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 version without global namespace pollution (the third example), for more info see core-js documentation.