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# core-js [](#raising-funds) [](#raising-funds) [](https://gitter.im/zloirock/core-js?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) [](https://www.npmjs.com/package/core-js) [](http://npm-stat.com/charts.html?package=core-js&author=&from=2014-11-18) [](https://travis-ci.org/zloirock/core-js) [](https://david-dm.org/zloirock/core-js?type=dev) ## As advertising: the author is looking for a good job :) ## [core-js@3, babel and a look into the future](https://github.com/zloirock/core-js/tree/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md) ## Raising funds `core-js` isn't backed by a company, so the future of this project depends on you. Become a sponsor or a backer [**on Open Collective**](https://opencollective.com/core-js) or [**on Patreon**](https://www.patreon.com/zloirock) if you are interested in `core-js`. --- <a href="https://opencollective.com/core-js/sponsor/0/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/0/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/1/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/1/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/2/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/2/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/3/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/3/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/4/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/4/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/5/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/5/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/6/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/6/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/7/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/7/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/8/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/8/avatar.svg"></a><a href="https://opencollective.com/core-js/sponsor/9/website" target="_blank"><img src="https://opencollective.com/core-js/sponsor/9/avatar.svg"></a> --- <a href="https://opencollective.com/core-js#backers" target="_blank"><img src="https://opencollective.com/core-js/backers.svg?width=890"></a> --- **It's documentation for obsolete `core-js@2`. If you looking documentation for actual `core-js` version, please, check [this branch](https://github.com/zloirock/core-js/tree/master).** Modular standard library for JavaScript. Includes polyfills for [ECMAScript 5](#ecmascript-5), [ECMAScript 6](#ecmascript-6): [promises](#ecmascript-6-promise), [symbols](#ecmascript-6-symbol), [collections](#ecmascript-6-collections), iterators, [typed arrays](#ecmascript-6-typed-arrays), [ECMAScript 7+ proposals](#ecmascript-7-proposals), [setImmediate](#setimmediate), etc. Some additional features such as [dictionaries](#dict) or [extended partial application](#partial-application). You can require only needed features or use it without global namespace pollution. [*Example*](http://goo.gl/a2xexl): ```js Array.from(new Set([1, 2, 3, 2, 1])); // => [1, 2, 3] '*'.repeat(10); // => '**********' Promise.resolve(32).then(x => console.log(x)); // => 32 setImmediate(x => console.log(x), 42); // => 42 ``` [*Without global namespace pollution*](http://goo.gl/paOHb0): ```js var core = require('core-js/library'); // With a modular system, otherwise use global `core` core.Array.from(new core.Set([1, 2, 3, 2, 1])); // => [1, 2, 3] core.String.repeat('*', 10); // => '**********' core.Promise.resolve(32).then(x => console.log(x)); // => 32 core.setImmediate(x => console.log(x), 42); // => 42 ``` ### Index - [Usage](#usage) - [Basic](#basic) - [CommonJS](#commonjs) - [Custom build](#custom-build-from-the-command-line) - [Supported engines](#supported-engines) - [Features](#features) - [ECMAScript 5](#ecmascript-5) - [ECMAScript 6](#ecmascript-6) - [ECMAScript 6: Object](#ecmascript-6-object) - [ECMAScript 6: Function](#ecmascript-6-function) - [ECMAScript 6: Array](#ecmascript-6-array) - [ECMAScript 6: String](#ecmascript-6-string) - [ECMAScript 6: RegExp](#ecmascript-6-regexp) - [ECMAScript 6: Number](#ecmascript-6-number) - [ECMAScript 6: Math](#ecmascript-6-math) - [ECMAScript 6: Date](#ecmascript-6-date) - [ECMAScript 6: Promise](#ecmascript-6-promise) - [ECMAScript 6: Symbol](#ecmascript-6-symbol) - [ECMAScript 6: Collections](#ecmascript-6-collections) - [ECMAScript 6: Typed Arrays](#ecmascript-6-typed-arrays) - [ECMAScript 6: Reflect](#ecmascript-6-reflect) - [ECMAScript 7+ proposals](#ecmascript-7-proposals) - [stage 4 proposals](#stage-4-proposals) - [stage 3 proposals](#stage-3-proposals) - [stage 2 proposals](#stage-2-proposals) - [stage 1 proposals](#stage-1-proposals) - [stage 0 proposals](#stage-0-proposals) - [pre-stage 0 proposals](#pre-stage-0-proposals) - [Web standards](#web-standards) - [setTimeout / setInterval](#settimeout--setinterval) - [setImmediate](#setimmediate) - [iterable DOM collections](#iterable-dom-collections) - [Non-standard](#non-standard) - [Object](#object) - [Dict](#dict) - [partial application](#partial-application) - [Number Iterator](#number-iterator) - [escaping strings](#escaping-strings) - [delay](#delay) - [helpers for iterators](#helpers-for-iterators) - [Missing polyfills](#missing-polyfills) - [Changelog](./CHANGELOG.md) ## Usage ### Basic ``` npm i core-js bower install core.js ``` ```js // Default require('core-js'); // Without global namespace pollution var core = require('core-js/library'); // Shim only require('core-js/shim'); ``` If you need complete build for browser, use builds from `core-js/client` path: * [default](https://raw.githack.com/zloirock/core-js/v2.6.12/client/core.min.js): Includes all features, standard and non-standard. * [as a library](https://raw.githack.com/zloirock/core-js/v2.6.12/client/library.min.js): Like "default", but does not pollute the global namespace (see [2nd example at the top](#core-js)). * [shim only](https://raw.githack.com/zloirock/core-js/v2.6.12/client/shim.min.js): Only includes the standard methods. Warning: if you use `core-js` with the extension of native objects, require all needed `core-js` modules at the beginning of entry point of your application, otherwise, conflicts may occur. ### CommonJS You can require only needed modules. ```js require('core-js/fn/set'); require('core-js/fn/array/from'); require('core-js/fn/array/find-index'); Array.from(new Set([1, 2, 3, 2, 1])); // => [1, 2, 3] [1, 2, NaN, 3, 4].findIndex(isNaN); // => 2 // or, w/o global namespace pollution: var Set = require('core-js/library/fn/set'); var from = require('core-js/library/fn/array/from'); var findIndex = require('core-js/library/fn/array/find-index'); from(new Set([1, 2, 3, 2, 1])); // => [1, 2, 3] findIndex([1, 2, NaN, 3, 4], isNaN); // => 2 ``` Available entry points for methods / constructors, as above examples, and namespaces: for example, `core-js/es6/array` (`core-js/library/es6/array`) contains all [ES6 `Arra