bundler

A bundler is a tool that stitches your many source files — JavaScript, CSS, images, and the libraries they pull in — into a few small, optimized files a browser can download and run fast. You write code split across dozens of tidy files; the bundler packs them for the trip.

It also tidies along the way: removing dead code, shrinking file sizes, and translating newer syntax so older browsers cope. The result is far fewer downloads, so your page loads quicker.

Vite, webpack, and esbuild are the popular ones today. You mostly meet a bundler through a 'build' step that turns your readable project into the lean bundle you actually ship.