Postcss-prefix-selector NPM

postcss-prefix-selector

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

Install

$ npm install postcss-prefix-selector

Usage with PostCSS

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

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

const out = postcss().use(prefixer({
  prefix: '.some-selector',
  exclude: ['.c'],

  // 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

Using the options above and the CSS below...

body {
  background: red;
}

.a, .b {
  color: aqua;
}

.c {
  color: coral;
}

You will get the following output

body.some-selector {
  background: red;
}

.some-selector .a, .some-selector .b {
  color: aqua;
}

.c {
  color: coral;
}

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']
              }
            }
          }
        }
      }
    ]
  }]
}

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