Babel

Babel is a transpiler: a tool that turns source code into other source code at the same level. It reads your JavaScript, parses it into a syntax tree, lets plugins transform that tree and prints new code. It started in 2014 as 6to5, a tool that let developers write the then-new ES6 syntax and still run it in older browsers, and was renamed Babel in 2015.

Each transformation is a plugin, and presets bundle many of them. @babel/preset-env compiles only the syntax your target browsers lack, based on a Browserslist query such as > 0.5%, not dead; @babel/preset-react turns JSX into function calls; and @babel/preset-typescript strips type annotations. Plugins can also do custom work, such as removing debug code or adding test coverage counters, and the React Compiler, which adds memoization automatically, ships as a Babel plugin.

Babel 8, released in June 2026 after eight years of Babel 7, is published only as ES modules, needs Node.js 22 or later, and by default targets Browserslist's defaults query instead of compiling everything down to ES5. Over the same years, much of Babel's everyday work moved to faster tools written in Go and Rust, such as esbuild, SWC and Oxc, which Next.js and Vite use by default; Babel remains common where its plugins are needed.

Babel is often confused with a bundler and with a polyfill. A bundler such as webpack combines many files into a few and can run Babel on each one through babel-loader; Babel itself transforms one file at a time. Babel rewrites syntax, such as optional chaining or classes, but can't add missing built-in functions such as Array.prototype.at; those come from polyfills, for example core-js, which a separate Babel plugin can insert where needed. It also strips TypeScript types without checking them, so projects still run tsc to catch type errors.