JavaScript Minifier

Minified or gzipped — which number matters?

Every JavaScript minifier reports raw bytes saved, and no browser has ever downloaded raw bytes — real transport runs through gzip or brotli first. Unlike CSS, JavaScript minification genuinely earns its keep after gzip too, because renaming variables removes redundancy gzip cannot reach on its own. Measured: jQuery 3.7.1 goes from 285,314 to 87,533 bytes raw with Terser's compress and mangle (69.3% smaller), and after gzip the gap is still 83,890 versus 30,406 bytes — a 63.8% saving. bootstrap.bundle.js shows the same pattern: 61.2% smaller raw, 46.2% smaller gzipped. Compare that to CSS, where minifying Bootstrap's stylesheet saves 17.2% raw but only 7.4% once gzip runs — gzip was already eating most of that redundancy. The Size tab on this page measures both numbers for your actual file, with CompressionStream, never estimated.

What this minifier will not do to your file

This page's own written code is a tokenizer and a token-level beautifier (src/lib/tools/minify/js/tokenize.ts and format.ts) — the actual minifying is done by a vendored copy of Terser 5.51.2, loaded from this site's own server and hash-pinned so it cannot silently change. That distinction matters because the hard correctness questions in JavaScript minification — Automatic Semicolon Insertion making a bare return followed by a newline mean something different from return followed by an expression, or a private class field like #count needing to be renamed consistently everywhere it is referenced without colliding with another private name — require real scope analysis. Measured against this page's own fixture: Terser reads a return statement's trailing newline as ending the function, exactly per the specification, and renames #count to a new private name everywhere it is used, never treating the # as separable from the name that follows it. A hand-written, regex-based minifier that got either of these wrong would ship broken code with no warning.

Licence comments are the other correctness question this page takes seriously: a /*! ... */ or /** @license ... */ marker is a legal object under MIT, BSD and Apache licences, and this tool keeps them by default — mapped onto Terser's own comments: "some" mode — rather than stripping every comment as a blanket default.

Minification is not obfuscation

Minified JavaScript is trivially beautified back — this page's own Beautify mode does exactly that, restoring indentation and line structure from the token stream — so mangling variable names provides no real secrecy for proprietary logic. It is also not compression: gzip and brotli do the actual byte-shrinking work at transport time, and Terser's job is to remove redundancy (long names, dead code, whitespace) before compression even starts. What minification genuinely buys you, especially for JavaScript, is removing redundancy that compression cannot reach on its own — see the gzip section above for the measured difference that makes.

Common use cases

• Shrinking a script or a small bundle before shipping it, with licence notices intact
• Combining several JavaScript files into one, minified together, in a stated order
• Checking whether a mangled build still parses cleanly before it ships
• Reading a minified third-party script by beautifying it first
• Seeing which Terser setting — compress, mangle, or comment handling — earned which bytes