JavaScript Minifier

A note on this tool

This is a basic whitespace-and-comment minifier: it strips comments and collapses whitespace while leaving strings and template literals untouched and keeping line breaks where automatic semicolon insertion could depend on them. It does not fully parse JavaScript, so unusual code (for example, some regex literals) can still be mishandled — always test the output. It does no variable renaming or dead-code elimination; for production code, use a real parser-based minifier such as Terser.

How to use the JavaScript Minifier

1. Paste your JavaScript into the input box.
2. Click Minify to strip comments and collapse whitespace.
3. Test the output before using it, especially for scripts with regex literals or complex template strings.

Common use cases

• Shrinking a small standalone script for a static site with no build step
• Quickly seeing how much comments and formatting add to a file's size
• Cleaning up a script before pasting it into a size-constrained field

Worked example

Paste in a small utility function written with generous spacing and inline comments explaining each step, and minifying strips the comments and collapses the whitespace down to a single dense line — for a typical 40-line helper function, that's often a 30–50% size reduction from formatting removal alone, before any variable renaming or dead-code elimination that a full build-tool minifier would additionally apply.

Things to watch out for

This tool performs basic, surface-level minification (removing comments and collapsing whitespace) rather than the more aggressive transformations a build-tool minifier like Terser or UglifyJS performs — those tools also rename local variables to shorter names and can eliminate genuinely unreachable code, producing a meaningfully smaller file for a large production bundle. For a quick one-off script, or code with no build pipeline attached to it at all, this level of minification is enough; for a production JavaScript bundle serving real traffic, route it through a proper build step instead. Always keep the original, readable source as your file to edit — never edit the minified output directly, since a single missing semicolon in dense minified code is far harder to spot and fix.

Code that breaks when minified: our tests

We ran small snippets through the tool's exact rules and executed the before and after versions in Node.js. These patterns produced broken output:

• Code without semicolons. Lines are joined with a space, so let a = 1 on one line and let b = 2 on the next become let a=1 let b=2, a syntax error (Unexpected identifier). JavaScript's automatic semicolon insertion depended on those line breaks.
• A plus or minus sign before a variable. Spaces around + and - are removed, so x + +y becomes x++y and x - -y becomes x--y, which the engine reads as increment and decrement operators.
• // inside a string or regex. Everything after // is treated as a comment unless the // comes right after a colon. "https://x.com" survives, but "https://x.com//path" and "a // b" are cut off.

Changes inside strings

Some output runs but behaves differently. Spaces next to = , : ; ( ) { } and the operators are removed everywhere, including inside quotes, so console.log("a = b, c") prints a=b,c after minifying. Template literals lose their line breaks and indentation: a two-line template string becomes one line joined by a single space. If your code builds messages, HTML or SQL from strings, compare the output carefully.

How to check the output quickly

1. Save the result as a file and run node --check file.js. Node.js parses the file without running it and reports the first syntax error with its position.
2. Load the page that uses the script and open the browser console. A syntax error stops the whole file, so one error is enough to break every feature in it.
3. Exercise anything that prints text, because string changes do not cause errors.

Code written with a semicolon at the end of every statement, with no // inside strings and no spaced-out + + or - -, ran the same before and after in the cases we tested. For anything else, a parser-based tool such as Terser is the safer choice. For other quick jobs that run in the browser, see our roundup of browser tools for developers.