A polyfill is a piece of code used to provide modern functionality on older browsers that do not natively support it. That is Cross-browser compatibility for
Polyfill - Cross-Browser Support for JavaScript Projects (Support upto IE 8+) using React & Core JS
Polyfills: everything you ever wanted to know, or maybe a bit less, by David Gilbertson
React: Implement differential loading to load polyfills only in the legacy/old browser, by Sumeet Roy
Polyfill - Cross-Browser Support for JavaScript Projects (Support upto IE 8+) using React & Core JS
How Polyfills Remove Browser Compatibility, by Samuel Gómez, Valtech Switzerland
How to add Polyfills to your Javascript code
core-js/docs/2023-02-14-so-whats-next.md at master · zloirock/core-js · GitHub
core-js/docs/2023-02-14-so-whats-next.md at master · zloirock/core-js · GitHub
Polyfills: everything you ever wanted to know, or maybe a bit less, by David Gilbertson