core-js is a modular standard library for JavaScript that provides polyfills and ponyfills for ECMAScript features and web standards.
The tool solves the problem of using modern JavaScript features in environments that do not yet support them. It includes polyfills for ECMAScript up to 2025, covering promises, symbols, collections, iterators, typed arrays, and many other features, as well as ECMAScript proposals and cross-platform WHATWG and W3C features like URL and URLSearchParams. The modular approach allows developers to load only the features they need or use the library without polluting the global namespace.
Developers should choose core-js when they need to support older JavaScript environments while writing code using modern language features. It suits projects that must maintain broad compatibility across different runtime versions. The tool is particularly valuable for library authors and applications targeting diverse user bases where transpilation alone is insufficient.
The project is maintained independently without backing from a company, relying on community sponsorship for sustainability. Development activity shows ongoing engagement with the JavaScript standards process, as the tool tracks and implements features from ECMAScript proposals and web standards specifications. The maintainer actively communicates about the project's direction and future through blog posts and documentation updates on the project's dedicated website.
