What about source maps?

Enable the toggle and the tool emits `app.min.js` with a `//# sourceMappingURL` comment plus the matching `.map` file, both downloadable.

Will it mangle global variables?

Not by default. Enable Top-level to mangle and drop unused top-level declarations in a module or script you fully control, and list names to protect under Reserved names.

Can it minify TypeScript or JSX?

Terser only parses plain JavaScript. Use Beautify for TS/JSX formatting, or transpile with tsc/esbuild first and minify the output.

JavaScript Minifier

Compress JavaScript in your browser with Terser: mangle, compress, drop console and debugger, pick an ECMAScript target, keep function and class names, reserve identifiers and emit source maps. Or switch to Beautify to format JavaScript, JSX, TypeScript and TSX with Prettier. Every run reports the real gzip size (CompressionStream), not an estimate.

Runs locally in your browser

For long source files, open fullscreen for a wider view

Target

File

Source

649 chars · 32 lines

Minified

Output will appear here…

Input

649 B

Minified

0 B

Saved

—

Compression

—

Gzip (output)

—

Gzip (input)

—

Compress (dead code, inlining, constant folding)Mangle local variable namesModule (ES modules, implies strict mode)Top-level: mangle/drop unused top-level declarationsKeep function names (fn.name / stack traces)Keep class namesDrop console.*Drop debugger statementsGenerate source map (app.min.js.map)

Reserved names (never mangled)

Comments

The ECMAScript target lets terser use newer syntax for smaller output (e.g. arrow functions, optional chaining at ES2020+). Pick ES5 only if you must support very old browsers — it does not transpile, it just avoids emitting newer constructs.

CSS Minifier

Minify CSS safely — strings, url() and calc() preserved — with gzip size and duplicate-selector merging.

JSON Minifier

Minify JSON, strip nulls, measure gzip size and encode as Base64 or URL-safe text.

HTML / CSS Prettifier

Beautify or minify HTML, CSS, SCSS, Less, JS, TS, JSON, YAML, Markdown and more — with preview and lint.

How to use JavaScript Minifier

1Paste JavaScript and choose Minify (terser) or Beautify (prettier); for TS/JSX use Beautify.
2Pick the ECMAScript target and toggle compress, mangle, module, top-level, keep names and console/debugger dropping.
3List reserved names that must not be mangled and decide which comments to keep.
4Enable the source map to download app.min.js and app.min.js.map with matching names.
5Compare input, output and real gzip sizes in the stats.

About JavaScript Minifier

JavaScript Minifier is part of FizzKit — a collection of focused developer and ad-tech tools. Because everything runs locally, it works offline once loaded and never exposes your data to a remote server.

Frequently asked questions

No. Terser and Prettier run entirely in your browser; nothing is uploaded.

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