Unminified JavaScript

Detects unminified JavaScript that could be optimized

What it detects

Unminified JavaScript, based on newline ratio, comment volume, identifier length, indentation, and whitespace. Preserved /*! ... */ and //! license banners (the standard “keep on minify” convention used by Terser, esbuild, Vite, and Webpack) are stripped before analysis, so a fully minified bundle that legitimately retains license comments is not flagged.

Comment counting is string aware. The // in a URL such as "https://example.com", and comment openers inside single-quoted, double-quoted and template literals, are not counted as comments, so a minified bundle that ships URLs is not reported as unminified with an inflated savings estimate.

Regular expression literals are recognised heuristically rather than parsed. A / is read as the start of a regex after an operator, after a keyword such as return or typeof, and after the ) of an if, while or for head. In rarer positions, such as directly after another ) or ], it is read as division instead, and the regex body is scanned as ordinary code. A regex used directly as the left operand of / or *, as in /a/*2, is also read as division, since dividing or multiplying by a regular expression is not something real code does. Both cases are rare, and neither affects whether ordinary minified output is flagged. Shebang lines (#!) and Annex B <!-- comments are not counted.

Solution

Minify JavaScript to reduce file size and improve load times. Use build tools like Terser, esbuild, or UglifyJS. Most bundlers (Webpack, Vite, Rollup) minify automatically in production. Minification shortens variable names, removes whitespace, and dead code.

Options

This rule supports the following configuration options:

Configuration example

[rules."perf/unminified-js"]
min_size_bytes = undefined

Enable / disable

Disable this rule

[rules]
disable = ["perf/unminified-js"]

Disable all Performance rules

[rules]
disable = ["perf/*"]

Enable only this rule

[rules]
enable = ["perf/unminified-js"]
disable = ["*"]