core-js-bundle

I highly recommend reading this: So, what's next?

Modular standard library for JavaScript. Includes polyfills for ECMAScript up to 2023: 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.

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, Boosty, Bitcoin ( bc1qlea7544qtsmj2rayg0lthvza9fau63ux0fstcz ), Alipay.

Example of usage:

import 'core-js/actual';

Promise.resolve(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]

(function * (i) { while (true) yield i++; })(1)
  .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:

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.resolve(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]

(function * (i) { while (true) yield i++; })(1)
  .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:

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.resolve(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.from(function * (i) { while (true) yield i++; }(1))
  .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])

It's a bundled global version, for more info see core-js documentation.

Changelog

3.42.0 - 2025.04.30

• Changes v3.41.0...v3.42.0 (142 commits)
• Map upsert proposal:
  • Moved to stage 2.7, April 2025 TC39 meeting
  • Validation order of WeakMap.prototype.getOrInsertComputed updated following tc39/proposal-upsert#79
  • Built-ins:
    • Map.prototype.getOrInsert
    • Map.prototype.getOrInsertComputed
    • WeakMap.prototype.getOrInsert
    • WeakMap.prototype.getOrInsertComputed
• Don't call well-known Symbol methods for RegExp on primitive values following tc39/ecma262#3009:
  • For avoid performance regression, temporarily, only in own core-js implementations
  • Built-ins:
    • String.prototype.matchAll
    • String.prototype.match
    • String.prototype.replaceAll
    • String.prototype.replace
    • String.prototype.search
    • String.prototype.split
• Added workaround for the Uint8Array.prototype.setFromBase64 bug in some of Linux builds of WebKit
• Implemented early-error iterator closing following tc39/ecma262#3467, including fix of a WebKit bug, in the following methods:
  • Iterator.prototype.drop
  • Iterator.prototype.every
  • Iterator.prototype.filter
  • Iterator.prototype.find
  • Iterator.prototype.flatMap
  • Iterator.prototype.forEach
  • Iterator.prototype.map
  • Iterator.prototype.reduce
  • Iterator.prototype.some
  • Iterator.prototype.take
• Fixed missing forced replacement of AsyncIterator helpers
• Added closing of sync iterator when async wrapper yields a rejection following tc39/ecma262#2600. Affected methods:
  • Array.fromAsync (due to the lack of async feature detection capability - temporarily, only in own core-js implementation)
  • AsyncIterator.from
  • Iterator.prototype.toAsync
• Added detection for throwing on undefined initial parameter in Iterator.prototype.reduce (see WebKit bug)
• core-js-compat and core-js-builder API:
  • Added 'intersect' support for targets.esmodules (Babel 7 behavior)
  • Fixed handling of targets.esmodules: true (Babel 7 behavior)
• Compat data improvements:
  • Explicit Resource Management features disabled (again) in V8 ~ Chromium 135 and re-added in 136
  • RegExp.escape marked as shipped from V8 ~ Chromium 136
  • Error.isError marked as shipped from FF138
  • Explicit Resource Management features re-enabled in Deno 2.2.10
  • Iterator helpers proposal features marked as supported from Deno 1.38.1 since it seems they were disabled in 1.38.0
  • Iterator.prototype.{ drop, reduce, take } methods marked as fixed in Bun 1.2.11
  • Added NodeJS 24.0 compat data mapping
  • Updated Electron 36 and added Electron 37 compat data mapping
  • Added Opera Android 88 and 89 compat data mapping
  • Added Oculus Quest Browser 37 compat data mapping