Minify JavaScript

No, and for source code that is the point. Nothing is uploaded and no request leaves your device. Pasting proprietary source into an online minifier that posts it to a server is a disclosure, whatever the site says about retention — and it is exactly the sort of thing that is done in a hurry without thinking.

Almost certainly, yes. This is terser, which is what webpack, Rollup, Vite and most other bundlers use to minify. The difference is only that it runs here, in your browser, rather than on your machine or a server.

It should not, and that is checked rather than assumed: our tests minify a module, import both the original and the minified version, run them, and compare the results. What DOES change: local variable names (unless you turn that off), constant expressions that can be worked out in advance, and dead code. Anything depending on a function's name at runtime, or on Function.prototype.toString, can break under mangling — turn mangling off if you rely on either.

Whether your code is parsed as an ES module or as a plain script. Modules can use import and export and are always in strict mode. It is on by default because that is what most modern code is; if your file is an old-style script that uses "with" or relies on non-strict behaviour, turn it off.

For production, usually yes — they are noise, and they can leak internal detail to anyone who opens the developer tools. It is off by default because silently deleting code is not something a tool should do without being asked.

Yes, by default. Comments beginning /*! and comments containing @license or @preserve are kept, because stripping them from someone else's MIT-licensed library is a licence violation. Ordinary comments are removed.

Not on this page. A source map is only useful next to the original file at a known URL, which does not fit a paste-and-copy tool — your build tool is the right place for that.

terser 5.51.2, BSD-2-Clause licensed, served from this site rather than a CDN and downloaded only when you open this page.