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core-js

Standard library


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Maintainers
1
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32,783,211
decreased by-7.21%

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Package description

What is core-js?

The core-js npm package is a modular standard library for JavaScript, which includes polyfills for ECMAScript features. It provides reliable polyfills to ensure that code behaves consistently across different environments, including older browsers.

What are core-js's main functionalities?

Polyfilling ECMAScript features

This feature allows developers to use the latest ECMAScript features while ensuring backward compatibility with older environments that do not support these features natively.

require('core-js/stable');
// Now you can use ES6 features like Promise in environments that do not support them natively.

Polyfilling Web Standards

Core-js can also polyfill web standards, allowing developers to use modern web APIs in environments that have not implemented them.

require('core-js/web');
// This includes polyfills for web standards like DOM collections (e.g., NodeList), timers, and more.

Polyfilling Proposals

Developers can experiment with proposed ECMAScript features before they are finalized and adopted into the standard, ensuring forward compatibility.

require('core-js/proposals');
// This will include polyfills for ECMAScript proposals that are not yet part of the standard.

Other packages similar to core-js

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Open Collective version core-js downloads core-js-pure downloads tests eslint

Modular standard library for JavaScript. Includes polyfills for ECMAScript up to 2021: promises, symbols, collections, iterators, typed arrays, many other features, ECMAScript proposals, some cross-platform WHATWG / W3C features and proposals like URL. You can load only required features or use it without global namespace pollution.

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

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

Raising funds

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




Example of usage:

import 'core-js/actual'; // <- at the top of your entry point

Array.from(new Set([1, 2, 3, 2, 1]));          // => [1, 2, 3]
[1, 2, 3, 4, 5].group(it => it % 2);           // => { 1: [1, 3, 5], 0: [2, 4] }
Promise.resolve(42).then(x => console.log(x)); // => 42
structuredClone(new Set([1, 2, 3]));           // => new Set([1, 2, 3])
queueMicrotask(() => console.log('called as microtask'));

You can load only required features:

import 'core-js/actual/array/from';       // <- at the top of your entry point
import 'core-js/actual/array/group';      // <- at the top of your entry point
import 'core-js/actual/set';              // <- at the top of your entry point
import 'core-js/actual/promise';          // <- at the top of your entry point
import 'core-js/actual/structured-clone'; // <- at the top of your entry point
import 'core-js/actual/queue-microtask';  // <- at the top of your entry point

Array.from(new Set([1, 2, 3, 2, 1]));          // => [1, 2, 3]
[1, 2, 3, 4, 5].group(it => it % 2);           // => { 1: [1, 3, 5], 0: [2, 4] }
Promise.resolve(42).then(x => console.log(x)); // => 42
structuredClone(new Set([1, 2, 3]));           // => new Set([1, 2, 3])
queueMicrotask(() => console.log('called as microtask'));

Or use it without global namespace pollution:

import from from 'core-js-pure/actual/array/from';
import group from 'core-js-pure/actual/array/group';
import Set from 'core-js-pure/actual/set';
import Promise from 'core-js-pure/actual/promise';
import structuredClone from 'core-js-pure/actual/structured-clone';
import queueMicrotask from 'core-js-pure/actual/queue-microtask';

from(new Set([1, 2, 3, 2, 1]));                // => [1, 2, 3]
group([1, 2, 3, 4, 5], it => it % 2);          // => { 1: [1, 3, 5], 0: [2, 4] }
Promise.resolve(42).then(x => console.log(x)); // => 42
structuredClone(new Set([1, 2, 3]));           // => new Set([1, 2, 3])
queueMicrotask(() => console.log('called as microtask'));

It's a global version (first 2 examples), for more info see core-js documentation.

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Last updated on 09 Jul 2022

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