Babel

Babel is the transpiler that made ES6+ possible. While slower than SWC/esbuild, it remains the most extensible compiler with the largest plugin ecosystem.

When to Use

• Custom Transformations: You need to write a custom AST transform for your framework.
• Legacy Browser Support: preset-env with core-js is still the gold standard for "make it run on IE11" (if you must).

Core Concepts

Presets

@babel/preset-env, @babel/preset-react, @babel/preset-typescript.

Plugins

Small transforms. plugin-transform-runtime.