Polyfill
ELI5 — The Vibe Check
A polyfill is a piece of code that teaches old browsers new tricks. Browser doesn't support Promise? Here's a polyfill that fakes it. It's like giving your grandpa a smartphone tutorial so he can use the same apps as everyone else. Filling the poly... gaps.
Real Talk
A polyfill is JavaScript code that implements a modern web API or feature in browsers that don't natively support it. Polyfills enable developers to use newer language features and browser APIs while maintaining backward compatibility with older environments.
When You'll Hear This
"We polyfilled fetch for IE11 users, all three of them" / "core-js provides polyfills for almost every ES feature"
Related Terms
Autoprefixer
Autoprefixer is the robot that adds -webkit-, -moz-, and all those annoying vendor prefixes to your CSS so you don't have to.
Babel
Babel is the universal translator for JavaScript.
Progressive Enhancement
Progressive Enhancement is the philosophy of building the basics first (HTML that works), then layering on CSS and JavaScript like frosting on a cake.