https://github.com/zloirock/core-js
Standard Library
https://github.com/zloirock/core-js
ecmascript-proposals es2015 es2019 es6 es7 esnext javascript js polyfill ponyfill promise proposal proposals shim symbol weakmap
Last synced: about 2 months ago
JSON representation
Standard Library
- Host: GitHub
- URL: https://github.com/zloirock/core-js
- Owner: zloirock
- License: mit
- Created: 2013-07-17T16:32:27.000Z (almost 13 years ago)
- Default Branch: master
- Last Pushed: 2025-05-05T05:27:12.000Z (about 1 year ago)
- Last Synced: 2025-05-05T09:44:35.464Z (about 1 year ago)
- Topics: ecmascript-proposals, es2015, es2019, es6, es7, esnext, javascript, js, polyfill, ponyfill, promise, proposal, proposals, shim, symbol, weakmap
- Language: JavaScript
- Homepage:
- Size: 63.7 MB
- Stars: 24,972
- Watchers: 256
- Forks: 1,671
- Open Issues: 46
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- Funding: .github/FUNDING.yml
- License: LICENSE
- Security: SECURITY.md
Awesome Lists containing this project
- favorite-link - 标准图书馆。
- awesome-ponyfills - core-js-pure - The entire standard library. (Main)
- StarryDivineSky - zloirock/core-js
- es6-tools - core-js - Modular and compact polyfills for ES6 including Symbols, Map, Set, Iterators, Promises, setImmediate, Array generics, etc. The standard library used by [Babel](https://github.com/babel/babel). (Polyfills / Brunch Plugins)
- awesome-ru - Core-js - Модульная стандартная библиотека для JavaScript с полифилами. Автор: Денис Пушкарев. (Инструменты разработчика)
- awesome-list - core-js
- fucking-es6-tools - core-js - Modular and compact polyfills for ES6 including Symbols, Map, Set, Iterators, Promises, setImmediate, Array generics, etc. The standard library used by <b><code> 43792⭐</code></b> <b><code> 5777🍴</code></b> [Babel](https://github.com/babel/babel)). (Polyfills / Brunch Plugins)
- awesome - core-js - Modular standard library for JavaScript. (front-end-development)
- awesome - zloirock/core-js - Standard Library (JavaScript)
- awesome-starred - zloirock/core-js - Standard Library (JavaScript)
- awesome - core-js - Standard Library (JavaScript)
- my-awesome - zloirock/core-js - proposals,es2015,es6,es7,esnext,javascript,js,polyfill,ponyfill,proposal,proposals,shim pushed_at:2026-04 star:25.5k fork:1.7k Standard Library (JavaScript)
- awesome - zloirock/core-js - Standard Library (JavaScript)
- awesome-github-star - core-js
README
[](https://opencollective.com/core-js) [](https://github.com/zloirock/core-js/blob/master/CONTRIBUTING.md) [](https://www.npmjs.com/package/core-js) [](https://npm-stat.com/charts.html?package=core-js&package=core-js-pure&package=core-js-compat&from=2014-11-18) [](https://npm-stat.com/charts.html?package=core-js&package=core-js-pure&package=core-js-compat&from=2014-11-18)
**Welcome to our new website, [core-js.io](https://core-js.io), where our documentation is moving!**
---
**I highly recommend reading this: [So, what's next?](https://core-js.io/blog/2023-02-14-so-whats-next)**
---
> Modular standard library for JavaScript. Includes polyfills for [ECMAScript up to 2025](#ecmascript): [promises](#ecmascript-promise), [symbols](#ecmascript-symbol), [collections](#ecmascript-collections), iterators, [typed arrays](#ecmascript-typed-arrays), many other features, [ECMAScript proposals](#ecmascript-proposals), [some cross-platform WHATWG / W3C features and proposals](#web-standards) like [`URL`](#url-and-urlsearchparams). You can load only required features or use it without global namespace pollution.
## [core-js@3, babel and a look into the future](https://core-js.io/blog/2019-03-19-core-js-3-babel-and-a-look-into-the-future)
## Raising funds
`core-js` isn't backed by a company, so the future of this project depends on you. Become a sponsor or a backer if you are interested in `core-js`: [**Open Collective**](https://opencollective.com/core-js), [**Patreon**](https://patreon.com/zloirock), [**Boosty**](https://boosty.to/zloirock), **Bitcoin ( bc1qlea7544qtsmj2rayg0lthvza9fau63ux0fstcz )**, [**Alipay**](https://user-images.githubusercontent.com/2213682/219464783-c17ad329-17ce-4795-82a7-f609493345ed.png).
---
---
---
[*Example of usage*](https://tinyurl.com/28zqjbun):
```js
import 'core-js/actual';
Promise.try(() => 42).then(it => console.log(it)); // => 42
Array.from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]
[1, 2].flatMap(it => [it, it]); // => [1, 1, 2, 2]
Iterator.concat([1, 2], function * (i) { while (true) yield i++; }(3))
.drop(1).take(5)
.filter(it => it % 2)
.map(it => it ** 2)
.toArray(); // => [9, 25]
structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])
```
*You can load only required features*:
```js
import 'core-js/actual/promise';
import 'core-js/actual/set';
import 'core-js/actual/iterator';
import 'core-js/actual/array/from';
import 'core-js/actual/array/flat-map';
import 'core-js/actual/structured-clone';
Promise.try(() => 42).then(it => console.log(it)); // => 42
Array.from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]
[1, 2].flatMap(it => [it, it]); // => [1, 1, 2, 2]
Iterator.concat([1, 2], function * (i) { while (true) yield i++; }(3))
.drop(1).take(5)
.filter(it => it % 2)
.map(it => it ** 2)
.toArray(); // => [9, 25]
structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])
```
*Or use it without global namespace pollution*:
```js
import Promise from 'core-js-pure/actual/promise';
import Set from 'core-js-pure/actual/set';
import Iterator from 'core-js-pure/actual/iterator';
import from from 'core-js-pure/actual/array/from';
import flatMap from 'core-js-pure/actual/array/flat-map';
import structuredClone from 'core-js-pure/actual/structured-clone';
Promise.try(() => 42).then(it => console.log(it)); // => 42
from(new Set([1, 2, 3]).union(new Set([3, 4, 5]))); // => [1, 2, 3, 4, 5]
flatMap([1, 2], it => [it, it]); // => [1, 1, 2, 2]
Iterator.concat([1, 2], function * (i) { while (true) yield i++; }(3))
.drop(1).take(5)
.filter(it => it % 2)
.map(it => it ** 2)
.toArray(); // => [9, 25]
structuredClone(new Set([1, 2, 3])); // => new Set([1, 2, 3])
```
### Index
- [Usage](#usage)
- [Installation](#installation)
- [`postinstall` message](#postinstall-message)
- [CommonJS API](#commonjs-api)
- [Babel](#babel)
- [`@babel/polyfill`](#babelpolyfill)
- [`@babel/preset-env`](#babelpreset-env)
- [`@babel/runtime`](#babelruntime)
- [swc](#swc)
- [Configurable level of aggressiveness](#configurable-level-of-aggressiveness)
- [Custom build](#custom-build)
- [Supported engines and compatibility data](#supported-engines-and-compatibility-data)
- [Features](#features)
- [ECMAScript](#ecmascript)
- [ECMAScript: Object](#ecmascript-object)
- [ECMAScript: Function](#ecmascript-function)
- [ECMAScript: Error](#ecmascript-error)
- [ECMAScript: Array](#ecmascript-array)
- [ECMAScript: Iterator](#ecmascript-iterator)
- [ECMAScript: String and RegExp](#ecmascript-string-and-regexp)
- [ECMAScript: Number](#ecmascript-number)
- [ECMAScript: Math](#ecmascript-math)
- [ECMAScript: Date](#ecmascript-date)
- [ECMAScript: Promise](#ecmascript-promise)
- [ECMAScript: Symbol](#ecmascript-symbol)
- [ECMAScript: Collections](#ecmascript-collections)
- [ECMAScript: Explicit Resource Management](#ecmascript-explicit-resource-management)
- [ECMAScript: Typed Arrays](#ecmascript-typed-arrays)
- [ECMAScript: Reflect](#ecmascript-reflect)
- [ECMAScript: JSON](#ecmascript-json)
- [ECMAScript: globalThis](#ecmascript-globalthis)
- [ECMAScript proposals](#ecmascript-proposals)
- [Finished proposals](#finished-proposals)
- [`globalThis`](#globalthis)
- [Relative indexing method](#relative-indexing-method)
- [`Array.prototype.includes`](#arrayprototypeincludes)
- [`Array.prototype.flat` / `Array.prototype.flatMap`](#arrayprototypeflat--arrayprototypeflatmap)
- [`Array` find from last](#array-find-from-last)
- [Change `Array` by copy](#change-array-by-copy)
- [`Array` grouping](#array-grouping)
- [`Array.fromAsync`](#arrayfromasync)
- [`ArrayBuffer.prototype.transfer` and friends](#arraybufferprototypetransfer-and-friends)
- [`Uint8Array` to / from base64 and hex](#uint8array-to--from-base64-and-hex)
- [`Error.isError`](#erroriserror)
- [Explicit Resource Management](#explicit-resource-management)
- [`Float16` methods](#float16-methods)
- [`Iterator` helpers](#iterator-helpers)
- [`Iterator` sequencing](#iterator-sequencing)
- [`Object.values` / `Object.entries`](#objectvalues--objectentries)
- [`Object.fromEntries`](#objectfromentries)
- [`Object.getOwnPropertyDescriptors`](#objectgetownpropertydescriptors)
- [Accessible `Object.prototype.hasOwnProperty`](#accessible-objectprototypehasownproperty)
- [`String` padding](#string-padding)
- [`String.prototype.matchAll`](#stringmatchall)
- [`String.prototype.replaceAll`](#stringreplaceall)
- [`String.prototype.trimStart` / `String.prototype.trimEnd`](#stringprototypetrimstart-stringprototypetrimend)
- [`RegExp` `s` (`dotAll`) flag](#regexp-s-dotall-flag)
- [`RegExp` named capture groups](#regexp-named-capture-groups)
- [`RegExp` escaping](#regexp-escaping)
- [`Promise.allSettled`](#promiseallsettled)
- [`Promise.any`](#promiseany)
- [`Promise.prototype.finally`](#promiseprototypefinally)
- [`Promise.try`](#promisetry)
- [`Promise.withResolvers`](#promisewithresolvers)
- [`Symbol.asyncIterator` for asynchronous iteration](#symbolasynciterator-for-asynchronous-iteration)
- [`Symbol.prototype.description`](#symbolprototypedescription)
- [`JSON.parse` source text access](#jsonparse-source-text-access)
- [Well-formed `JSON.stringify`](#well-formed-jsonstringify)
- [Well-formed unicode strings](#well-formed-unicode-strings)
- [New `Set` methods](#new-set-methods)
- [`Map` upsert](#map-upsert)
- [`Math.sumPrecise`](#mathsumprecise)
- [Stage 3 proposals](#stage-3-proposals)
- [Joint iteration](#joint-iteration)
- [`Symbol.metadata` for decorators metadata proposal](#symbolmetadata-for-decorators-metadata-proposal)
- [Stage 2.7 proposals](#stage-27-proposals)
- [`Iterator` chunking](#iterator-chunking)
- [Stage 2 proposals](#stage-2-proposals)
- [`AsyncIterator` helpers](#asynciterator-helpers)
- [`Iterator.range`](#iteratorrange)
- [`Array.isTemplateObject`](#arrayistemplateobject)
- [`Number.prototype.clamp`](#numberprototypeclamp)
- [`String.dedent`](#stringdedent)
- [`Symbol` predicates](#symbol-predicates)
- [`Symbol.customMatcher` for extractors](#symbolcustommatcher-for-extractors)
- [Stage 1 proposals](#stage-1-proposals)
- [`Observable`](#observable)
- [New collections methods](#new-collections-methods)
- [`.of` and `.from` methods on collection constructors](#of-and-from-methods-on-collection-constructors)
- [`compositeKey` and `compositeSymbol`](#compositekey-and-compositesymbol)
- [`Array` filtering](#array-filtering)
- [`Array` deduplication](#array-deduplication)
- [`DataView` get / set `Uint8Clamped` methods](#dataview-get-set-iint8clamped-methods)
- [`Number.fromString`](#numberfromstring)
- [`String.cooked`](#stringcooked)
- [`String.prototype.codePoints`](#stringprototypecodepoints)
- [`Symbol.customMatcher` for pattern matching](#symbolcustommatcher-for-pattern-matching)
- [Stage 0 proposals](#stage-0-proposals)
- [`Function.prototype.demethodize`](#functionprototypedemethodize)
- [`Function.{ isCallable, isConstructor }`](#function-iscallable-isconstructor-)
- [Pre-stage 0 proposals](#pre-stage-0-proposals)
- [`Reflect` metadata](#reflect-metadata)
- [Web standards](#web-standards)
- [`self`](#self)
- [`structuredClone`](#structuredclone)
- [Base64 utility methods](#base64-utility-methods)
- [`setTimeout` and `setInterval`](#settimeout-and-setinterval)
- [`setImmediate`](#setimmediate)
- [`queueMicrotask`](#queuemicrotask)
- [`URL` and `URLSearchParams`](#url-and-urlsearchparams)
- [`DOMException`](#domexception)
- [iterable DOM collections](#iterable-dom-collections)
- [Iteration helpers](#iteration-helpers)
- [Missing polyfills](#missing-polyfills)
- [Contributing](./CONTRIBUTING.md)
- [Security policy](https://github.com/zloirock/core-js/blob/master/SECURITY.md)
- [Changelog](./CHANGELOG.md)
## Usage[⬆](#index)
### Installation:[⬆](#index)
```sh
// global version
npm install --save core-js@3.49.0
// version without global namespace pollution
npm install --save core-js-pure@3.49.0
// bundled global version
npm install --save core-js-bundle@3.49.0
```
### `postinstall` message[⬆](#index)
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:
```sh
ADBLOCK=true npm install
// or
DISABLE_OPENCOLLECTIVE=true npm install
// or
npm install --loglevel silent
```
### CommonJS API[⬆](#index)
You can import only-required-for-you polyfills, like in the examples at the top of `README.md`. Available CommonJS entry points for all polyfilled methods / constructors and namespaces. Just some examples:
```ts
// polyfill all `core-js` features, including early-stage proposals:
import "core-js";
// or:
import "core-js/full";
// polyfill all actual features - stable ES, web standards and stage 3 ES proposals:
import "core-js/actual";
// polyfill only stable features - ES and web standards:
import "core-js/stable";
// polyfill only stable ES features:
import "core-js/es";
// if you want to polyfill `Set`:
// all `Set`-related features, with early-stage ES proposals:
import "core-js/full/set";
// stable required for `Set` ES features, features from web standards and stage 3 ES proposals:
import "core-js/actual/set";
// stable required for `Set` ES features and features from web standards
// (DOM collections iterator in this case):
import "core-js/stable/set";
// only stable ES features required for `Set`:
import "core-js/es/set";
// the same without global namespace pollution:
import Set from "core-js-pure/full/set";
import Set from "core-js-pure/actual/set";
import Set from "core-js-pure/stable/set";
import Set from "core-js-pure/es/set";
// if you want to polyfill just the required methods:
import "core-js/full/set/intersection";
import "core-js/actual/array/find-last";
import "core-js/stable/queue-microtask";
import "core-js/es/array/from";
// polyfill iterator helpers proposal:
import "core-js/proposals/iterator-helpers";
// polyfill all stage 2+ proposals:
import "core-js/stage/2";
```
> [!TIP]
> The usage of the `/actual/` namespace is recommended since it includes all actual JavaScript features and does not include unstable early-stage proposals that are available mainly for experiments.
> [!WARNING]
> - The `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 to 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](https://github.com/zloirock/core-js/search?q=Google+Maps&type=Issues).
> - Such conflicts are also resolvable by discovering and manually 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 a usage loader for each file, otherwise, you will have hundreds of requests.
#### CommonJS and prototype methods without global namespace pollution[⬆](#index)
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](https://github.com/tc39/proposal-bind-operator). Special for that, available `/virtual/` entry points. Example:
```ts
import fill from 'core-js-pure/actual/array/virtual/fill';
import findIndex from 'core-js-pure/actual/array/virtual/find-index';
Array(10)::fill(0).map((a, b) => b * b)::findIndex(it => it && !(it % 8)); // => 4
```
> [!WARNING]
> The bind operator is an early-stage ECMAScript proposal and usage of this syntax can be dangerous.
### Babel[⬆](#index)
`core-js` is integrated with `babel` and is the base for polyfilling-related `babel` features:
#### `@babel/polyfill`[⬆](#index)
[`@babel/polyfill`](https://babeljs.io/docs/usage/polyfill) [**IS** just the import of stable `core-js` features and `regenerator-runtime`](https://github.com/babel/babel/blob/c8bb4500326700e7dc68ce8c4b90b6482c48d82f/packages/babel-polyfill/src/index.js) for generators and async functions, so loading `@babel/polyfill` means loading the global version of `core-js` without ES proposals.
Now it's deprecated in favor of separate inclusion of required parts of `core-js` and `regenerator-runtime` and, for backward compatibility, `@babel/polyfill` is still based on `core-js@2`.
As a full equal of `@babel/polyfill`, you can use the following:
```js
import 'core-js/stable';
import 'regenerator-runtime/runtime';
```
#### `@babel/preset-env`[⬆](#index)
[`@babel/preset-env`](https://github.com/babel/babel/tree/master/packages/babel-preset-env) has `useBuiltIns` option, which optimizes the use of the global version of `core-js`. With `useBuiltIns` option, you should also set `corejs` option to the used version of `core-js`, like `corejs: '3.49'`.
> [!IMPORTANT]
> It is recommended to specify the used minor `core-js` version, like `corejs: '3.49'`, 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/full/set/map';
```
with `chrome 71` target you will have as the 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:
let set = new Set([1, 2, 3]);
```
```js
// second file:
let array = Array.of(1, 2, 3);
```
if the 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]);
```
```js
// second file:
import 'core-js/modules/es.array.of';
var array = Array.of(1, 2, 3);
```
By default, `@babel/preset-env` with `useBuiltIns: 'usage'` option only polyfills stable features, but you can enable polyfilling of proposals by the `proposals` option, as `corejs: { version: '3.49', proposals: true }`.
> [!IMPORTANT]
> In the case of `useBuiltIns: 'usage'`, you should not add `core-js` imports by yourself, they will be added automatically.
#### `@babel/runtime`[⬆](#index)
[`@babel/runtime`](https://babeljs.io/docs/plugins/transform-runtime/) with `corejs: 3` option simplifies work with the `core-js-pure`. It automatically replaces the usage of modern features from the JS standard library to imports from the version of `core-js` without global namespace pollution, so instead of:
```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.
### swc[⬆](#index)
Fast JavaScript transpiler `swc` [contains integration with `core-js`](https://swc.rs/docs/configuration/supported-browsers), that optimizes work with the global version of `core-js`. [Like `@babel/preset-env`](#babelpreset-env), it has 2 modes: `usage` and `entry`, but `usage` mode still works not so well as in `babel`. Example of configuration in `.swcrc`:
```json
{
"env": {
"targets": "> 0.25%, not dead",
"mode": "entry",
"coreJs": "3.49"
}
}
```
### Configurable level of aggressiveness[⬆](#index)
By default, `core-js` sets polyfills only when they are required. That means that `core-js` checks if a feature is available and works correctly or not and if it has no problems, `core-js` uses native implementation.
But sometimes `core-js` feature detection could be too strict for your case. For example, `Promise` constructor requires the support of unhandled rejection tracking and `@@species`.
Sometimes we could have an inverse problem - a knowingly broken environment with problems not covered by `core-js` feature detection.
For those cases, we could redefine this behavior for certain polyfills:
```js
const configurator = require('core-js/configurator');
configurator({
useNative: ['Promise'], // polyfills will be used only if natives are completely unavailable
usePolyfill: ['Array.from', 'String.prototype.padEnd'], // polyfills will be used anyway
useFeatureDetection: ['Map', 'Set'], // default behavior
});
require('core-js/actual');
```
It does not work with some features. Also, if you change the default behavior, even `core-js` internals may not work correctly.
### Custom build[⬆](#index)
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`](/packages/core-js-builder) package for that.
## Supported engines and compatibility data[⬆](#index)
`core-js` tries to support all possible JS engines and environments with ES3 support. Some features have a higher lower bar - for example, *some* accessors can properly work only from ES5, promises require a way to set a microtask or a task, etc.
However, I have no possibility to test `core-js` absolutely everywhere - for example, testing in IE7- and some other ancient was stopped. The list of definitely supported engines you can see in the compatibility table by the link below. [Write](https://github.com/zloirock/core-js/issues) if you have issues or questions with the support of any engine.
`core-js` project provides (as [`core-js-compat`](/packages/core-js-compat) package) all required data about the necessity of `core-js` modules, entry points, and tools for work with it - it's useful for integration with tools like `babel` or `swc`. If you wanna help, you could take a look at the related section of [`CONTRIBUTING.md`](/CONTRIBUTING.md#how-to-update-core-js-compat-data). The visualization of compatibility data and the browser tests runner is available [here](http://zloirock.github.io/core-js/master/compat/), the example:
## Features:[⬆](#index)
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)
```
### ECMAScript[⬆](#index)
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es
```
#### ECMAScript: Object[⬆](#index)
Modules [`es.object.assign`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.assign.js), [`es.object.create`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.create.js), [`es.object.define-getter`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.define-getter.js), [`es.object.define-property`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.define-property.js), [`es.object.define-properties`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.define-properties.js), [`es.object.define-setter`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.define-setter.js), [`es.object.entries`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.entries.js), [`es.object.freeze`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.freeze.js), [`es.object.from-entries`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.from-entries.js), [`es.object.get-own-property-descriptor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.get-own-property-descriptor.js), [`es.object.get-own-property-descriptors`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.get-own-property-descriptors.js), [`es.object.get-own-property-names`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.get-own-property-names.js), [`es.object.get-prototype-of`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.get-prototype-of.js), [`es.object.group-by`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.group-by.js), [`es.object.has-own`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.has-own.js), [`es.object.is`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.is.js), [`es.object.is-extensible`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.is-extensible.js), [`es.object.is-frozen`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.is-frozen.js), [`es.object.is-sealed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.is-sealed.js), [`es.object.keys`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.keys.js), [`es.object.lookup-setter`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.lookup-setter.js), [`es.object.lookup-getter`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.lookup-getter.js), [`es.object.prevent-extensions`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.prevent-extensions.js), [`es.object.proto`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.proto.js), [`es.object.to-string`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.to-string.js), [`es.object.seal`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.seal.js), [`es.object.set-prototype-of`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.set-prototype-of.js), [`es.object.values`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.object.values.js).
```ts
class Object {
toString(): string; // ES2015+ fix: @@toStringTag support
__defineGetter__(property: PropertyKey, getter: Function): void;
__defineSetter__(property: PropertyKey, setter: Function): void;
__lookupGetter__(property: PropertyKey): Function | void;
__lookupSetter__(property: PropertyKey): Function | void;
__proto__: Object | null; // required a way setting of prototype - will not in IE10-, it's for modern engines like Deno
static assign(target: Object, ...sources: Array): Object;
static create(prototype: Object | null, properties?: { [property: PropertyKey]: PropertyDescriptor }): Object;
static defineProperties(object: Object, properties: { [property: PropertyKey]: PropertyDescriptor })): Object;
static defineProperty(object: Object, property: PropertyKey, attributes: PropertyDescriptor): Object;
static entries(object: Object): Array<[string, mixed]>;
static freeze(object: any): any;
static fromEntries(iterable: Iterable<[key, value]>): Object;
static getOwnPropertyDescriptor(object: any, property: PropertyKey): PropertyDescriptor | void;
static getOwnPropertyDescriptors(object: any): { [property: PropertyKey]: PropertyDescriptor };
static getOwnPropertyNames(object: any): Array;
static getPrototypeOf(object: any): Object | null;
static groupBy(items: Iterable, callbackfn: (value: any, index: number) => key): { [key]: Array };
static hasOwn(object: object, key: PropertyKey): boolean;
static is(value1: any, value2: any): boolean;
static isExtensible(object: any): boolean;
static isFrozen(object: any): boolean;
static isSealed(object: any): boolean;
static keys(object: any): Array;
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:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/object
core-js(-pure)/es|stable|actual|full/object/assign
core-js(-pure)/es|stable|actual|full/object/is
core-js(-pure)/es|stable|actual|full/object/set-prototype-of
core-js(-pure)/es|stable|actual|full/object/get-prototype-of
core-js(-pure)/es|stable|actual|full/object/create
core-js(-pure)/es|stable|actual|full/object/define-property
core-js(-pure)/es|stable|actual|full/object/define-properties
core-js(-pure)/es|stable|actual|full/object/get-own-property-descriptor
core-js(-pure)/es|stable|actual|full/object/get-own-property-descriptors
core-js(-pure)/es|stable|actual|full/object/group-by
core-js(-pure)/es|stable|actual|full/object/has-own
core-js(-pure)/es|stable|actual|full/object/keys
core-js(-pure)/es|stable|actual|full/object/values
core-js(-pure)/es|stable|actual|full/object/entries
core-js(-pure)/es|stable|actual|full/object/get-own-property-names
core-js(-pure)/es|stable|actual|full/object/freeze
core-js(-pure)/es|stable|actual|full/object/from-entries
core-js(-pure)/es|stable|actual|full/object/seal
core-js(-pure)/es|stable|actual|full/object/prevent-extensions
core-js/es|stable|actual|full/object/proto
core-js(-pure)/es|stable|actual|full/object/is-frozen
core-js(-pure)/es|stable|actual|full/object/is-sealed
core-js(-pure)/es|stable|actual|full/object/is-extensible
core-js/es|stable|actual|full/object/to-string
core-js(-pure)/es|stable|actual|full/object/define-getter
core-js(-pure)/es|stable|actual|full/object/define-setter
core-js(-pure)/es|stable|actual|full/object/lookup-getter
core-js(-pure)/es|stable|actual|full/object/lookup-setter
```
*Examples*:
```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() { /* empty */ }
function Child() { /* empty */ }
Object.setPrototypeOf(Child.prototype, Parent.prototype);
new Child() instanceof Child; // => true
new Child() instanceof Parent; // => true
({
[Symbol.toStringTag]: 'Foo',
}).toString(); // => '[object Foo]'
Object.keys('qwe'); // => ['0', '1', '2']
Object.getPrototypeOf('qwe') === String.prototype; // => true
Object.values({ a: 1, b: 2, c: 3 }); // => [1, 2, 3]
Object.entries({ a: 1, b: 2, c: 3 }); // => [['a', 1], ['b', 2], ['c', 3]]
for (let [key, value] of Object.entries({ a: 1, b: 2, c: 3 })) {
console.log(key); // => 'a', 'b', 'c'
console.log(value); // => 1, 2, 3
}
// Shallow object cloning with prototype and descriptors:
let copy = Object.create(Object.getPrototypeOf(object), Object.getOwnPropertyDescriptors(object));
// Mixin:
Object.defineProperties(target, Object.getOwnPropertyDescriptors(source));
const map = new Map([['a', 1], ['b', 2]]);
Object.fromEntries(map); // => { a: 1, b: 2 }
class Unit {
constructor(id) {
this.id = id;
}
toString() {
return `unit${ this.id }`;
}
}
const units = new Set([new Unit(101), new Unit(102)]);
Object.fromEntries(units.entries()); // => { unit101: Unit { id: 101 }, unit102: Unit { id: 102 } }
Object.hasOwn({ foo: 42 }, 'foo'); // => true
Object.hasOwn({ foo: 42 }, 'bar'); // => false
Object.hasOwn({}, 'toString'); // => false
Object.groupBy([1, 2, 3, 4, 5], it => it % 2); // => { 1: [1, 3, 5], 0: [2, 4] }
```
#### ECMAScript: Function[⬆](#index)
Modules [`es.function.name`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.function.name.js), [`es.function.has-instance`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.function.has-instance.js). Just ES5: [`es.function.bind`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.function.bind.js).
```ts
class Function {
name: string;
bind(thisArg: any, ...args: Array): Function;
@@hasInstance(value: any): boolean;
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js/es|stable|actual|full/function
core-js/es|stable|actual|full/function/name
core-js/es|stable|actual|full/function/has-instance
core-js(-pure)/es|stable|actual|full/function/bind
core-js(-pure)/es|stable|actual|full/function/virtual/bind
```
[*Example*](https://tinyurl.com/22na9nbm):
```js
(function foo() { /* empty */ }).name; // => 'foo'
console.log.bind(console, 42)(43); // => 42 43
```
#### ECMAScript: Error[⬆](#index)
Modules [`es.aggregate-error`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.aggregate-error.js), [`es.aggregate-error.cause`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.aggregate-error.cause.js), [`es.error.cause`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.error.cause.js), [`es.error.is-error`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.error.is-error.js), [`es.suppressed-error.constructor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.suppressed-error.constructor.js), [`es.error.to-string`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.error.to-string.js).
```ts
class Error {
static isError(value: any): boolean;
constructor(message: string, { cause: any }): %Error%;
toString(): string; // different fixes
}
class [
EvalError,
RangeError,
ReferenceError,
SyntaxError,
TypeError,
URIError,
WebAssembly.CompileError,
WebAssembly.LinkError,
WebAssembly.RuntimeError,
] extends Error {
constructor(message: string, { cause: any }): %Error%;
}
class AggregateError extends Error {
constructor(errors: Iterable, message?: string, { cause: any }?): AggregateError;
errors: Array;
message: string;
cause: any;
}
class SuppressedError extends Error {
constructor(error: any, suppressed: any, message?: string): SuppressedError;
error: any;
suppressed: any;
message: string;
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js/es|stable|actual|full/error
core-js/es|stable|actual|full/error/constructor
core-js(-pure)/es|stable|actual|full/error/is-error
core-js/es|stable|actual|full/error/to-string
core-js(-pure)/es|stable|actual|full/aggregate-error
core-js(-pure)/es|stable|actual|full/suppressed-error
```
[*Example*](https://is.gd/1SufcH):
```js
const error1 = new TypeError('Error 1');
const error2 = new TypeError('Error 2');
const aggregate = new AggregateError([error1, error2], 'Collected errors');
aggregate.errors[0] === error1; // => true
aggregate.errors[1] === error2; // => true
const cause = new TypeError('Something wrong');
const error = new TypeError('Here explained what`s wrong', { cause });
error.cause === cause; // => true
Error.prototype.toString.call({ message: 1, name: 2 }) === '2: 1'; // => true
```
[*Example*](https://tinyurl.com/23nauwoz):
```js
Error.isError(new Error('error')); // => true
Error.isError(new TypeError('error')); // => true
Error.isError(new DOMException('error')); // => true
Error.isError(null); // => false
Error.isError({}); // => false
Error.isError(Object.create(Error.prototype)); // => false
```
> [!WARNING]
> We have no bulletproof way to polyfill this `Error.isError` / check if the object is an error, so it's an enough naive implementation.
#### ECMAScript: Array[⬆](#index)
Modules [`es.array.from`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.from.js), [`es.array.from-async`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.from-async.js), [`es.array.is-array`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.is-array.js), [`es.array.of`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.of.js), [`es.array.copy-within`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.copy-within.js), [`es.array.fill`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.fill.js), [`es.array.find`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.find.js), [`es.array.find-index`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.find-index.js), [`es.array.find-last`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.find-last.js), [`es.array.find-last-index`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.find-last-index.js), [`es.array.iterator`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.iterator.js), [`es.array.includes`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.includes.js), [`es.array.push`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.push.js), [`es.array.slice`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.slice.js), [`es.array.join`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.join.js), [`es.array.unshift`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.unshift.js), [`es.array.index-of`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.index-of.js), [`es.array.last-index-of`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.last-index-of.js), [`es.array.every`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.every.js), [`es.array.some`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.some.js), [`es.array.for-each`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.for-each.js), [`es.array.map`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.map.js), [`es.array.filter`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.filter.js), [`es.array.reduce`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.reduce.js), [`es.array.reduce-right`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.reduce-right.js), [`es.array.reverse`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.reverse.js), [`es.array.sort`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.sort.js), [`es.array.flat`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.flat.js), [`es.array.flat-map`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.flat-map.js), [`es.array.unscopables.flat`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.unscopables.flat.js), [`es.array.unscopables.flat-map`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.unscopables.flat-map.js), [`es.array.at`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.at.js), [`es.array.to-reversed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.to-reversed.js), [`es.array.to-sorted`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.to-sorted.js), [`es.array.to-spliced`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.to-spliced.js), [`es.array.with`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.array.with.js).
```ts
class Array {
at(index: int): any;
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): uint;
findLast(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): any;
findLastIndex(callbackfn: (value: any, index: number, target: any) => boolean, thisArg?: any): uint;
flat(depthArg?: number = 1): Array;
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
push(...args: Array): uint;
reduce(callbackfn: (memo: any, value: any, index: number, target: any) => any, initialValue?: any): any;
reduceRight(callbackfn: (memo: any, value: any, index: number, target: any) => any, initialValue?: any): any;
reverse(): this; // Safari 12.0 bug fix
slice(start?: number, end?: number): Array; // 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; // with modern behavior like stable sort
toReversed(): Array;
toSpliced(start?: number, deleteCount?: number, ...items: Array): Array;
toSorted(comparefn?: (a: any, b: any) => number): Array;
unshift(...args: Array): uint;
values(): Iterator;
with(index: includes, value: any): Array;
@@iterator(): Iterator;
@@unscopables: { [newMethodNames: string]: true };
static from(items: Iterable | ArrayLike, mapFn?: (value: any, index: number) => any, thisArg?: any): Array;
static fromAsync(asyncItems: AsyncIterable | 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|actual|full/array
core-js(-pure)/es|stable|actual|full/array/from
core-js(-pure)/es|stable|actual|full/array/from-async
core-js(-pure)/es|stable|actual|full/array/of
core-js(-pure)/es|stable|actual|full/array/is-array
core-js(-pure)/es|stable|actual|full/array(/virtual)/at
core-js(-pure)/es|stable|actual|full/array(/virtual)/concat
core-js(-pure)/es|stable|actual|full/array(/virtual)/copy-within
core-js(-pure)/es|stable|actual|full/array(/virtual)/entries
core-js(-pure)/es|stable|actual|full/array(/virtual)/every
core-js(-pure)/es|stable|actual|full/array(/virtual)/fill
core-js(-pure)/es|stable|actual|full/array(/virtual)/filter
core-js(-pure)/es|stable|actual|full/array(/virtual)/find
core-js(-pure)/es|stable|actual|full/array(/virtual)/find-index
core-js(-pure)/es|stable|actual|full/array(/virtual)/find-last
core-js(-pure)/es|stable|actual|full/array(/virtual)/find-last-index
core-js(-pure)/es|stable|actual|full/array(/virtual)/flat
core-js(-pure)/es|stable|actual|full/array(/virtual)/flat-map
core-js(-pure)/es|stable|actual|full/array(/virtual)/for-each
core-js(-pure)/es|stable|actual|full/array(/virtual)/includes
core-js(-pure)/es|stable|actual|full/array(/virtual)/index-of
core-js(-pure)/es|stable|actual|full/array(/virtual)/iterator
core-js(-pure)/es|stable|actual|full/array(/virtual)/join
core-js(-pure)/es|stable|actual|full/array(/virtual)/keys
core-js(-pure)/es|stable|actual|full/array(/virtual)/last-index-of
core-js(-pure)/es|stable|actual|full/array(/virtual)/map
core-js(-pure)/es|stable|actual|full/array(/virtual)/push
core-js(-pure)/es|stable|actual|full/array(/virtual)/reduce
core-js(-pure)/es|stable|actual|full/array(/virtual)/reduce-right
core-js(-pure)/es|stable|actual|full/array(/virtual)/reverse
core-js(-pure)/es|stable|actual|full/array(/virtual)/slice
core-js(-pure)/es|stable|actual|full/array(/virtual)/some
core-js(-pure)/es|stable|actual|full/array(/virtual)/sort
core-js(-pure)/es|stable|actual|full/array(/virtual)/splice
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-reversed
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-sorted
core-js(-pure)/es|stable|actual|full/array(/virtual)/to-spliced
core-js(-pure)/es|stable|actual|full/array(/virtual)/unshift
core-js(-pure)/es|stable|actual|full/array(/virtual)/values
core-js(-pure)/es|stable|actual|full/array(/virtual)/with
```
[*Examples*](https://tinyurl.com/2oaa8x2x):
```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 ** 2); // => [1, 4, 9]
Array.of(1); // => [1]
Array.of(1, 2, 3); // => [1, 2, 3]
let array = ['a', 'b', 'c'];
for (let value of array) console.log(value); // => 'a', 'b', 'c'
for (let value of array.values()) console.log(value); // => 'a', 'b', 'c'
for (let key of array.keys()) console.log(key); // => 0, 1, 2
for (let [key, value] of array.entries()) {
console.log(key); // => 0, 1, 2
console.log(value); // => 'a', 'b', 'c'
}
function isOdd(value) {
return value % 2;
}
[4, 8, 15, 16, 23, 42].find(isOdd); // => 15
[4, 8, 15, 16, 23, 42].findIndex(isOdd); // => 2
[1, 2, 3, 4].findLast(isOdd); // => 3
[1, 2, 3, 4].findLastIndex(isOdd); // => 2
Array(5).fill(42); // => [42, 42, 42, 42, 42]
[1, 2, 3, 4, 5].copyWithin(0, 3); // => [4, 5, 3, 4, 5]
[1, 2, 3].includes(2); // => true
[1, 2, 3].includes(4); // => false
[1, 2, 3].includes(2, 2); // => false
[NaN].indexOf(NaN); // => -1
[NaN].includes(NaN); // => true
Array(1).indexOf(undefined); // => -1
Array(1).includes(undefined); // => true
[1, [2, 3], [4, 5]].flat(); // => [1, 2, 3, 4, 5]
[1, [2, [3, [4]]], 5].flat(); // => [1, 2, [3, [4]], 5]
[1, [2, [3, [4]]], 5].flat(3); // => [1, 2, 3, 4, 5]
[{ a: 1, b: 2 }, { a: 3, b: 4 }, { a: 5, b: 6 }].flatMap(it => [it.a, it.b]); // => [1, 2, 3, 4, 5, 6]
[1, 2, 3].at(1); // => 2
[1, 2, 3].at(-1); // => 3
const sequence = [1, 2, 3];
sequence.toReversed(); // => [3, 2, 1]
sequence; // => [1, 2, 3]
const initialArray = [1, 2, 3, 4];
initialArray.toSpliced(1, 2, 5, 6, 7); // => [1, 5, 6, 7, 4]
initialArray; // => [1, 2, 3, 4]
const outOfOrder = [3, 1, 2];
outOfOrder.toSorted(); // => [1, 2, 3]
outOfOrder; // => [3, 1, 2]
const correctionNeeded = [1, 1, 3];
correctionNeeded.with(1, 2); // => [1, 2, 3]
correctionNeeded; // => [1, 1, 3]
```
[*`Array.fromAsync` example*](https://tinyurl.com/2bt9bhwn):
```js
await Array.fromAsync((async function * () { yield * [1, 2, 3]; })(), i => i ** 2); // => [1, 4, 9]
```
#### ECMAScript: Iterator[⬆](#index)
Modules [`es.iterator.constructor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.constructor.js), [`es.iterator.concat`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.concat.js), [`es.iterator.dispose`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.dispose.js), [`es.iterator.drop`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.drop.js), [`es.iterator.every`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.every.js), [`es.iterator.filter`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.filter.js), [`es.iterator.find`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.find.js), [`es.iterator.flat-map`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.flat-map.js), [`es.iterator.for-each`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.for-each.js), [`es.iterator.from`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.from.js), [`es.iterator.map`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.map.js), [`es.iterator.reduce`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.reduce.js), [`es.iterator.some`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.some.js), [`es.iterator.take`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.take.js), [`es.iterator.to-array`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.iterator.to-array.js)
```ts
class Iterator {
static concat(...items: Array): Iterator;
static from(iterable: Iterable | Iterator): Iterator;
drop(limit: uint): Iterator;
every(callbackfn: (value: any, counter: uint) => boolean): boolean;
filter(callbackfn: (value: any, counter: uint) => boolean): Iterator;
find(callbackfn: (value: any, counter: uint) => boolean)): any;
flatMap(callbackfn: (value: any, counter: uint) => Iterable | Iterator): Iterator;
forEach(callbackfn: (value: any, counter: uint) => void): void;
map(callbackfn: (value: any, counter: uint) => any): Iterator;
reduce(callbackfn: (memo: any, value: any, counter: uint) => any, initialValue: any): any;
some(callbackfn: (value: any, counter: uint) => boolean): boolean;
take(limit: uint): Iterator;
toArray(): Array;
@@dispose(): undefined;
@@toStringTag: 'Iterator'
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/iterator
core-js(-pure)/es|stable|actual|full/iterator/concat
core-js(-pure)/es|stable|actual|full/iterator/dispose
core-js(-pure)/es|stable|actual|full/iterator/drop
core-js(-pure)/es|stable|actual|full/iterator/every
core-js(-pure)/es|stable|actual|full/iterator/filter
core-js(-pure)/es|stable|actual|full/iterator/find
core-js(-pure)/es|stable|actual|full/iterator/flat-map
core-js(-pure)/es|stable|actual|full/iterator/for-each
core-js(-pure)/es|stable|actual|full/iterator/from
core-js(-pure)/es|stable|actual|full/iterator/map
core-js(-pure)/es|stable|actual|full/iterator/reduce
core-js(-pure)/es|stable|actual|full/iterator/some
core-js(-pure)/es|stable|actual|full/iterator/take
core-js(-pure)/es|stable|actual|full/iterator/to-array
```
[Examples](https://tinyurl.com/24af2z7v):
```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() > 0.9, value: Math.random() * 10 | 0 }),
}).toArray(); // => [7, 6, 3, 0, 2, 8]
Iterator.concat([0, 1].values(), [2, 3], function * () {
yield 4;
yield 5;
}()).toArray(); // => [0, 1, 2, 3, 4, 5]
```
> [!WARNING]
> - For preventing prototype pollution, in the `pure` version, new `%IteratorPrototype%` methods are not added to the real `%IteratorPrototype%`, they are available only on wrappers - instead of `[].values().map(fn)` use `Iterator.from([]).map(fn)`.
#### ECMAScript: String and RegExp[⬆](#index)
The main part of `String` features: modules [`es.string.from-code-point`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.from-code-point.js), [`es.string.raw`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.raw.js), [`es.string.iterator`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.iterator.js), [`es.string.split`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.split.js), [`es.string.code-point-at`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.code-point-at.js), [`es.string.ends-with`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.ends-with.js), [`es.string.includes`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.includes.js), [`es.string.repeat`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.repeat.js), [`es.string.pad-start`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.pad-start.js), [`es.string.pad-end`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.pad-end.js), [`es.string.starts-with`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.starts-with.js), [`es.string.trim`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.trim.js), [`es.string.trim-start`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.trim-start.js), [`es.string.trim-end`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.trim-end.js), [`es.string.match-all`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.match-all.js), [`es.string.replace-all`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.replace-all.js), [`es.string.at-alternative`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.at-alternative.js), [`es.string.is-well-formed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.is-well-formed.js), [`es.string.to-well-formed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.to-well-formed.js).
Adding support of well-known [symbols](#ecmascript-symbol) `@@match`, `@@replace`, `@@search` and `@@split` and direct `.exec` calls to related `String` methods, modules [`es.string.match`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.match.js), [`es.string.replace`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.replace.js), [`es.string.search`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.search.js) and [`es.string.split`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.split.js).
Annex B methods. Modules [`es.string.anchor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.anchor.js), [`es.string.big`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.big.js), [`es.string.blink`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.blink.js), [`es.string.bold`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.bold.js), [`es.string.fixed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.fixed.js), [`es.string.fontcolor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.fontcolor.js), [`es.string.fontsize`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.fontsize.js), [`es.string.italics`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.italics.js), [`es.string.link`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.link.js), [`es.string.small`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.small.js), [`es.string.strike`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.strike.js), [`es.string.sub`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.sub.js), [`es.string.sup`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.sup.js), [`es.string.substr`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.string.substr.js), [`es.escape`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.escape.js) and [`es.unescape`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.unescape.js).
`RegExp` features: modules [`es.regexp.constructor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.regexp.constructor.js), [`es.regexp.escape`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.regexp.escape.js), [`es.regexp.dot-all`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.regexp.dot-all.js), [`es.regexp.flags`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.regexp.flags.js), [`es.regexp.sticky`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.regexp.sticky.js) and [`es.regexp.test`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.regexp.test.js).
```ts
class String {
static fromCodePoint(...codePoints: Array): string;
static raw({ raw: Array }, ...substitutions: Array): string;
at(index: int): string;
includes(searchString: string, position?: number): boolean;
startsWith(searchString: string, position?: number): boolean;
endsWith(searchString: string, position?: number): boolean;
repeat(count: number): string;
padStart(length: number, fillStr?: string = ' '): string;
padEnd(length: number, fillStr?: string = ' '): string;
codePointAt(pos: number): number | void;
match(template: any): any; // ES2015+ fix for support @@match
matchAll(regexp: RegExp): Iterator;
replace(template: any, replacer: any): any; // ES2015+ fix for support @@replace
replaceAll(searchValue: string | RegExp, replaceString: string | (searchValue, index, this) => string): string;
search(template: any): any; // ES2015+ fix for support @@search
split(template: any, limit?: int): Array;; // ES2015+ fix for support @@split, some fixes for old engines
trim(): string;
trimLeft(): string;
trimRight(): string;
trimStart(): string;
trimEnd(): string;
isWellFormed(): boolean;
toWellFormed(): string;
anchor(name: string): string;
big(): string;
blink(): string;
bold(): string;
fixed(): string;
fontcolor(color: string): string;
fontsize(size: any): string;
italics(): string;
link(url: string): string;
small(): string;
strike(): string;
sub(): string;
substr(start: int, length?: int): string;
sup(): string;
@@iterator(): Iterator;
}
class RegExp {
// support of sticky (`y`) flag, dotAll (`s`) flag, named capture groups, can alter flags
constructor(pattern: RegExp | string, flags?: string): RegExp;
static escape(value: string): string
exec(): Array | null; // IE8 fixes
test(string: string): boolean; // delegation to `.exec`
toString(): string; // ES2015+ fix - generic
@@match(string: string): Array | null;
@@matchAll(string: string): Iterator;
@@replace(string: string, replaceValue: Function | string): string;
@@search(string: string): number;
@@split(string: string, limit: number): Array;
readonly attribute dotAll: boolean; // IE9+
readonly attribute flags: string; // IE9+
readonly attribute sticky: boolean; // IE9+
}
function escape(string: string): string;
function unescape(string: string): string;
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/string
core-js(-pure)/es|stable|actual|full/string/from-code-point
core-js(-pure)/es|stable|actual|full/string/raw
core-js/es|stable|actual|full/string/match
core-js/es|stable|actual|full/string/replace
core-js/es|stable|actual|full/string/search
core-js/es|stable|actual|full/string/split
core-js(-pure)/es|stable|actual/string(/virtual)/at
core-js(-pure)/es|stable|actual|full/string(/virtual)/code-point-at
core-js(-pure)/es|stable|actual|full/string(/virtual)/ends-with
core-js(-pure)/es|stable|actual|full/string(/virtual)/includes
core-js(-pure)/es|stable|actual|full/string(/virtual)/starts-with
core-js(-pure)/es|stable|actual|full/string(/virtual)/match-all
core-js(-pure)/es|stable|actual|full/string(/virtual)/pad-start
core-js(-pure)/es|stable|actual|full/string(/virtual)/pad-end
core-js(-pure)/es|stable|actual|full/string(/virtual)/repeat
core-js(-pure)/es|stable|actual|full/string(/virtual)/replace-all
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-start
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-end
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-left
core-js(-pure)/es|stable|actual|full/string(/virtual)/trim-right
core-js(-pure)/es|stable|actual|full/string(/virtual)/is-well-formed
core-js(-pure)/es|stable|actual|full/string(/virtual)/to-well-formed
core-js(-pure)/es|stable|actual|full/string(/virtual)/anchor
core-js(-pure)/es|stable|actual|full/string(/virtual)/big
core-js(-pure)/es|stable|actual|full/string(/virtual)/blink
core-js(-pure)/es|stable|actual|full/string(/virtual)/bold
core-js(-pure)/es|stable|actual|full/string(/virtual)/fixed
core-js(-pure)/es|stable|actual|full/string(/virtual)/fontcolor
core-js(-pure)/es|stable|actual|full/string(/virtual)/fontsize
core-js(-pure)/es|stable|actual|full/string(/virtual)/italics
core-js(-pure)/es|stable|actual|full/string(/virtual)/link
core-js(-pure)/es|stable|actual|full/string(/virtual)/small
core-js(-pure)/es|stable|actual|full/string(/virtual)/strike
core-js(-pure)/es|stable|actual|full/string(/virtual)/sub
core-js(-pure)/es|stable|actual|full/string(/virtual)/substr
core-js(-pure)/es|stable|actual|full/string(/virtual)/sup
core-js(-pure)/es|stable|actual|full/string(/virtual)/iterator
core-js/es|stable|actual|full/regexp
core-js/es|stable|actual|full/regexp/constructor
core-js(-pure)/es|stable|actual|full/regexp/escape
core-js/es|stable|actual|full/regexp/dot-all
core-js(-pure)/es|stable|actual|full/regexp/flags
core-js/es|stable|actual|full/regexp/sticky
core-js/es|stable|actual|full/regexp/test
core-js/es|stable|actual|full/regexp/to-string
core-js/es|stable|actual|full/escape
core-js/es|stable|actual|full/unescape
```
[*Examples*](https://tinyurl.com/22uafm3p):
```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('https://example.com'); // => 'baz'
RegExp('.', 's').test('\n'); // => true
RegExp('.', 's').dotAll; // => true
RegExp('foo:(?\\w+),bar:(?\\w+)').exec('foo:abc,bar:def').groups; // => { foo: 'abc', bar: 'def' }
'foo:abc,bar:def'.replace(RegExp('foo:(?\\w+),bar:(?\\w+)'), '$,$'); // => 'def,abc'
// eslint-disable-next-line regexp/no-useless-flag -- example
RegExp(/./g, 'm'); // => /./m
/foo/.flags; // => ''
/foo/gi.flags; // => 'gi'
RegExp('foo', 'y').sticky; // => true
const text = 'First line\nSecond line';
const regex = RegExp('(?\\S+) line\\n?', 'y');
regex.exec(text).groups.index; // => 'First'
regex.exec(text).groups.index; // => 'Second'
regex.exec(text); // => null
'foo'.match({ [Symbol.match]: () => 1 }); // => 1
'foo'.replace({ [Symbol.replace]: () => 2 }); // => 2
'foo'.search({ [Symbol.search]: () => 3 }); // => 3
'foo'.split({ [Symbol.split]: () => 4 }); // => 4
RegExp.prototype.toString.call({ source: 'foo', flags: 'bar' }); // => '/foo/bar'
' hello '.trimLeft(); // => 'hello '
' hello '.trimRight(); // => ' hello'
' hello '.trimStart(); // => 'hello '
' hello '.trimEnd(); // => ' hello'
for (let { groups: { number, letter } } of '1111a2b3cccc'.matchAll(RegExp('(?\\d)(?\\D)', 'g'))) {
console.log(number, letter); // => 1 a, 2 b, 3 c
}
'Test abc test test abc test.'.replaceAll('abc', 'foo'); // -> 'Test foo test test foo test.'
'abc'.at(1); // => 'b'
'abc'.at(-1); // => 'c'
'a💩b'.isWellFormed(); // => true
'a\uD83Db'.isWellFormed(); // => false
'a💩b'.toWellFormed(); // => 'a💩b'
'a\uD83Db'.toWellFormed(); // => 'a�b'
```
[*Example*](https://tinyurl.com/ykac4qgy):
```js
console.log(RegExp.escape('10$')); // => '\\x310\\$'
console.log(RegExp.escape('abcdefg_123456')); // => '\\x61bcdefg_123456'
console.log(RegExp.escape('Привет')); // => 'Привет'
console.log(RegExp.escape('(){}[]|,.?*+-^$=<>\\/#&!%:;@~\'"`'));
// => '\\(\\)\\{\\}\\[\\]\\|\\x2c\\.\\?\\*\\+\\x2d\\^\\$\\x3d\\x3c\\x3e\\\\\\/\\x23\\x26\\x21\\x25\\x3a\\x3b\\x40\\x7e\\x27\\x22\\x60'
console.log(RegExp.escape('\u0009\u000A\u000B\u000C\u000D\u0020\u00A0\u1680\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028\u2029\uFEFF'));
// => '\\\t\\\n\\\v\\\f\\\r\\x20\\xa0\\u1680\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u202f\\u205f\\u3000\\u2028\\u2029\\ufeff'
console.log(RegExp.escape('💩')); // => '💩'
console.log(RegExp.escape('\uD83D')); // => '\\ud83d'
```
#### ECMAScript: Number[⬆](#index)
Module [`es.number.constructor`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.constructor.js). `Number` constructor support binary and octal literals, [*example*](https://tinyurl.com/2659klkj):
```js
Number('0b1010101'); // => 85
Number('0o7654321'); // => 2054353
```
Modules [`es.number.epsilon`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.epsilon.js), [`es.number.is-finite`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.is-finite.js), [`es.number.is-integer`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.is-integer.js), [`es.number.is-nan`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.is-nan.js), [`es.number.is-safe-integer`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.is-safe-integer.js), [`es.number.max-safe-integer`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.max-safe-integer.js), [`es.number.min-safe-integer`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.min-safe-integer.js), [`es.number.parse-float`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.parse-float.js), [`es.number.parse-int`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.parse-int.js), [`es.number.to-exponential`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.to-exponential.js), [`es.number.to-fixed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.to-fixed.js), [`es.number.to-precision`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.number.to-precision.js), [`es.parse-int`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.parse-int.js), [`es.parse-float`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.parse-float.js).
```ts
class Number {
constructor(value: any): number;
toExponential(digits: number): string;
toFixed(digits: number): string;
toPrecision(precision: number): string;
static isFinite(number: any): boolean;
static isNaN(number: any): boolean;
static isInteger(number: any): boolean;
static isSafeInteger(number: any): boolean;
static parseFloat(string: string): number;
static parseInt(string: string, radix?: number = 10): number;
static EPSILON: number;
static MAX_SAFE_INTEGER: number;
static MIN_SAFE_INTEGER: number;
}
function parseFloat(string: string): number;
function parseInt(string: string, radix?: number = 10): number;
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/number
core-js(-pure)/es|stable|actual|full/number/constructor
core-js(-pure)/es|stable|actual|full/number/is-finite
core-js(-pure)/es|stable|actual|full/number/is-nan
core-js(-pure)/es|stable|actual|full/number/is-integer
core-js(-pure)/es|stable|actual|full/number/is-safe-integer
core-js(-pure)/es|stable|actual|full/number/parse-float
core-js(-pure)/es|stable|actual|full/number/parse-int
core-js(-pure)/es|stable|actual|full/number/epsilon
core-js(-pure)/es|stable|actual|full/number/max-safe-integer
core-js(-pure)/es|stable|actual|full/number/min-safe-integer
core-js(-pure)/es|stable|actual|full/number(/virtual)/to-exponential
core-js(-pure)/es|stable|actual|full/number(/virtual)/to-fixed
core-js(-pure)/es|stable|actual|full/number(/virtual)/to-precision
core-js(-pure)/es|stable|actual|full/parse-float
core-js(-pure)/es|stable|actual|full/parse-int
```
#### ECMAScript: Math[⬆](#index)
Modules [`es.math.acosh`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.acosh.js), [`es.math.asinh`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.asinh.js), [`es.math.atanh`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.atanh.js), [`es.math.cbrt`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.cbrt.js), [`es.math.clz32`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.clz32.js), [`es.math.cosh`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.cosh.js), [`es.math.expm1`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.expm1.js), [`es.math.fround`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.fround.js), [`es.math.f16round`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.f16round.js), [`es.math.hypot`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.hypot.js), [`es.math.imul`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.imul.js), [`es.math.log10`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.log10.js), [`es.math.log1p`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.log1p.js), [`es.math.log2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.log2.js), [`es.math.sign`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.sign.js), [`es.math.sinh`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.sinh.js), [`esnext.math.sum-precise`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.math.sum-precise.js), [`es.math.tanh`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.tanh.js), [`es.math.trunc`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.trunc.js).
```ts
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;
f16round(number: any): 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;
sumPrecise(items: Iterable): Number;
tanh(number: number): number;
trunc(number: number): number;
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/math
core-js(-pure)/es|stable|actual|full/math/acosh
core-js(-pure)/es|stable|actual|full/math/asinh
core-js(-pure)/es|stable|actual|full/math/atanh
core-js(-pure)/es|stable|actual|full/math/cbrt
core-js(-pure)/es|stable|actual|full/math/clz32
core-js(-pure)/es|stable|actual|full/math/cosh
core-js(-pure)/es|stable|actual|full/math/expm1
core-js(-pure)/es|stable|actual|full/math/fround
core-js(-pure)/es|stable|actual|full/math/f16round
core-js(-pure)/es|stable|actual|full/math/hypot
core-js(-pure)/es|stable|actual|full/math/imul
core-js(-pure)/es|stable|actual|full/math/log1p
core-js(-pure)/es|stable|actual|full/math/log10
core-js(-pure)/es|stable|actual|full/math/log2
core-js(-pure)/es|stable|actual|full/math/sign
core-js(-pure)/es|stable|actual|full/math/sinh
core-js(-pure)/es|stable|actual|full/math/sum-precise
core-js(-pure)/es|stable|actual|full/math/tanh
core-js(-pure)/es|stable|actual|full/math/trunc
```
[*Examples*](https://tinyurl.com/2bd3nako):
```js
1e20 + 0.1 + -1e20; // => 0
Math.sumPrecise([1e20, 0.1, -1e20]); // => 0.1
```
#### ECMAScript: Date[⬆](#index)
Modules [`es.date.to-string`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.to-string.js), ES5 features with fixes: [`es.date.now`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.now.js), [`es.date.to-iso-string`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.to-iso-string.js), [`es.date.to-json`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.to-json.js) and [`es.date.to-primitive`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.to-primitive.js).
Annex B methods. Modules [`es.date.get-year`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.get-year.js), [`es.date.set-year`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.set-year.js) and [`es.date.to-gmt-string`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.date.to-gmt-string.js).
```ts
class Date {
getYear(): int;
setYear(year: int): number;
toGMTString(): string;
toISOString(): string;
toJSON(): string;
toString(): string;
@@toPrimitive(hint: 'default' | 'number' | 'string'): string | number;
static now(): number;
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js/es|stable|actual|full/date
core-js/es|stable|actual|full/date/to-string
core-js(-pure)/es|stable|actual|full/date/now
core-js(-pure)/es|stable|actual|full/date/get-year
core-js(-pure)/es|stable|actual|full/date/set-year
core-js(-pure)/es|stable|actual|full/date/to-gmt-string
core-js(-pure)/es|stable|actual|full/date/to-iso-string
core-js(-pure)/es|stable|actual|full/date/to-json
core-js(-pure)/es|stable|actual|full/date/to-primitive
```
[*Example*](https://tinyurl.com/2cngq74c):
```js
new Date(NaN).toString(); // => 'Invalid Date'
```
#### ECMAScript: Promise[⬆](#index)
Modules [`es.promise`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.promise.js), [`es.promise.all-settled`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.promise.all-settled.js), [`es.promise.any`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.promise.any.js), [`es.promise.finally`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.promise.finally.js), [`es.promise.try`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.promise.try.js) and [`es.promise.with-resolvers`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.promise.with-resolvers.js).
```ts
class Promise {
constructor(executor: (resolve: Function, reject: Function) => void): Promise;
then(onFulfilled: Function, onRejected: Function): Promise;
catch(onRejected: Function): Promise;
finally(onFinally: Function): Promise;
static all(iterable: Iterable): Promise;
static allSettled(iterable: Iterable): Promise;
static any(promises: Iterable): Promise;
static race(iterable: Iterable): Promise;
static reject(r: any): Promise;
static resolve(x: any): Promise;
static try(callbackfn: Function, ...args?: Array): Promise;
static withResolvers(): { promise: Promise, resolve: function, reject: function };
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/promise
core-js(-pure)/es|stable|actual|full/promise/all-settled
core-js(-pure)/es|stable|actual|full/promise/any
core-js(-pure)/es|stable|actual|full/promise/finally
core-js(-pure)/es|stable|actual|full/promise/try
core-js(-pure)/es|stable|actual|full/promise/with-resolvers
```
Basic [*example*](https://tinyurl.com/23bhbhbu):
```js
/* eslint-disable promise/prefer-await-to-callbacks -- example */
function sleepRandom(time) {
return new Promise((resolve, reject) => {
setTimeout(resolve, time * 1e3, 0 | Math.random() * 1e3);
});
}
console.log('Run'); // => Run
sleepRandom(5).then(result => {
console.log(result); // => 869, after 5 sec.
return sleepRandom(10);
}).then(result => {
console.log(result); // => 202, after 10 sec.
}).then(() => {
console.log('immediately after'); // => immediately after
throw new Error('Irror!');
}).then(() => {
console.log('will not be displayed');
}).catch(error => console.log(error)); // => => Error: Irror!
```
`Promise.resolve` and `Promise.reject` [*example*](https://tinyurl.com/28nq4agd):
```js
/* eslint-disable promise/prefer-await-to-callbacks -- example */
Promise.resolve(42).then(x => console.log(x)); // => 42
Promise.reject(42).catch(error => console.log(error)); // => 42
Promise.resolve($.getJSON('/data.json')); // => ES promise
```
`Promise#finally` [*example*](https://tinyurl.com/2ywzmz72):
```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*](https://tinyurl.com/23nc596a):
```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*](https://tinyurl.com/2degj8ux):
```js
/* eslint-disable promise/prefer-await-to-callbacks -- example */
function timeLimit(promise, time) {
return Promise.race([promise, new Promise((resolve, reject) => {
setTimeout(reject, time * 1e3, new Error(`Await > ${ time } sec`));
})]);
}
timeLimit(sleepRandom(5), 10).then(x => console.log(x)); // => 853, after 5 sec.
timeLimit(sleepRandom(15), 10).catch(error => console.log(error)); // Error: Await > 10 sec
```
`Promise.allSettled` [*example*](https://tinyurl.com/2akj7c2u):
```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://tinyurl.com/23u59v6g):
```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]
```
`Promise.try` [*examples*](https://tinyurl.com/2p48ojau):
```js
/* eslint-disable promise/prefer-await-to-callbacks -- example */
Promise.try(() => 42).then(it => console.log(`Promise, resolved as ${ it }`));
Promise.try(() => { throw new Error('42'); }).catch(error => console.log(`Promise, rejected as ${ error }`));
Promise.try(async () => 42).then(it => console.log(`Promise, resolved as ${ it }`));
Promise.try(async () => { throw new Error('42'); }).catch(error => console.log(`Promise, rejected as ${ error }`));
Promise.try(it => it, 42).then(it => console.log(`Promise, resolved as ${ it }`));
```
`Promise.withResolvers` [*examples*](https://tinyurl.com/2gx4t3xu):
```js
const d = Promise.withResolvers();
d.resolve(42);
d.promise.then(console.log); // => 42
```
[Example](https://tinyurl.com/bde6am73) 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 new Error(msg);
}
(async () => {
try {
console.log('Run'); // => Run
console.log(await sleepRandom(5)); // => 936, after 5 sec.
let [a, b, c] = await Promise.all([
sleepRandom(5),
sleepRandom(15),
sleepRandom(10),
]);
console.log(a, b, c); // => 210 445 71, after 15 sec.
await sleepError(5, 'Error!');
console.log('Will not be displayed');
} catch (error) {
console.log(error); // => Error: 'Error!', after 5 sec.
}
})();
```
##### Unhandled rejection tracking[⬆](#index)
In Node.js, like in native implementation, available events [`unhandledRejection`](https://nodejs.org/api/process.html#process_event_unhandledrejection) and [`rejectionHandled`](https://nodejs.org/api/process.html#process_event_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]
// eslint-disable-next-line promise/prefer-await-to-then -- example
setTimeout(() => promise.catch(() => { /* empty */ }), 1e3);
// handled [object Promise]
```
In a browser on rejection, by default, you will see notify in the console, or you can add a custom handler and a handler on handling unhandled, [*example*](https://tinyurl.com/5n6nj2e8):
```js
globalThis.addEventListener('unhandledrejection', e => console.log('unhandled', e.reason, e.promise));
globalThis.addEventListener('rejectionhandled', e => console.log('handled', e.reason, e.promise));
// or
globalThis.onunhandledrejection = e => console.log('unhandled', e.reason, e.promise);
globalThis.onrejectionhandled = e => console.log('handled', e.reason, e.promise);
let promise = Promise.reject(42);
// => unhandled 42 [object Promise]
// eslint-disable-next-line promise/prefer-await-to-then -- example
setTimeout(() => promise.catch(() => { /* empty */ }), 1e3);
// => handled 42 [object Promise]
```
#### ECMAScript: Symbol[⬆](#index)
Modules [`es.symbol`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.js), [`es.symbol.async-dispose`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.async-dispose.js), [`es.symbol.async-iterator`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.async-iterator.js), [`es.symbol.description`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.description.js), [`es.symbol.dispose`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.dispose.js), [`es.symbol.has-instance`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.has-instance.js), [`es.symbol.is-concat-spreadable`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.is-concat-spreadable.js), [`es.symbol.iterator`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.iterator.js), [`es.symbol.match`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.match.js), [`es.symbol.replace`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.replace.js), [`es.symbol.search`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.search.js), [`es.symbol.species`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.species.js), [`es.symbol.split`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.split.js), [`es.symbol.to-primitive`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.to-primitive.js), [`es.symbol.to-string-tag`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.to-string-tag.js), [`es.symbol.unscopables`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.symbol.unscopables.js), [`es.math.to-string-tag`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.math.to-string-tag.js).
```ts
class Symbol {
constructor(description?): symbol;
readonly attribute description: string | void;
static asyncDispose: @@asyncDispose;
static asyncIterator: @@asyncIterator;
static dispose: @@dispose;
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.
```ts
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|actual|full/symbol
core-js(-pure)/es|stable|actual|full/symbol/async-dispose
core-js(-pure)/es|stable|actual|full/symbol/async-iterator
core-js/es|stable|actual|full/symbol/description
core-js(-pure)/es|stable|actual|full/symbol/dispose
core-js(-pure)/es|stable|actual|full/symbol/has-instance
core-js(-pure)/es|stable|actual|full/symbol/is-concat-spreadable
core-js(-pure)/es|stable|actual|full/symbol/iterator
core-js(-pure)/es|stable|actual|full/symbol/match
core-js(-pure)/es|stable|actual|full/symbol/replace
core-js(-pure)/es|stable|actual|full/symbol/search
core-js(-pure)/es|stable|actual|full/symbol/species
core-js(-pure)/es|stable|actual|full/symbol/split
core-js(-pure)/es|stable|actual|full/symbol/to-primitive
core-js(-pure)/es|stable|actual|full/symbol/to-string-tag
core-js(-pure)/es|stable|actual|full/symbol/unscopables
core-js(-pure)/es|stable|actual|full/symbol/for
core-js(-pure)/es|stable|actual|full/symbol/key-for
core-js(-pure)/es|stable|actual|full/object/get-own-property-symbols
core-js(-pure)/es|stable|actual|full/math/to-string-tag
```
[*Basic example*](https://tinyurl.com/2b2zfvrs):
```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*](https://tinyurl.com/29u2q3jb):
```js
let symbol = Symbol.for('key');
symbol === Symbol.for('key'); // true
Symbol.keyFor(symbol); // 'key'
```
[*Example*](https://tinyurl.com/2297e9bg) 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*](https://tinyurl.com/25s4664f):
```js
Symbol('foo').description; // => 'foo'
// eslint-disable-next-line symbol-description -- example
Symbol().description; // => undefined
```
##### Caveats when using `Symbol` polyfill:[⬆](#index)
- We can't add a new primitive type, `Symbol` returns an object.
- `Symbol.for` and `Symbol.keyFor` can't be polyfilled cross-realm.
- By default, to hide the keys, `Symbol` polyfill defines a setter in `Object.prototype`. For this reason, an uncontrolled creation of symbols can cause a 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](https://tinyurl.com/2blse6aa):
```js
Symbol.useSimple();
let object1 = { [Symbol('symbol1')]: true };
for (let key in object1) console.log(key); // => 'Symbol(symbol1)_t.qamkg9f3q', w/o native Symbol
Symbol.useSetter();
let object2 = { [Symbol('symbol2')]: true };
for (let key in object2) console.log(key); // nothing
```
- Currently, `core-js` does not add 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 are possible with environment exotic objects (for example, IE `localStorage`).
#### ECMAScript: Collections[⬆](#index)
`core-js` uses native collections in most cases, just fixes methods / constructor, if it's required, and in the old environment uses fast polyfill (O(1) lookup).
#### Map[⬆](#index)
Modules [`es.map`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.map.js), [`es.map.group-by`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.map.group-by.js), [`es.map.get-or-insert`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.map.get-or-insert.js) and [`es.map.get-or-insert-computed`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.map.get-or-insert-computed.js).
```ts
class Map {
constructor(iterable?: Iterable<[key, value]>): Map;
clear(): void;
delete(key: any): boolean;
forEach(callbackfn: (value: any, key: any, target: any) => void, thisArg: any): void;
get(key: any): any;
getOrInsert(key: any, value: any): any;
getOrInsertComputed(key: any, (key: any) => value: any): any;
has(key: any): boolean;
set(key: any, val: any): this;
values(): Iterator;
keys(): Iterator;
entries(): Iterator<[key, value]>;
@@iterator(): Iterator<[key, value]>;
readonly attribute size: number;
static groupBy(items: Iterable, callbackfn: (value: any, index: number) => key): Map>;
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/map
core-js(-pure)/es|stable|actual|full/map/group-by
core-js(-pure)/es|stable|actual|full/map/get-or-insert
core-js(-pure)/es|stable|actual|full/map/get-or-insert-computed
```
[*Examples*](https://tinyurl.com/298ekxmq):
```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]]
map = new Map([['a', 1], ['b', 2], ['c', 3]]);
for (let [key, value] of map) {
console.log(key); // => 'a', 'b', 'c'
console.log(value); // => 1, 2, 3
}
for (let value of map.values()) console.log(value); // => 1, 2, 3
for (let key of map.keys()) console.log(key); // => 'a', 'b', 'c'
for (let [key, value] of map.entries()) {
console.log(key); // => 'a', 'b', 'c'
console.log(value); // => 1, 2, 3
}
map = Map.groupBy([1, 2, 3, 4, 5], it => it % 2);
map.get(1); // => [1, 3, 5]
map.get(0); // => [2, 4]
map = new Map([['a', 1]]);
map.getOrInsert('a', 2); // => 1
map.getOrInsert('b', 3); // => 3
map.getOrInsertComputed('a', key => key); // => 1
map.getOrInsertComputed('c', key => key); // => 'c'
console.log(map); // => Map { 'a': 1, 'b': 3, 'c': 'c' }
```
#### Set[⬆](#index)
Modules [`es.set`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.js), [`es.set.difference.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.difference.v2.js), [`es.set.intersection.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.intersection.v2.js), [`es.set.is-disjoint-from.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.is-disjoint-from.v2.js), [`es.set.is-subset-of.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.is-subset-of.v2.js), [`es.set.is-superset-of.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.is-superset-of.v2.js), [`es.set.symmetric-difference.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.symmetric-difference.v2.js), [`es.set.union.v2`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/es.set.union.v2.js)
```ts
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<[value, value]>;
difference(other: SetLike): Set;
intersection(other: SetLike): Set;
isDisjointFrom(other: SetLike): boolean;
isSubsetOf(other: SetLike): boolean;
isSupersetOf(other: SetLike): boolean;
symmetricDifference(other: SetLike): Set;
union(other: SetLike): Set;
@@iterator(): Iterator;
readonly attribute size: number;
}
```
[*CommonJS entry points:*](#commonjs-api)
```
core-js(-pure)/es|stable|actual|full/set
core-js(-pure)/es|stable|actual|full/set/difference
core-js(-pure)/es|stable|actual|full/set/intersection
core-js(-pure)/es|stable|actual|full/set/is-disjoint-from
core-js(-pure)/es|stable|actual|full/set/is-subset-of
core-js(-pure)/es|stable|actual|full/set/is-superset-of
core-js(-pure)/es|stable|actual|full/set/symmetric-difference
core-js(-pure)/es|stable|actual|full/set/union
```
[*Examples*](https://tinyurl.com/2dy5t9ey):
```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']
set = new Set([1, 2, 3, 2, 1]);
for (let value of set) console.log(value); // => 1, 2, 3
for (let value of set.values()) console.log(value); // => 1, 2, 3
for (let key of set.keys()) console.log(key); // => 1, 2, 3
for (let [key, value] of set.entries()) {
console.log(key); // => 1, 2, 3
console.log(value); // => 1, 2, 3
}
new Set([1, 2, 3]).union(new Set([3, 4, 5])); // => Set {1, 2, 3, 4, 5}
new Set([1, 2, 3]).intersection(new Set([3, 4, 5])); // => Set {3}
new Set([1, 2, 3]).difference(new Set([3, 4, 5])); // => Set {1, 2}
new Set([1, 2, 3]).symmetricDiffere