Core-js is a modular standard library for JavaScript. It provides polyfills for ECMAScript, including promises, symbols, collections, iterators, typed arrays and various other features. Core-js also supports ECMAScript proposals and some cross-platform WHATWG / W3C features and proposals, like URL. You can choose to load only the features you need or use it without the pollution of the global namespace.
To use Core-js, you can simply import it into your JavaScript file. Here is an example of using the whole library:
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]
If you only need certain features, you can import them individually:
import 'core-js/actual/promise';
import 'core-js/actual/iterator';
Promise.resolve(42).then(it => console.log(it)); // => 42
To avoid global namespace pollution, use the 'core-js-pure' import pattern:
import Promise from 'core-js-pure/actual/promise';
Promise.resolve(42).then(it => console.log(it)); // => 42
The core-js documentation is available in its GitHub repository. This comprehensive guide provides deeper insights into the package's functionality, usage examples, and additional resources for better understanding and implementation.
