Babel

Babel is a free open-source JavaScript compiler created by Sebastian McKenzie in 2014, originally called six to five for transpiling ES6 to ES5, now maintained by an independent team and downloaded over fifty million times weekly from npm, enabling developers to use the latest JavaScript and TypeScript language features while maintaining compatibility with older browsers and runtime environments by transforming modern syntax into equivalent code that runs on any platform. The transpilation pipeline parses source code into an abstract syntax tree using the Babylon parser, applies a configurable series of plugin transformations to the tree, and generates output code targeting specific browser or Node.js versions, with presets bundling commonly used plugins for convenience including the env preset that automatically determines necessary transformations based on browser target configuration. The plugin architecture enables extending the compiler with custom syntax transformations, with the official distribution providing dozens of plugins for language proposals, JSX transformation for React, TypeScript stripping, and experimental features not yet standardized. The polyfill integration through core-js provides runtime implementations of new APIs that cannot be achieved through syntax transformation alone, ensuring that methods like Array dot includes and Object dot fromEntries work on older platforms. The source map generation enables debugging original source code in browser devtools. The caching accelerates rebuilds. The monorepo support handles complex projects. Designed for JavaScript developers, library authors, and build engineers.