JavaScript Minifier

Usually 50–70 % of the original size: comments and whitespace go, local variable and function names become single letters, and Terser’s compressor folds constants, removes dead code and shortens expressions (true → !0, undefined → void 0). Gzip on top of that brings a typical 100 KB script to about 15 KB over the wire.

Yes, with the standard caveats of every minifier. Terser only renames identifiers that are local to a scope, so exported names, global variables, object keys and string property access stay intact. Code that relies on Function.prototype.toString or on a variable’s name at runtime is the rare exception; untick “Shorten variable names” for such files.

Terser, the maintained successor of UglifyJS that supports modern syntax (ES2015+ through ES2024 modules, async, classes, optional chaining). esbuild and SWC minify faster in build pipelines but need a native binary; Terser runs as plain JavaScript in the browser, which is what makes an upload-free tool possible.

Only for one-off scripts: a WordPress snippet, a Google Tag Manager custom HTML tag, an inline script in a static site or a browser extension. Anything with a build step (Vite, Next.js, webpack, Rollup) already minifies on build; keep the readable source and never edit the minified copy.

No source map is produced here. To read minified code again use the JavaScript formatter — it restores layout, though not the original variable names.