable|features/reflect/own-keys
core-js(-pure)/es|stable|features/reflect/prevent-extensions
core-js(-pure)/es|stable|features/reflect/set
core-js(-pure)/es|stable|features/reflect/set-prototype-of
Examples: ```js 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
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
.

js
namespace JSON {
  stringify(target: any, replacer?: Function | Array, space?: string | number): string | void;
  @@toStringTag: 'JSON';
}
CommonJS entry points:
js
core-js(-pure)/es|stable|features/json/stringify
core-js(-pure)/es|stable|features/json/to-string-tag
Examples:
js
JSON.stringify({ '𠮷': ['\uDF06\uD834'] }); // => '{"𠮷":["\\udf06\\ud834"]}'

ECMAScript: globalThis

Module

es.global-this
.

js
let globalThis: Object;
CommonJS entry points:
js
core-js(-pure)/es|stable|features/global-this
Examples:
js
globalThis.Array === Array; // => true

ECMAScript proposals

The TC39 process.

core-js/stage/4
entry point contains only stage 4 proposals,
core-js/stage/3
- stage 3 and stage 4, etc.

Stage 4 proposals

Stage 4 proposals already marked in

core-js
as stable ECMAScript, they will be removed from proposals namespace in the next major
core-js
version. CommonJS entry points:
js
core-js(-pure)/stage/4
globalThis

Module

esnext.global-this
.

js
let globalThis: Object;
CommonJS entry points:
js
core-js/proposals/global-this
core-js(-pure)/features/global-this
Examples:
js
globalThis.Array === Array; // => true
String#matchAll

Module

esnext.string.match-all
.

class String {
  matchAll(regexp: RegExp): Iterator;
}

CommonJS entry points:

js
core-js/proposals/string-match-all
String#replaceAll

Module

esnext.string.replace-all

js
class String {
  replaceAll(searchValue: string | RegExp, replaceString: string | (searchValue, index, this) => string): string;
}
CommonJS entry points:
js
core-js/proposals/string-replace-all
core-js/features/string/replace-all
Examples:
js
'Test abc test test abc test.'.replaceAll('abc', 'foo'); // -> 'Test foo test test foo test.'
Promise.allSettled

Module

esnext.promise.all-settled

js
class Promise {
  static allSettled(iterable: Iterable): Promise;
}
CommonJS entry points:
js
core-js/proposals/promise-all-settled
Promise.any

Modules

esnext.promise.any
and
esnext.aggregate-error
```js class AggregateError { constructor(errors: Iterable, message: string): AggregateError; errors: Array; message: string; }

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

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/promise-any core-js(-pure)/features/promise/any core-js(-pure)/features/aggregate-error
[*Examples*](https://goo.gl/iErvmp):
js 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] ```

Stage 3 proposals

CommonJS entry points:

js
core-js(-pure)/stage/3
Relative indexing method

Modules

esnext.array.at
and
esnext.typed-array.at

Warning! Because of the conflict with another proposal, this method is not available on

String.prototype
in this version.

class Array {
  at(index: int): any;
}

class [ Int8Array, Uint8Array, Uint8ClampedArray, Int16Array, Uint16Array, Int32Array, Uint32Array, Float32Array, Float64Array, ] { at(index: int): any; }

CommonJS entry points:

core-js/proposals/relative-indexing-method
core-js(-pure)/features/array/at
core-js(-pure)/features/typed-array/at
Examples:
js
[1, 2, 3].at(1);  // => 2
[1, 2, 3].at(-1); // => 3

Stage 2 proposals

CommonJS entry points:

core-js(-pure)/stage/2
New
Set
methods

Modules

esnext.set.difference
,
esnext.set.intersection
,
esnext.set.is-disjoint-from
,
esnext.set.is-subset-of
,
esnext.set.is-superset-of
,
esnext.set.symmetric-difference
,
esnext.set.union

js
class Set {
  difference(iterable: Iterable): Set;
  intersection(iterable: Iterable): Set;
  isDisjointFrom(iterable: Iterable): boolean;
  isSubsetOf(iterable: Iterable): boolean;
  isSupersetOf(iterable: Iterable): boolean;
  symmetricDifference(iterable: Iterable): Set;
  union(iterable: Iterable): Set;
}
CommonJS entry points:
js
core-js/proposals/set-methods
core-js(-pure)/features/set/difference
core-js(-pure)/features/set/intersection
core-js(-pure)/features/set/is-disjoint-from
core-js(-pure)/features/set/is-subset-of
core-js(-pure)/features/set/is-superset-of
core-js(-pure)/features/set/symmetric-difference
core-js(-pure)/features/set/union
Examples: ```js new Set([1, 2, 3]).union([3, 4, 5]); // => Set {1, 2, 3, 4, 5} new Set([1, 2, 3]).intersection([3, 4, 5]); // => Set {3} new Set([1, 2, 3]).difference([3, 4, 5]); // => Set {1, 2} new Set([1, 2, 3]).symmetricDifference([3, 4, 5]); // => Set {1, 2, 4, 5}

new Set([1, 2, 3]).isDisjointFrom([4, 5, 6]); // => true new Set([1, 2, 3]).isSubsetOf([5, 4, 3, 2, 1]); // => true new Set([5, 4, 3, 2, 1]).isSupersetOf([1, 2, 3]); // => true ```

Symbol.{ asyncDispose, dispose }
for
using
statement

Modules

esnext.symbol.dispose
and
esnext.symbol.async-dispose
.

js
class Symbol {
  static asyncDispose: @@asyncDispose;
  static dispose: @@dispose;
}
CommonJS entry points:
js
core-js/proposals/using-statement
core-js(-pure)/features/symbol/async-dispose
core-js(-pure)/features/symbol/dispose
Array.isTemplateObject

Module

esnext.array.is-template-object

js
class Array {
  static isTemplateObject(value: any): boolean
}
CommonJS entry points:
js
core-js/proposals/array-is-template-object
core-js(-pure)/features/array/is-template-object
Example:
js
console.log(Array.isTemplateObject((it => it)`qwe${ 123 }asd`)); // => true
Iterator helpers

Modules

esnext.async-iterator.constructor
,
esnext.async-iterator.as-indexed-pairs
,
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.constructor
,
esnext.iterator.as-indexed-pairs
,
esnext.iterator.drop
,
esnext.iterator.every
,
esnext.iterator.filter
,
esnext.iterator.find
,
esnext.iterator.flat-map
,
esnext.iterator.for-each
,
esnext.iterator.from
,
esnext.iterator.map
,
esnext.iterator.reduce
,
esnext.iterator.some
,
esnext.iterator.take
and
esnext.iterator.to-array
```js class Iterator { static from(iterable: Iterable): Iterator; asIndexedPairs(): Iterator<[index, any]>; drop(limit: uint): Iterator; every(callbackfn: value: any => boolean): boolean; filter(callbackfn: value: any => boolean): Iterator; find(callbackfn: value: any => boolean)): any; flatMap(callbackfn: value => any: Iterable): Iterator; forEach(callbackfn: value => void): void; map(callbackfn: value => any): Iterator; reduce(callbackfn: (memo: any, value: any) => any, initialValue: any): any; some(callbackfn: value: any => boolean): boolean; take(limit: uint): Iterator; toArray(): Array; @@toStringTag: 'Iterator' }

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

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/iterator-helpers core-js(-pure)/features/async-iterator core-js(-pure)/features/async-iterator/as-indexed-pairs core-js(-pure)/features/async-iterator/drop core-js(-pure)/features/async-iterator/every core-js(-pure)/features/async-iterator/filter core-js(-pure)/features/async-iterator/find core-js(-pure)/features/async-iterator/flat-map core-js(-pure)/features/async-iterator/for-each core-js(-pure)/features/async-iterator/from core-js(-pure)/features/async-iterator/map core-js(-pure)/features/async-iterator/reduce core-js(-pure)/features/async-iterator/some core-js(-pure)/features/async-iterator/take core-js(-pure)/features/async-iterator/to-array core-js(-pure)/features/iterator core-js(-pure)/features/iterator/as-indexed-pairs core-js(-pure)/features/iterator/drop core-js(-pure)/features/iterator/every core-js(-pure)/features/iterator/filter core-js(-pure)/features/iterator/find core-js(-pure)/features/iterator/flat-map core-js(-pure)/features/iterator/for-each core-js(-pure)/features/iterator/from core-js(-pure)/features/iterator/map core-js(-pure)/features/iterator/reduce core-js(-pure)/features/iterator/some core-js(-pure)/features/iterator/take core-js(-pure)/features/iterator/to-array
[Examples](http://es6.zloirock.ru/#log(%5B1%2C%202%2C%203%2C%204%2C%205%2C%206%2C%207%5D.values()%0A%20%20.drop(1)%0A%20%20.take(5)%0A%20%20.filter(it%20%3D%3E%20it%20%25%202)%0A%20%20.map(it%20%3D%3E%20it%20**%202)%0A%20%20.toArray())%3B%20%2F%2F%20%3D%3E%20%5B9%2C%2025%5D%0A%0Alog(Iterator.from(%7B%0A%20%20next%3A%20()%20%3D%3E%20(%7B%20done%3A%20Math.random()%20%3E%20.9%2C%20value%3A%20Math.random()%20*%2010%20%7C%200%20%7D)%0A%7D).toArray())%3B%20%2F%2F%20%3D%3E%20%5B7%2C%206%2C%203%2C%200%2C%202%2C%208%5D%0A%0AAsyncIterator.from(%5B1%2C%202%2C%203%2C%204%2C%205%2C%206%2C%207%5D)%0A%20%20.drop(1)%0A%20%20.take(5)%0A%20%20.filter(it%20%3D%3E%20it%20%25%202)%0A%20%20.map(it%20%3D%3E%20it%20**%202)%0A%20%20.toArray()%0A%20%20.then(log)%3B%20%2F%2F%20%3D%3E%20%5B9%2C%2025%5D):
js [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() > .9, value: Math.random() * 10 | 0 }) }).toArray(); // => [7, 6, 3, 0, 2, 8]

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

Caveats:
  • For preventing prototypes pollution, in the
    pure
    version, new
    %IteratorPrototype%
    methods are not added to the real
    %IteratorPrototype%
    , they available only on wrappers - instead of
    [].values().map(fn)
    use
    Iterator.from([]).map(fn)
    .
  • Now, we have access to the real
    %AsyncIteratorPrototype%
    only with usage async generators syntax. So, for compatibility the library with old browsers, we should use
    Function
    constructor. However, that breaks compatibility with CSP. So, if you wanna use the real
    %AsyncIteratorPrototype%
    , you should set
    USE_FUNCTION_CONSTRUCTOR
    option in the
    core-js/configurator
    to
    true
    : ```js const configurator = require('core-js/configurator');

configurator({ USEFUNCTIONCONSTRUCTOR: true });

require('core-js');

(async function * () { /* empty */ })() instanceof AsyncIterator; // => true ```

Map#emplace

Modules

esnext.map.emplace
and
esnext.weak-map.emplace
```js class Map { emplace(key: any, { update: (value: any, key: any, handler: object) => updated: any, insert: (key: any, handler: object) => value: any): updated | value; }

class WeakMap { emplace(key: any, { update: (value: any, key: any, handler: object) => updated: any, insert: (key: any, handler: object) => value: any): updated | value; }

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/map-upsert core-js(-pure)/features/map/emplace core-js(-pure)/features/weak-map/emplace
[*Examples*](http://es6.zloirock.ru/#const%20map%20%3D%20new%20Map(%5B%5B'a'%2C%202%5D%5D)%3B%0A%0Amap.emplace('a'%2C%20%7B%20update%3A%20it%20%3D%3E%20it%20**%202%2C%20insert%3A%20()%20%3D%3E%203%7D)%3B%20%2F%2F%20%3D%3E%204%0A%0Amap.emplace('b'%2C%20%7B%20update%3A%20it%20%3D%3E%20it%20**%202%2C%20insert%3A%20()%20%3D%3E%203%7D)%3B%20%2F%2F%20%3D%3E%203%0A%0Afor%20(let%20%5Bkey%2C%20value%5D%20of%20map)%7B%0A%20%20log(key%2C%20value)%3B%20%2F%2F%20%3D%3E%20Map%20%7B%20'a'%3A%204%2C%20'b'%3A%203%20%7D%0A%7D):
js const map = new Map([['a', 2]]);

map.emplace('a', { update: it => it ** 2, insert: () => 3}); // => 4

map.emplace('b', { update: it => it ** 2, insert: () => 3}); // => 3

console.log(map); // => Map { 'a': 4, 'b': 3 } ```

Stage 1 proposals

CommonJS entry points:

js
core-js(-pure)/stage/1
Getting last item from
Array

Modules

esnext.array.last-item
and
esnext.array.last-index

js
class Array {
  attribute lastItem: any;
  readonly attribute lastIndex: uint;
}
CommonJS entry points:
js
core-js/proposals/array-last
core-js/features/array/last-item
core-js/features/array/last-index
Examples: ```js [1, 2, 3].lastItem; // => 3 [1, 2, 3].lastIndex; // => 2

const array = [1, 2, 3]; array.lastItem = 4;

array; // => [1, 2, 4] ```

Promise.try

Module

esnext.promise.try

js
class Promise {
  static try(callbackfn: Function): promise;
}
CommonJS entry points:
js
core-js/proposals/promise-try
core-js(-pure)/features/promise/try
Examples: ``
js
Promise.try(() => 42).then(it => console.log(
Promise, resolved as ${it}`));

Promise.try(() => { throw 42; }).catch(it => console.log(

Promise, rejected as ${it}
)); ```

New collections methods:

New
Set
and
Map
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.group-by
,
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
```js class Set { static of(...args: Array): Set; static from(iterable: Iterable, mapFn?: (value: any, index: number) => any, thisArg?: any): Set; addAll(...args: Array): this; deleteAll(...args: Array): 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 groupBy(iterable: Iterable, callbackfn?: (value: any) => any): Map; static of(...args: Array<[key, value]>): Map; static from(iterable: Iterable, mapFn?: (value: any, index: number) => [key: any, value: any], thisArg?: any): Map; static keyBy(iterable: Iterable, callbackfn?: (value: any) => any): Map; deleteAll(...args: Array): 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): 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): WeakSet; static from(iterable: Iterable, mapFn?: (value: any, index: number) => Object, thisArg?: any): WeakSet; addAll(...args: Array): this; deleteAll(...args: Array): boolean; }

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

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/collection-methods core-js/proposals/collection-of-from core-js(-pure)/features/set/add-all core-js(-pure)/features/set/delete-all core-js(-pure)/features/set/every core-js(-pure)/features/set/filter core-js(-pure)/features/set/find core-js(-pure)/features/set/from core-js(-pure)/features/set/join core-js(-pure)/features/set/map core-js(-pure)/features/set/of core-js(-pure)/features/set/reduce core-js(-pure)/features/set/some core-js(-pure)/features/map/delete-all core-js(-pure)/features/map/every core-js(-pure)/features/map/filter core-js(-pure)/features/map/find core-js(-pure)/features/map/find-key core-js(-pure)/features/map/from core-js(-pure)/features/map/group-by core-js(-pure)/features/map/includes core-js(-pure)/features/map/key-by core-js(-pure)/features/map/key-of core-js(-pure)/features/map/map-keys core-js(-pure)/features/map/map-values core-js(-pure)/features/map/merge core-js(-pure)/features/map/of core-js(-pure)/features/map/reduce core-js(-pure)/features/map/some core-js(-pure)/features/map/update core-js(-pure)/features/weak-set/add-all core-js(-pure)/features/weak-set/delete-all core-js(-pure)/features/weak-set/of core-js(-pure)/features/weak-set/from core-js(-pure)/features/weak-map/delete-all core-js(-pure)/features/weak-map/of core-js(-pure)/features/weak-map/from
`.of` / `.from` [*examples*](https://goo.gl/mSC7eU):
js 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
methods

Modules

esnext.composite-key
and
esnext.composite-symbol

js
function compositeKey(...args: Array): object;
function compositeSymbol(...args: Array): symbol;
CommonJS entry points:
js
core-js/proposals/keys-composition
core-js(-pure)/features/composite-key
core-js(-pure)/features/composite-symbol
Examples: ```js // 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'];

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 ```

Observable

Modules

esnext.observable
and
esnext.symbol.observable
```js class Observable { constructor(subscriber: Function): Observable; subscribe(observer: Function | { next?: Function, error?: Function, complete?: Function }): Subscription; @@observable(): this; static of(...items: Aray): Observable; static from(x: Observable | Iterable): Observable; static readonly attribute @@species: this; }

class Symbol { static observable: @@observable; }

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/observable core-js(-pure)/features/observable core-js(-pure)/features/symbol/observable
[*Examples*](http://goo.gl/1LDywi):
js new Observable(observer => { observer.next('hello'); observer.next('world'); observer.complete(); }).subscribe({ next(it) { console.log(it); }, complete() { console.log('!'); } }); ```
Math
extensions

Modules

esnext.math.clamp
,
esnext.math.deg-per-rad
,
esnext.math.degrees
,
esnext.math.fscale
,
esnext.math.rad-per-deg
,
esnext.math.radians
and
esnext.math.scale

js
namespace Math {
  DEG_PER_RAD: number;
  RAD_PER_DEG: number;
  clamp(x: number, lower: number, upper: number): number;
  degrees(radians: number): number;
  fscale(x: number, inLow: number, inHigh: number, outLow: number, outHigh: number): number;
  radians(degrees: number): number;
  scale(x: number, inLow: number, inHigh: number, outLow: number, outHigh: number): number;
}
CommonJS entry points:
js
core-js/proposals/math-extensions
core-js(-pure)/features/math/clamp
core-js(-pure)/features/math/deg-per-rad
core-js(-pure)/features/math/degrees
core-js(-pure)/features/math/fscale
core-js(-pure)/features/math/rad-per-deg
core-js(-pure)/features/math/radians
core-js(-pure)/features/math/scale
Math.signbit

Module

esnext.math.signbit

js
namespace Math {
  signbit(x: number): boolean;
}
CommonJS entry points:
js
core-js/proposals/math-signbit
core-js(-pure)/features/math/signbit
Examples:
js
Math.signbit(NaN); // => false
Math.signbit(1);   // => false
Math.signbit(-1);  // => true
Math.signbit(0);   // => false
Math.signbit(-0);  // => true
Number.fromString

Module

esnext.number.from-string

js
class Number {
  fromString(string: string, radix: number): number;
}
CommonJS entry points:
js
core-js/proposals/number-from-string
core-js(-pure)/features/number/from-string
Number.range

Module

esnext.number.range
and
esnext.bigint.range
```js class Number { range(start: number, end: number, options: { step: number = 1, inclusive: boolean = false } | step: number = 1): RangeIterator; }

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

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/number-range core-js(-pure)/features/bigint/range core-js(-pure)/features/number/range
[*Example*](http://es6.zloirock.ru/#for%20(const%20i%20of%20Number.range(1%2C%2010%2C%20%7B%20step%3A%203%2C%20inclusive%3A%20true%20%7D))%20%7B%0A%20%20log(i)%3B%20%2F%2F%20%3D%3E%201%2C%204%2C%207%2C%2010%0A%7D):
js for (const i of Number.range(1, 10)) { console.log(i); // => 1, 2, 3, 4, 5, 6, 7, 8, 9 }

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

String#codePoints

Module

esnext.string.code-points

js
class String {
  codePoints(): Iterator;
}
CommonJS entry points:
js
core-js/proposals/string-code-points
core-js(-pure)/features/string/code-points
Example:
js
for (let { codePoint, position } of 'qwe'.codePoints()) {
  console.log(codePoint); // => 113, 119, 101
  console.log(position);  // => 0, 1, 2
}
Seeded pseudo-random numbers

Module

esnext.math.seeded-prng

js
class Math {
  seededPRNG({ seed: number }): Iterator;
}
CommonJS entry points:
js
core-js/proposals/seeded-random
core-js(-pure)/features/math/seeded-prng
Example:
js
for (let x of Math.seededPRNG({ seed: 42 })) {
  console.log(x); // => 0.16461519912315087, 0.2203933906000046, 0.8249682894209105
  if (x > .8) break;
}
Symbol.patternMatch
for pattern matching

Module

esnext.symbol.pattern-match
.

js
class Symbol {
  static patternMatch: @@patternMatch;
}
CommonJS entry points:
js
core-js/proposals/pattern-matching
core-js(-pure)/features/symbol/pattern-match
Object iteration

Modules

esnext.object.iterate-keys
,
esnext.object.iterate-values
,
esnext.object.iterate-entries
.

js
class Object {
  iterateKeys(object: any): Iterator;
  iterateValues(object: any): Iterator;
  iterateEntries(object: any): Iterator;
}
CommonJS entry points:
js
core-js/proposals/object-iteration
core-js(-pure)/features/object/iterate-keys
core-js(-pure)/features/object/iterate-values
core-js(-pure)/features/object/iterate-entries
Example: ```js const obj = { foo: 'bar', baz: 'blah' };

for (const [key, value] of Object.iterateEntries(obj)) { console.log(

${key} -> ${value}
); }

for (const key of Object.iterateKeys(obj)) { console.log(key); }

for (const value of Object.iterateValues(obj)) { console.log(value); } ```

Array filtering

Modules

esnext.array.filter-out
and
esnext.typed-array.filter-out
. ```js class Array { filterOut(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): Array; }

class [ Int8Array, Uint8Array, Uint8ClampedArray, Int16Array, Uint16Array, Int32Array, Uint32Array, Float32Array, Float64Array, ] { filterOut(callbackfn: (value: number, index: number, target: %TypedArray%) => boolean, thisArg?: any): %TypedArray%; }

[*CommonJS entry points:*](#commonjs-api)
core-js/proposals/array-filtering core-js(-pure)/features/array/filter-out core-js(-pure)/features/array/virtual/filter-out core-js(-pure)/features/typed-array/filter-out core-js(-pure)/features/typed-array/virtual/filter-out
[*Examples*](http://es6.zloirock.ru/#log(%5B1%2C%202%2C%203%2C%204%2C%205%5D.filterOut(it%20%3D%3E%20it%20%25%202))%3B%20%2F%2F%20%3D%3E%20%5B2%2C%204%5D):
js [1, 2, 3, 4, 5].filterOut(it => it % 2); // => [2, 4] ````
Array deduplication

Module

esnext.array.unique-by

js
class Array {
  uniqueBy(resolver?: (item: any) => any): Array;
}
CommonJS entry points:
core-js/proposals/array-unique
core-js(-pure)/features/array/unique-by
core-js(-pure)/features/array/virtual/unique-by
Examples: ```js [1, 2, 3, 2, 1].uniqueBy(); // [1, 2, 3]

[ { id: 1, uid: 10000 }, { id: 2, uid: 10000 }, { id: 3, uid: 10001 } ].uniqueBy(it => it.id); // => [{ id: 1, uid: 10000 }, { id: 3, uid: 10001 }] ```

Stage 0 proposals

CommonJS entry points:

js
core-js(-pure)/stage/0
URL

See more info in web standards namespace

String#at

Module

esnext.string.at

js
class String {
  at(index: number): string;
}
CommonJS entry points:
js
core-js/proposals/string-at
core-js(-pure)/features/string/at
core-js(-pure)/features/string/virtual/at
Examples:
js
'a𠮷b'.at(1);        // => '𠮷'
'a𠮷b'.at(1).length; // => 2
Efficient 64 bit arithmetic

Modules

esnext.math.iaddh
,
esnext.math.isubh
,
esnext.math.imulh
and
esnext.math.umulh

js
namespace Math {
  iaddh(lo0: number, hi0: number, lo1: number, hi1: number): number;
  isubh(lo0: number, hi0: number, lo1: number, hi1: number): number;
  imulh(a: number, b: number): number;
  umulh(a: number, b: number): number;
}
CommonJS entry points:
js
core-js/proposals/efficient-64-bit-arithmetic
core-js(-pure)/features/math/iaddh
core-js(-pure)/features/math/isubh
core-js(-pure)/features/math/imulh
core-js(-pure)/features/math/umulh

Pre-stage 0 proposals

CommonJS entry points:

js
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
.

js
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;
  getOwnMetadataKeys(target: Object, propertyKey?: PropertyKey): Array;
  metadata(metadataKey: any, metadataValue: any): decorator(target: Object, targetKey?: PropertyKey) => void;
}
CommonJS entry points:
js
core-js/proposals/reflect-metadata
core-js(-pure)/features/reflect/define-metadata
core-js(-pure)/features/reflect/delete-metadata
core-js(-pure)/features/reflect/get-metadata
core-js(-pure)/features/reflect/get-metadata-keys
core-js(-pure)/features/reflect/get-own-metadata
core-js(-pure)/features/reflect/get-own-metadata-keys
core-js(-pure)/features/reflect/has-metadata
core-js(-pure)/features/reflect/has-own-metadata
core-js(-pure)/features/reflect/metadata
Examples:
js
let object = {};
Reflect.defineMetadata('foo', 'bar', object);
Reflect.ownKeys(object);               // => []
Reflect.getOwnMetadataKeys(object);    // => ['foo']
Reflect.getOwnMetadata('foo', object); // => 'bar'

Web standards

CommonJS entry points:

js
core-js(-pure)/web

setTimeout
and
setInterval

Module

web.timers
. Additional arguments fix for IE9-.

js
function setTimeout(callback: any, time: any, ...args: Array): number;
function setInterval(callback: any, time: any, ...args: Array): number;
CommonJS entry points:
js
core-js(-pure)/web/timers
core-js(-pure)/stable|features/set-timeout
core-js(-pure)/stable|features/set-interval
js
// Before:
setTimeout(log.bind(null, 42), 1000);
// After:
setTimeout(log, 1000, 42);

setImmediate

Module

web.immediate
.
setImmediate
polyfill.

js
function setImmediate(callback: any, ...args: Array): number;
function clearImmediate(id: number): void;
CommonJS entry points:
js
core-js(-pure)/web/immediate
core-js(-pure)/stable|features/set-immediate
core-js(-pure)/stable|features/clear-immediate
Examples: ```js 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

js
function queueMicrotask(fn: Function): void;
CommonJS entry points:
js
core-js/web/queue-microtask
core-js(-pure)/stable|features/queue-microtask
Examples:
js
queueMicrotask(() => console.log('called as microtask'));

URL
and
URLSearchParams

URL
standard implementation. Modules
web.url
,
web.url.to-json
,
web.url-search-params
. ```js 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; }

class URLSearchParams { constructor(params?: string | Iterable<[key, value]> | Object); append(name: string, value: string): void; delete(name: string): void; get(name: string): string | void; getAll(name: string): Array; has(name: 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; values(): Iterator; @@iterator(): Iterator<[key, value]>; }

[*CommonJS entry points:*](#commonjs-api)
js core-js/proposals/url core-js(-pure)/web/url core-js(-pure)/web/url-search-params core-js(-pure)/stable|features/url core-js/stable|features/url/to-json core-js(-pure)/stable|features/url-search-params core-js/stable|features/url-search-params/sort
[*Examples*](https://goo.gl/kksjwV):
js const url = new URL('http://login:[email protected]:8080/foo/bar?a=1&b=2&a=3#fragment');

console.log(url.href); // => 'http://login:[email protected]:8080/foo/bar?a=1&b=2#fragment' console.log(url.origin); // => 'http://example.com:8080' console.log(url.protocol); // => 'http:' 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()); // => 'http://login:[email protected]:8080/foo/bar?a=1&b=2&a=3#fragment' console.log(url.toString()); // => 'http://login:[email protected]:8080/foo/bar?a=1&b=2&a=3#fragment'

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

url.pathname = ''; url.searchParams.append('c', 3);

console.log(url.search); // => '?a=1&b=2&c=3' console.log(url.href); // => 'http://login:[email protected]:8080/?a=1&a=3&b=2&c=4#fragment'

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

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

for (let [key, value] of params) { console.log(key); // => 'a', 'a', 'a', 'b', 'c' console.log(value); // => '1', '3', '2', '2', '4' }

console.log(params.toString()); // => 'a=1&a=3&a=2&b=2&c=4' ```

Caveats when using
URL
and
URLSearchParams
:
  • IE8 does not support setters, so they do not work on
    URL
    instances. However,
    URL
    constructor can be used for basic
    URL
    parsing.
  • Legacy encodings in a search query are not supported. Also,
    core-js
    implementation has some other encoding-related issues.
  • URL
    implementations from all of the popular browsers have much more problems than
    core-js
    , however, replacing all of them does not looks like a good idea. You can customize the aggressiveness of polyfill by your requirements.

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
. ```js 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; }

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

[*CommonJS entry points:*](#commonjs-api)
js core-js(-pure)/web/dom-collections core-js(-pure)/stable|features/dom-collections/iterator core-js/stable|features/dom-collections/for-each
[*Examples*](http://goo.gl/lfXVFl):
js 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

Modules

core.is-iterable
,
core.get-iterator
,
core.get-iterator-method
- helpers for check iterability / get iterator in the

pure
version or, for example, for
arguments
object:
js
function isIterable(value: any): boolean;
function getIterator(value: any): Object;
function getIteratorMethod(value: any): Function | void;
CommonJS entry points:
js
core-js-pure/features/is-iterable
core-js-pure/features/get-iterator
core-js-pure/features/get-iterator-method
Examples: ```js import isIterable from 'core-js-pure/features/is-iterable'; import getIterator from 'core-js-pure/features/get-iterator'; import getIteratorMethod from 'core-js-pure/features/get-iterator-method';

let list = (function () { 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' let 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

  • ES
    String#normalize
    is not a very useful feature, but this polyfill will be very large. If you need it, you can use unorm.
  • ES
    Proxy
    can't be polyfilled, you can try
    proxy-polyfill
    which provides a very little subset of features.
  • window.fetch
    is not a cross-platform feature, in some environments, it makes no sense. For this reason, I don't think it should be in
    core-js
    . Looking at a large number of requests it might be added in the future. Now you can use, for example, this polyfill.
  • ECMA-402
    Intl
    is missed because of the size. You can use this polyfill.

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