JS minifier

What each checkbox changes

One file, four settings, measured

This is the Load sample input: 763 bytes with a license banner, comments and normal indentation.

/*! cart-total v1.2.0 | MIT */

// Format a number of cents as a price string.
function formatPrice(cents, currency) {
  const amount = cents / 100;
  return new Intl.NumberFormat("en-US", {
    style: "currency",
    currency: currency || "USD"
  }).format(amount);
}

/* Sum line items, skipping anything with a bad quantity. */
function cartTotal(items) {
  let total = 0;
  for (const item of items) {
    if (!Number.isFinite(item.qty) || item.qty <= 0) {
      continue;
    }
    total += item.priceCents * item.qty;
  }
  return total;
}

const items = [
  { sku: "TEA-01", priceCents: 1250, qty: 2 },
  { sku: "MUG-07", priceCents: 1800, qty: 1 },
  { sku: "BAD-00", priceCents: 999, qty: -1 }
];

console.log(`Total: ${formatPrice(cartTotal(items))}`);

With the defaults (Compress, Mangle and Keep license on, ES module off), Terser 5.51.2 returns 451 bytes:

/*! cart-total v1.2.0 | MIT */
function formatPrice(t,e){const r=t/100;return new Intl.NumberFormat("en-US",{style:"currency",currency:e||"USD"}).format(r)}function cartTotal(t){let e=0;for(const r of t)!Number.isFinite(r.qty)||r.qty<=0||(e+=r.priceCents*r.qty);return e}const items=[{sku:"TEA-01",priceCents:1250,qty:2},{sku:"MUG-07",priceCents:1800,qty:1},{sku:"BAD-00",priceCents:999,qty:-1}];console.log(`Total: ${formatPrice(cartTotal(items))}`);

The for loop with its if and continue became one || chain, and cents, currency, amount became single letters. Both versions print Total: $43.00. Here is the same input under each setting, measured in UTF-8 bytes. The gzip column is what this page's own counter reported in Chrome:

The gap between raw bytes and gzip bytes matters. Raw savings look dramatic because indentation and comments compress well anyway. If the page is served with gzip or Brotli, the real transfer saving with the defaults is 127 bytes, not the 312 that the raw count suggests.

Why top-level names stay long

In the defaults row, formatPrice, cartTotal and items keep their full names. That is deliberate. In a classic script, a top-level function or var becomes a property of the global object, and some other script tag, an inline onclick, or the console might call it by name. Renaming it would break those callers, and the minifier cannot see them.

Ticking ES module removes that guarantee. In the module row, Terser inlined both functions straight into the console.log call, because nothing outside the file can reach them. That is correct for a real module and wrong for a script that exposes helpers. If you want both small output and a public API, wrap the file in a function yourself and assign only the public names to window.

Newlines that already changed your code

Minifiers delete line breaks, which makes people worry that automatic semicolon insertion will bite. Terser parses first, so it never adds an ASI bug. What it does is show you one that was already there. Feed it this, with Compress and Mangle off:

let total = price
(discount || 0).toFixed(2)

and you get let total=price(discount||0).toFixed(2);. That is not the minifier joining two lines. JavaScript never inserted a semicolon after price, so the original was always a call to price. The same happens when a line starts with [ or a backtick. While testing this page, two of our own test snippets failed in exactly this way before minification. If a result looks like it merged two statements, put a semicolon at the end of the first line in your source and run it again.

Where this tool stops

• It minifies one file. It does not follow import or require, combine files, or remove unused exports across a project. That is a bundler's job (esbuild, Rollup, webpack, Vite).
• No source maps are produced. Keep your original file next to the minified one, or stack traces from production will point at column 3,000 of line 1.
• Property names, object keys and string contents are left alone, so long API field names stay long.
• Code that inspects itself can break: Function.prototype.toString, eval that refers to local names, or fn.name checks. Untick Mangle for those files.
• Large inputs work but take a moment. A 57 KB library took about a quarter of a second in our Node test. Very large bundles are better handled by a build step.

For the rest of the page, the CSS minifier shrinks stylesheets the same way and the HTML formatter can minify markup. To turn a minified snippet into a bookmarklet, prefix it with javascript: and run it through the URL encoder.

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