postcss-prefix-selector

Prefix every CSS selector with a custom namespace .a => .prefix .a

Table of Contents

• Install
• Usage with PostCSS
• Usage with Webpack
• Usage with Vite
• Options
• Maintainer
• Contribute
• License

Install

$ npm install postcss-prefix-selector

Usage with PostCSS

A prefix is added before most selectors. Below is an example of how CSS will be transformed by adding a prefix called .namespace.

const prefixer = require('postcss-prefix-selector')

// css to be processed
const css = fs.readFileSync("input.css", "utf8")

const out = postcss().use(prefixer({
  prefix: '.namespace',
  exclude: ['.c'],
})).process(css).css

/* Input */
.a, .b {
  color: aqua;
}

.c {
  color: coral;
}

/* Output */
.namespace .a, .namespace .b {
  color: aqua;
}

.c {
  color: coral;
}

Please note that global selectors (html, body, :root) cannot be prefixed so instead they will be replaced with the prefix. This behaviour can be disabled with the skipGlobalSelectors option.

/* Input */
:root { --bs-blue:#0d6efd; }
html { padding: 0; }
body { margin: 0; }

/* Output */
.namespace { --bs-blue:#0d6efd; }
.namespace { padding: 0; }
.namespace { margin: 0; }

It's also possible to customize the way prefixing is done by defining a transform function:

const out = postcss().use(prefixer({
  prefix: '.namespace',
  // Optional transform callback for case-by-case overrides
  transform: function (prefix, selector, prefixedSelector, filePath, rule) {
    if (selector === 'body') {
      return 'body' + prefix;
    } else {
      return prefixedSelector;
    }
  }
})).process(css).css

/* Input */
body {
  background: red;
}

/* Output */
body.namespace {
  background: red;
}

Usage with webpack

Use it like you'd use any other PostCSS plugin. If you also have autoprefixer in your webpack config then make sure that postcss-prefix-selector is called first. This is needed to avoid running the prefixer twice on both standard selectors and vendor specific ones (ex: @keyframes and @webkit-keyframes).

module: {
  rules: [{
    test: /\.css$/,
    use: [
      require.resolve('style-loader'),
      require.resolve('css-loader'),
      {
        loader: require.resolve('postcss-loader'),
        options: {
          postcssOptions: {
            plugins: {
              "postcss-prefix-selector": {
                prefix: '.my-prefix',
                transform(prefix, selector, prefixedSelector, filePath, rule) {
                  if (selector.match(/^(html|body)/)) {
                    return selector.replace(/^([^\s]*)/, `$1 ${prefix}`);
                  }
                  
                  if (filePath.match(/node_modules/)) {
                    return selector; // Do not prefix styles imported from node_modules
                  }
                  
                  const annotation = rule.prev();
                  if (annotation?.type === 'comment' && annotation.text.trim() === 'no-prefix') {
                    return selector; // Do not prefix style rules that are preceded by: /* no-prefix */
                  }

                  return prefixedSelector;
                },
              },
              autoprefixer: {
                browsers: ['last 4 versions']
              }
            }
          }
        }
      }
    ]
  }]
}

Usage with Vite

Following the same way of Webpack but for Vite:

import prefixer from 'postcss-prefix-selector';
import autoprefixer from 'autoprefixer';

...

export default defineConfig({
...
  css: {
    postcss: {
      plugins: [
        prefixer({
          prefix: '.my-prefix',
          transform(prefix, selector, prefixedSelector, filePath, rule) {
            if (selector.match(/^(html|body)/)) {
              return selector.replace(/^([^\s]*)/, `$1 ${prefix}`);
            }

            if (filePath.match(/node_modules/)) {
              return selector; // Do not prefix styles imported from node_modules
            }

            const annotation = rule.prev();
            if (annotation?.type === 'comment' && annotation.text.trim() === 'no-prefix') {
              return selector; // Do not prefix style rules that are preceded by: /* no-prefix */
            }

            return prefixedSelector;
          },
        }),

        autoprefixer({}) // add options if needed
      ],
    }
  },
...
});  

Options

Name	Type	Description
prefix	string	This string is added before every CSS selector
exclude	string[] or RegExp[]	It's possible to avoid prefixing some selectors by passing an array of selectors
transform	Function	In cases where you may want to use the prefix differently for different selectors, it is possible to pass in a custom transform method
ignoreFiles	string[] or RegExp[]	List of ignored files for processing
includeFiles	string[] or RegExp[]	List of included files for processing
skipGlobalSelectors	boolean	When enabled, global selectors (html, body, root) won't be modified by the prefixer. Default: false.

Maintainer

This project was originally created by @jongleberry and is being maintained by @RadValentin. If you have any questions, feel free to ping the latter.

Contribute

Please contribute! If you have any questions or bugs, open an issue. Or, open a pull request with a fix.

This project uses Mocha. If you submit a PR, please add appropriate tests and make sure that everything is green for your branch.

License

MIT © 2015-2024 Jonathan Ong.