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JavaScript Minifier

Compress and minify JavaScript using Terser — with variable mangling, dead-code removal, and size stats.

Last updated: March 25, 2026

Client-Side Processing
Input Data Stays on Device
Instant Local Execution

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What is JavaScript Minifier?

JavaScript minification is the most impactful single optimization for web performance. Unlike images (which require quality trade-offs) or HTML (small gains), JavaScript minification routinely reduces file sizes by 30–70% with zero functional change. It works by removing whitespace and comments, shortening local variable and function names to single letters (mangling), removing dead code branches, and simplifying constant expressions — entirely automatically.

This tool uses Terser, the industry-standard JavaScript minifier used internally by Vite, Webpack, Rollup, Parcel, and esbuild. It supports modern JavaScript syntax including ES2022 (class fields, top-level await), JSX-free TypeScript syntax, and ECMAScript modules. Unlike older tools like UglifyJS (ES5 only), Terser handles arrow functions, destructuring, optional chaining, and all modern JavaScript patterns correctly.

How to Use JavaScript Minifier

1

Paste your JavaScript code into the input area on the left

2

Select a compression level: Safe (whitespace + comments only), Standard (+ mangling), Aggressive (+ dead code removal)

3

Click "Minify" to run Terser and see the compressed output

4

Review the compression stats: original size, minified size, and percentage saved

5

Click "Copy" to copy the minified JS, or "Download .js" to save it as a file

Common Use Cases

  • Compressing vanilla JavaScript files before serving from a CDN or static host
  • Reducing the size of third-party library customizations or patches
  • Minifying standalone scripts (analytics snippets, embed widgets) before distribution
  • Quick benchmarking of how much JS size a specific code pattern adds
  • Compressing a polyfill file before including it in a legacy support bundle
  • Minifying utility scripts embedded in WordPress themes or plugins
  • Reducing the size of JavaScript served in a <script> tag inline in HTML
  • Validating that a specific Terser configuration produces the expected output

Example Input and Output

A readable utility function minified to a single optimized line:

Original JavaScript (312 bytes)
/**
 * Formats a number with thousands separators
 * @param {number} num - The number to format
 * @returns {string} Formatted number string
 */
function formatNumber(num) {
    if (typeof num !== 'number' || isNaN(num)) {
        return '0';
    }
    return num.toLocaleString('en-US');
}
Minified with Terser standard mode (87 bytes — 72% smaller)
function formatNumber(n){return"number"!=typeof n||isNaN(n)?"0":n.toLocaleString("en-US")}

Privacy First

All JavaScript minification runs in your browser using Terser (compiled to WebAssembly). Your source code — including any API keys, business logic, or internal algorithms — is never transmitted to our servers.

Use Source Maps in Production

When using minified JavaScript in production, always generate source maps alongside it. Source maps let browser DevTools show original, readable code when debugging errors — while serving the minified file to end users. Build tools like Vite generate source maps automatically.

ES Module Compatibility

This tool supports modern ESM syntax (import/export, dynamic import()). However, it does not bundle modules — it minifies a single file. If your code uses ES module imports, bundle with esbuild or Rollup first, then optionally run through Terser for final compression.

Frequently Asked Questions

What is the difference between minification and obfuscation?
Minification removes whitespace and shortens names to reduce file size — the logic remains readable if reformatted. Obfuscation intentionally transforms code to make it very hard to understand (renaming to nonsense, encoding strings, adding junk code). Minification is for performance; obfuscation is for (imperfect) code protection. This tool performs minification + optional mangling, not full obfuscation.
What does "mangling" mean in JavaScript minification?
Mangling renames local variables, function parameters, and class fields from descriptive names to single characters (firstName → a, calculateTotal → b). This significantly reduces file size. Mangling is safe for local scope names because they are only used within the function. Global names (window.myFunction, module.exports) are never mangled since external code depends on them.
Will minification break my JavaScript?
Not for correctly written JavaScript. Known edge cases: (1) code that reads function.name or variable.name for reflection, (2) code that uses arguments.callee (deprecated strict mode violation), (3) eval() with string code that references local variable names (extremely rare). These patterns are already considered bad practice and should not appear in modern code.
How much size reduction should I expect?
20–50% for typical application JavaScript with standard settings. 50–70% for heavily commented utility libraries. Files that are already minified will see minimal improvement. The largest gains come from removing comments, mangling long variable names, and collapsing small functions.
Should I minify JavaScript manually or use a build tool?
For production applications, always use an automated build tool (Vite, Webpack, Parcel, esbuild) that minifies as part of the build pipeline. This tool is best for: WordPress/theme scripts without a build step, standalone utility scripts, CDN-hosted custom code, and quick checks to verify minification output.
What is dead code elimination?
Dead code is code that can never execute — for example, code after a return statement, or an if (false) block, or a function that is never called. Terser identifies and removes dead code branches during the "compress" pass. This is separate from tree-shaking (which is module-level dead code removal performed by bundlers at the import level).

How This Tool Works

The JavaScript source is passed to Terser running as a WebAssembly module in the browser. Terser performs a multi-pass compression pipeline: (1) parse the JS into an AST (Abstract Syntax Tree), (2) compress: fold constants, remove dead code, simplify boolean expressions, inline single-use variables, (3) mangle: rename local identifiers, (4) generate: serialize the optimized AST to a compact string without non-essential whitespace. All passes run synchronously in-browser with no network calls.

Technical Stack

Terser (WASM)AST-based compressionVariable manglingDead code eliminationClient-side only

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