JavaScript Minifier: Strip Comments and Whitespace Safely

A JavaScript minifier is a tool that makes a script smaller without changing what it does, by removing characters the browser does not need: comments, indentation and spaces between tokens. This one runs in your browser, leaves every name and string untouched, and shows the bytes saved.

How This JavaScript Minifier Works

The tool reads your code one token at a time (a word, a number, a string, an operator) and copies each token unchanged. It only decides what goes between two tokens: nothing, a single space, or a single line break. Because strings, template literals and regex literals are whole tokens, text such as "http://a//b" or /https?:\/\// is never mistaken for a comment.

Worked Example: Before and After

Press Load Example above to reproduce this. The input has no semicolons, a URL inside a string, a regex with slashes and a template literal that looks like it contains a comment.

// Greeting helper
function greet(name) {
  /* Say hello */
  var site = "https://example.com/a//b";   // not a comment
  var isUrl = /^https?:\/\//.test(site)
  console.log(`Hello,   ${name}!  // still text`, site, isUrl)
}

greet("World")

Output:

function greet(name){var site="https://example.com/a//b";var isUrl=/^https?:\/\//.test(site)
console.log(`Hello,   ${name}!  // still text`,site,isUrl)}
greet("World")

Both versions print the same line when run. The two comments and the indentation are gone, the string, regex and template are untouched, and two line breaks remain because the statements before them have no semicolon.

How Much Smaller? Measured Results

The saving depends on how many comments and how much indentation a file has; code that is already compact shrinks very little. In October 2026 we ran 6,202 open-source JavaScript files (47.9 MB in total) through this minifier and parsed every result: each file produced the same syntax tree as its original, and the total size fell by 38.8%. The test file was also run with Node.js before and after minifying and printed identical output.

Limits: What This Tool Does Not Do

• No renaming or code removal. It does not shorten variable names, drop unused code or rewrite expressions, so a parser-based minifier in a build pipeline will produce smaller files.
• It is a tokenizer, not a full parser. It tells a regex from a division by the token before the slash. Unusual code, such as a division written directly after a closing brace, can be misread, so run your tests on the output.
• Plain JavaScript only. JSX and TypeScript-only syntax are not supported.
• The output can have several lines. Line breaks that may end a statement are kept on purpose; each costs one byte, the same as a semicolon.

After minifying, the tool checks that the result still parses whenever your input parses as a classic script, and shows the outcome next to the byte counts. Files that use import or export are minified the same way, but that check is skipped for them.

Why Minify JavaScript?

Chrome's Lighthouse documentation describes minification as "the process of removing whitespace and any code that is not necessary to create a smaller but perfectly valid code file", and Lighthouse has a "Minify JavaScript" audit that lists unminified files with the potential saving (Chrome for Developers). Smaller files download faster. Servers usually compress JavaScript with gzip or Brotli as well; the two stack, as the gzip row in the table shows. All processing here happens in your browser, so the code you paste is never sent to a server.

Last updated: October 2026