postcss-deadcss

PostCSS plugin that helps to find dead css in a project.

Implements technique from https://csswizardry.com/2018/01/finding-dead-css/

/* Input example */
.foo {
    color: red;
}

/* Output example */
.foo {
    background-image: url('https://monitoring.host/pixel.png?.foo');
    color: red;
}

Usage

Step 1: Install plugin:

npm install --save-dev postcss postcss-deadcss

Step 2: Check you project for existed PostCSS config: postcss.config.js in the project root, "postcss" section in package.json or postcss in bundle config.

If you do not use PostCSS, add it according to official docs and set this plugin in settings. Alternatively, you can use the postcss-cli to run postcss-deadcss from CLI:

npm install postcss-cli

# after configuration:
npx postcss *.css -d output/

See npx postcss -h for help.

Step 3: Add the plugin to plugins list:

module.exports = {
  plugins: [
    require('autoprefixer'),
+   require('postcss-deadcss')({
+     url: 'https://monitoring.host/pixel.png',
+     hash: true,
+   }),
  ]
}

Available options:

Name	Type	Default	Description
url	string	'https://monitoring.host/pixel.png'	Base url with transparent image to load
hash	boolean	false	To use md5 hashes of seloctors for background image urls, otherwise to use URL ecoded selectors
append	boolean	false	To append background-image declaration instead of prepend it (this will break styling during testing, but is not required manual checks if background-image has been overwritten by other declaration below in the same rule or not)

Step 4: Deploy css and transparent image and start monitoring requests to the image. After considered amount of time you can remove css rules that hasn't been requested or rewrite code when css rules are used too unfrequently. Enjoy the results! 🎉