# core-js
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## 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`.
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---
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---
**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}