core-js-compat

What is core-js-compat?

The core-js-compat package provides compatibility data for core-js, which is a modular standard library for JavaScript, including polyfills for ECMAScript up to the latest standards. It is useful for developers who need to know which features are available in core-js for a specific version of a browser or Node.js.

What are core-js-compat's main functionalities?

Compatibility Data Retrieval

Retrieve a list of features supported by core-js for a specific environment, such as Chrome 70.

const { list } = require('core-js-compat')({ targets: 'chrome 70' });

Custom Build Generation

Generate a list of core-js modules required to support a specific target, such as Internet Explorer 11, with a specific version of core-js.

const { getModulesListForTargetVersion } = require('core-js-compat');
const modulesList = getModulesListForTargetVersion({ targets: { ie: 11 }, version: '3.6' });

Other packages similar to core-js-compat

babel-polyfill

Babel-polyfill is a package that includes Babel transforms and a polyfill that includes a custom regenerator runtime and core-js. It is similar to core-js-compat in that it provides polyfills for ECMAScript features, but it is less modular and is deprecated in favor of directly including core-js and regenerator-runtime.

es6-shim

The es6-shim package provides polyfills for ECMAScript 6 (also known as ECMAScript 2015) features. It is similar to core-js-compat in providing polyfills, but it is focused only on ES6 features and does not provide the modular approach or the compatibility data that core-js-compat offers.

polyfill-service

The polyfill-service package by Financial Times provides a service that returns a set of polyfills based on the user-agent string of the browser making the request. It is similar to core-js-compat in that it aims to provide polyfills for compatibility, but it does so as a service rather than a package to include in your project.

README

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

core-js-compat package contains data about the necessity of core-js modules and API for getting a list of required core-js modules by browserslist query.

import compat from 'core-js-compat';

const {
  list,                       // array of required modules
  targets,                    // object with targets for each module
} = compat({
  targets: '> 1%',            // browserslist query or object of minimum environment versions to support, see below
  modules: [                  // optional list / filter of modules - regex, string or an array of them:
    'core-js/actual',         // - an entry point
    'esnext.array.unique-by', // - a module name (or just a start of a module name)
    /^web\./,                 // - regex that a module name must satisfy
  ],
  exclude: [                  // optional list / filter of modules to exclude, the signature is similar to `modules` option
    'web.atob',
  ],
  version: '3.42',            // used `core-js` version, by default - the latest
  inverse: false,             // inverse of the result - shows modules that are NOT required for the target environment
});

console.log(targets);
/* =>
{
  'es.error.cause': { ios: '14.5-14.8' },
  'es.aggregate-error.cause': { ios: '14.5-14.8' },
  'es.array.at': { ios: '14.5-14.8' },
  'es.array.find-last': { firefox: '100', ios: '14.5-14.8' },
  'es.array.find-last-index': { firefox: '100', ios: '14.5-14.8' },
  'es.array.includes': { firefox: '100' },
  'es.array.push': { chrome: '100', edge: '101', ios: '14.5-14.8', safari: '15.4' },
  'es.array.unshift': { ios: '14.5-14.8', safari: '15.4' },
  'es.object.has-own': { ios: '14.5-14.8' },
  'es.regexp.flags': { chrome: '100', edge: '101' },
  'es.string.at-alternative': { ios: '14.5-14.8' },
  'es.typed-array.at': { ios: '14.5-14.8' },
  'es.typed-array.find-last': { firefox: '100', ios: '14.5-14.8' },
  'es.typed-array.find-last-index': { firefox: '100', ios: '14.5-14.8' },
  'esnext.array.group': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.group-by': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.group-by-to-map': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.group-to-map': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.to-reversed': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.to-sorted': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.to-spliced': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.unique-by': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.array.with': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.typed-array.to-reversed': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.typed-array.to-sorted': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.typed-array.to-spliced': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'esnext.typed-array.with': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'web.dom-exception.stack': { chrome: '100', edge: '101', ios: '14.5-14.8', safari: '15.4' },
  'web.immediate': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' },
  'web.structured-clone': { chrome: '100', edge: '101', firefox: '100', ios: '14.5-14.8', safari: '15.4' }
}
*/

targets option

targets could be a browserslist query or a targets object that specifies minimum environment versions to support:

// browserslist query:
'defaults, not IE 11, maintained node versions';
// object (sure, all those fields optional):
({
  android: '4.0',         // Android WebView version
  bun: '0.1.2',           // Bun version
  chrome: '38',           // Chrome version
  'chrome-android': '18', // Chrome for Android version
  deno: '1.12',           // Deno version
  edge: '13',             // Edge version
  electron: '5.0',        // Electron framework version
  firefox: '15',          // Firefox version
  'firefox-android': '4', // Firefox for Android version
  hermes: '0.11',         // Hermes version
  ie: '8',                // Internet Explorer version
  ios: '13.0',            // iOS Safari version
  node: 'current',        // NodeJS version, you can use 'current' for set it to currently used
  opera: '12',            // Opera version
  'opera-android': '7',   // Opera for Android version
  phantom: '1.9',         // PhantomJS headless browser version
  quest: '5.0',           // Meta Quest Browser version
  'react-native': '0.70', // React Native version (default Hermes engine)
  rhino: '1.7.13',        // Rhino engine version
  safari: '14.0',         // Safari version
  samsung: '14.0',        // Samsung Internet version
  /**
   * true option set target to minimum supporting ES Modules versions of all browsers, ignoring `browsers` target.
   * 'intersect' option intersects the `browsers` target and `browserslist`'s targets. The maximum version will be used.
   */
  esmodules: true | 'intersect',
  browsers: '> 0.25%',    // Browserslist query or object with target browsers
});

Additional API:

// equals of of the method from the example above
require('core-js-compat/compat')({ targets, modules, version }); // => { list: Array<ModuleName>, targets: { [ModuleName]: { [EngineName]: EngineVersion } } }
// or
require('core-js-compat').compat({ targets, modules, version }); // => { list: Array<ModuleName>, targets: { [ModuleName]: { [EngineName]: EngineVersion } } }

// full compat data:
require('core-js-compat/data'); // => { [ModuleName]: { [EngineName]: EngineVersion } }
// or
require('core-js-compat').data; // => { [ModuleName]: { [EngineName]: EngineVersion } }

// map of modules by `core-js` entry points:
require('core-js-compat/entries'); // => { [EntryPoint]: Array<ModuleName> }
// or
require('core-js-compat').entries; // => { [EntryPoint]: Array<ModuleName> }

// full list of modules:
require('core-js-compat/modules'); // => Array<ModuleName>
// or
require('core-js-compat').modules; // => Array<ModuleName>

// the subset of modules which available in the passed `core-js` version:
require('core-js-compat/get-modules-list-for-target-version')('3.42'); // => Array<ModuleName>
// or
require('core-js-compat').getModulesListForTargetVersion('3.42'); // => Array<ModuleName>

If you wanna help to improve this data, you could take a look at the related section of CONTRIBUTING.md. The visualization of compatibility data and the browser tests runner is available here, the example:

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