The Core.js GitHub Library is being used on 25,000+ websites.

core-js (as the authors/developers write it) is a JavaScript library that aims to help developers with core utility functions and methods. It's general goal is to fill in some perceived missing features of JavaScript, including some explicit polyfills.

It will provide help for Array, Object, Number and a range of other native JavaScript object types. Part of the perceived goal is to lower dependency on JavaScript frameworks (like jQuery), which often offer similar helper methods/functions/utilities, but bundle them up into less flexible object types.

This framework is actively being developed in 2019, and features a range of contributors.