# postcss-prefix-selector

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

## Table of Contents

- [Install](#install)
- [Usage with PostCSS](#usage-with-postcss)
- [Usage with Webpack](#usage-with-webpack)
- [Options](#options)
- [Maintainer](#maintainer)
- [Contribute](#contribute)
- [License](#license)

## Install

```console
$ npm install postcss-prefix-selector
```

## Usage with PostCSS

```js
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...

```css
body {
  background: red;
}

.a, .b {
  color: aqua;
}

.c {
  color: coral;
}
```

You will get the following output

```css
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`).

```js
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 |

## Maintainer

This project was originally created by [@jongleberry](https://github.com/jonathanong) and is being maintained by [@RadValentin](https://github.com/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](https://github.com/RadValentin/postcss-prefix-selector/issues/new). 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](LICENSE) © 2015-2022 Jonathan Ong.

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