Question

Loader for webpack to process CSS with PostCSS

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Install

npm i -D postcss-loader

Usage

postcss.config.js

module.exports = {
  parser: 'sugarss',
  plugins: {
    'postcss-import': {},
    'postcss-cssnext': {},
    'cssnano': {}
  }
}

You can read more about common PostCSS Config here.

Config Cascade

You can use different postcss.config.js files in different directories. Config lookup starts from path.dirname(file) and walks the file tree upwards until a config file is found.

|– components
| |– component
| | |– index.js
| | |– index.png
| | |– style.css (1)
| | |– postcss.config.js (1)
| |– component
| | |– index.js
| | |– image.png
| | |– style.css (2)
|
|– postcss.config.js (1 && 2 (recommended))
|– webpack.config.js
|
|– package.json

After setting up your postcss.config.js, add postcss-loader to your webpack.config.js. You can use it standalone or in conjunction with css-loader (recommended). Use it after css-loader and style-loader, but before other preprocessor loaders like e.g sass|less|stylus-loader, if you use any.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ 'style-loader', 'postcss-loader' ]
      }
    ]
  }
}

⚠️ When postcss-loader is used standalone (without css-loader) don't use @import in your CSS, since this can lead to quite bloated bundles

webpack.config.js (recommended)

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          { loader: 'css-loader', options: { importLoaders: 1 } },
          'postcss-loader'
        ]
      }
    ]
  }
}

Options

Name	Type	Default	Description
exec	{Boolean}	undefined	Enable PostCSS Parser support in CSS-in-JS
parser	`{String\	Object}`	undefined	Set PostCSS Parser
syntax	`{String\	Object}`	undefined	Set PostCSS Syntax
stringifier	`{String\	Object}`	undefined	Set PostCSS Stringifier
config	{Object}	undefined	Set postcss.config.js config path && ctx
plugins	`{Array\	Function}`	[]	Set PostCSS Plugins
sourceMap	`{String\	Boolean}`	false	Enable Source Maps

Exec

If you use JS styles without the postcss-js parser, add the exec option.

{
  test: /\.style.js$/,
  use: [
    'style-loader',
    { loader: 'css-loader', options: { importLoaders: 1 } },
    { loader: 'postcss-loader', options: { parser: 'sugarss', exec: true } }
  ]
}

Config

Name	Type	Default	Description
path	{String}	undefined	PostCSS Config Path
context	{Object}	undefined	PostCSS Config Context

Path

You can manually specify the path to search for your config (postcss.config.js) with the config.path option. This is needed if you store your config in a separate e.g ./config || ./.config folder.

⚠️ Otherwise it is unnecessary to set this option and is not recommended

webpack.config.js

{
  loader: 'postcss-loader',
  options: {
    config: {
      path: 'path/to/postcss.config.js'
    }
  }
}

Context (ctx)

Name	Type	Default	Description
env	{String}	'development'	process.env.NODE_ENV
file	{Object}	loader.resourcePath	extname, dirname, basename
options	{Object}	{}	Options

postcss-loader exposes context ctx to the config file, making your postcss.config.js dynamic, so can use it to do some real magic ✨

postcss.config.js

module.exports = ({ file, options, env }) => ({
  parser: file.extname === '.sss' ? 'sugarss' : false,
  plugins: {
    'postcss-import': { root: file.dirname },
    'postcss-cssnext': options.cssnext ? options.cssnext : false,
    'autoprefixer': env == 'production' ? options.autoprefixer : false,
    'cssnano': env === 'production' ? options.cssnano : false
  }
})

webpack.config.js

{
  loader: 'postcss-loader',
  options: {
    config: {
      ctx: {
        cssnext: {...options},
        cssnano: {...options},
        autoprefixer: {...options}
      }
    }
  }
}

Plugins

webpack.config.js

{
  loader: 'postcss-loader',
  options: {
    ident: 'postcss',
    plugins: (loader) => [
      require('postcss-import')({ root: loader.resourcePath }),
      require('postcss-cssnext')(),
      require('autoprefixer')(),
      require('cssnano')()
    ]
  }
}

⚠️ webpack requires an identifier (ident) in options when {Function}/require is used (Complex Options). The ident can be freely named as long as it is unique. It's recommended to name it (ident: 'postcss')

Syntaxes

Name	Type	Default	Description
parser	`{String\	Function}`	undefined	Custom PostCSS Parser
syntax	`{String\	Function}`	undefined	Custom PostCSS Syntax
stringifier	`{String\	Function}`	undefined	Custom PostCSS Stringifier

Parser

webpack.config.js

{
  test: /\.sss$/,
  use: [
    ...,
    { loader: 'postcss-loader', options: { parser: 'sugarss' } }
  ]
}

Syntax

webpack.config.js

{
  test: /\.css$/,
  use: [
    ...,
    { loader: 'postcss-loader', options: { syntax: 'sugarss' } }
  ]
}

Stringifier

webpack.config.js

{
  test: /\.css$/,
  use: [
    ...,
    { loader: 'postcss-loader', options: { stringifier: 'midas' } }
  ]
}

SourceMap

Enables source map support, postcss-loader will use the previous source map given by other loaders and update it accordingly, if no previous loader is applied before postcss-loader, the loader will generate a source map for you.

:warning: If a previous loader like e.g sass-loader is applied and it's sourceMap option is set, but the sourceMap option in postcss-loader is omitted, previous source maps will be discarded by postcss-loader entirely.

webpack.config.js

{
  test: /\.css/,
  use: [
    { loader: 'style-loader', options: { sourceMap: true } },
    { loader: 'css-loader', options: { sourceMap: true } },
    { loader: 'postcss-loader', options: { sourceMap: true } },
    { loader: 'sass-loader', options: { sourceMap: true } }
  ]
}

'inline'

You can set the sourceMap: 'inline' option to inline the source map within the CSS directly as an annotation comment.

webpack.config.js

{
  loader: 'postcss-loader',
  options: {
    sourceMap: 'inline'
  }
}

.class { color: red; }

/*# sourceMappingURL=data:application/json;base64, ... */

Examples

Stylelint

webpack.config.js

{
  test: /\.css$/,
  use: [
    'style-loader',
    'css-loader',
    {
      loader: 'postcss-loader',
      options: {
        ident: 'postcss',
        plugins: [
          require('postcss-import')(),
          require('stylelint')(),
          ...,
        ]
      }
    }
  ]
}

CSS Modules

This loader cannot be used with CSS Modules out of the box due to the way css-loader processes file imports. To make them work properly, either add the css-loader’s importLoaders option.

webpack.config.js

{
  test: /\.css$/,
  use: [
    'style-loader',
    { loader: 'css-loader', options: { modules: true, importLoaders: 1 } },
    'postcss-loader'
  ]
}

or use postcss-modules instead of css-loader.

CSS-in-JS

If you want to process styles written in JavaScript, use the postcss-js parser.

{
  test: /\.style.js$/,
  use: [
    'style-loader',
    { loader: 'css-loader', options: { importLoaders: 2 } },
    { loader: 'postcss-loader', options: { parser: 'postcss-js' } },
    'babel-loader'
  ]
}

As result you will be able to write styles in the following way

import colors from './styles/colors'

export default {
    '.menu': {
      color: colors.main,
      height: 25,
      '&_link': {
      color: 'white'
    }
  }
}

:warning: If you are using Babel you need to do the following in order for the setup to work

1. Add babel-plugin-add-module-exports to your configuration
2. You need to have only one default export per style module

Extract CSS

webpack.config.js

const ExtractTextPlugin = require('extract-text-webpack-plugin')

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ExtractTextPlugin.extract({
          fallback: 'style-loader',
          use: [
            { loader: 'css-loader', options: { importLoaders: 1 } },
            'postcss-loader'
          ]
        })
      }
    ]
  },
  plugins: [
    new ExtractTextPlugin('[name].css')
  ]
}