Babel

Babel is a JavaScript compiler that converts modern ECMAScript 2015+ code into backwards compatible versions for legacy environments.

Babel is the workhorse of the modern web: it compiles the latest JavaScript syntax (like optional chaining and private class features) into code that older browsers can actually execute. The tool operates through a system of plugins and presets (such as @babel/preset-env) that allow developers to target specific environments with precision. It handles JSX for React and strips types from TypeScript, making it foundational for most front-end builds. Major players like Netflix and Airbnb rely on Babel to keep their codebases modern while maintaining broad compatibility across the global user base.

https://babeljs.io/