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.
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.Babel-polyfill is a package that provides polyfills necessary for a full ES2015+ environment. It is similar to core-js but is more tightly coupled with Babel's transpilation process.
The es6-shim package provides polyfills for ECMAScript 6 (aka ECMAScript 2015) features. It is similar to core-js but focuses specifically on ES6 features and does not cover proposals or web standards.
The polyfill-service by Financial Times is an online service that provides polyfills based on the user's browser. It is different from core-js in that it is a service rather than a package you include in your project, but it serves a similar purpose in polyfilling features.
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.
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.
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 global version (first 2 examples), for more info see core-js documentation.
Iterator helpers proposal:
Iterator
Iterator.fromIterator.prototype.dropIterator.prototype.everyIterator.prototype.filterIterator.prototype.findIterator.prototype.flatMapIterator.prototype.forEachIterator.prototype.mapIterator.prototype.reduceIterator.prototype.someIterator.prototype.takeIterator.prototype.toArrayIterator.prototype[@@toStringTag]es. namespace modules, /es/ and /stable/ namespaces entriesPromise.try:
Promise.tryes. namespace module, /es/ and /stable/ namespaces entries/actual|full/promise/try entries for the callback arguments supportMath.sumPrecise proposal:
Math.sumPrecise/actual/ namespace entries, unconditional forced replacement changed to feature detectionIterator sequencing stage 2.7 proposal:
Iterator.concatMap upsert stage 2 proposal:
Map.prototype.getOrInsertMap.prototype.getOrInsertComputedWeakMap.prototype.getOrInsertWeakMap.prototype.getOrInsertComputed@@species pattern removed from %TypedArray% and ArrayBuffer methods, tc39/ecma262/3450:
%TypedArray%.prototype.filter%TypedArray%.prototype.filterReject%TypedArray%.prototype.map%TypedArray%.prototype.slice%TypedArray%.prototype.subarrayArrayBuffer.prototype.sliceUint8Array to / from base64 and hex proposal methods marked as shipped from FF133self descriptor is fixed in Deno 1.46.0Iterator helpers proposal methods marked as shipped from Bun 1.1.31FAQs
Standard library
The npm package core-js receives a total of 34,656,045 weekly downloads. As such, core-js popularity was classified as popular.
We found that core-js demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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