CSS Loader

css-loader

The css-loader interprets @import and url() like import/require() and will resolve them.

Requirements

This module requires a minimum of Node v6.9.0 and Webpack v4.0.0.

Getting Started

To begin, you'll need to install css-loader:

npm install --save-dev css-loader

Then add the plugin to your webpack config. For example:

file.js

import css from 'file.css';

webpack.config.js

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

Good loaders for requiring your assets are the file-loader and the url-loader which you should specify in your config (see below).

And run webpack via your preferred method.

`toString`

You can also use the css-loader results directly as a string, such as in Angular's component style.

webpack.config.js

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

const css = require('./test.css').toString();

console.log(css); // {String}

If there are SourceMaps, they will also be included in the result string.

If, for one reason or another, you need to extract CSS as a plain string resource (i.e. not wrapped in a JS module) you might want to check out the extract-loader. It's useful when you, for instance, need to post process the CSS as a string.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'handlebars-loader', // handlebars loader expects raw resource string
          'extract-loader',
          'css-loader',
        ],
      },
    ],
  },
};

Options

Name	Type	Default	Description
`url`	`{Boolean\|Function}`	`true`	Enable/Disable `url()` handling
`import`	`{Boolean\/Function}`	`true`	Enable/Disable @import handling
`modules`	`{Boolean\|String}`	`false`	Enable/Disable CSS Modules and setup mode
`localIdentName`	`{String}`	`[hash:base64]`	Configure the generated ident
`sourceMap`	`{Boolean}`	`false`	Enable/Disable Sourcemaps
`camelCase`	`{Boolean\|String}`	`false`	Export Classnames in CamelCase
`importLoaders`	`{Number}`	`0`	Number of loaders applied before CSS loader
`exportOnlyLocals`	`{Boolean}`	`false`	Export only locals

`url`

Type: Boolean|Function Default: true

Control url() resolving. Absolute urls are not resolving.

Examples resolutions:

url(image.png) => require('./image.png')
url('image.png') => require('./image.png')
url(./image.png) => require('./image.png')
url('./image.png') => require('./image.png')
url('http://dontwritehorriblecode.com/2112.png') => require('http://dontwritehorriblecode.com/2112.png')
image-set(url('image2x.png') 1x, url('image1x.png') 2x) => require('./image1x.png') and require('./image2x.png')

To import assets from a node_modules path (include resolve.modules) and for alias, prefix it with a ~:

url(~module/image.png) => require('module/image.png')
url('~module/image.png') => require('module/image.png')
url(~aliasDirectory/image.png) => require('otherDirectory/image.png')

`Boolean`

Enable/disable url() resolving.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          url: true,
        },
      },
    ],
  },
};

`Function`

Allow to filter url(). All filtered url() will not be resolved (left in the code as they were written).

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          url: (url, resourcePath) => {
            // resourcePath - path to css file

            // `url()` with `img.png` stay untouched
            return url.includes('img.png');
          },
        },
      },
    ],
  },
};

`import`

Type: Boolean Default: true

Control @import resolving. Absolute urls in @import will be moved in runtime code.

Examples resolutions:

@import 'style.css' => require('./style.css')
@import url(style.css) => require('./style.css')
@import url('style.css') => require('./style.css')
@import './style.css' => require('./style.css')
@import url(./style.css) => require('./style.css')
@import url('./style.css') => require('./style.css')
@import url('http://dontwritehorriblecode.com/style.css') => @import url('http://dontwritehorriblecode.com/style.css') in runtime

To import styles from a node_modules path (include resolve.modules) and for alias, prefix it with a ~:

@import url(~module/style.css) => require('module/style.css')
@import url('~module/style.css') => require('module/style.css')
@import url(~aliasDirectory/style.css) => require('otherDirectory/style.css')

`Boolean`

Enable/disable @import resolving.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          import: true,
        },
      },
    ],
  },
};

`Function`

Allow to filter @import. All filtered @import will not be resolved (left in the code as they were written).

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          import: (parsedImport, resourcePath) => {
            // parsedImport.url - url of `@import`
            // parsedImport.media - media query of `@import`
            // resourcePath - path to css file

            // `@import` with `style.css` stay untouched
            return parsedImport.url.includes('style.css');
          },
        },
      },
    ],
  },
};

`modules`

Type: Boolean|String Default: false

The modules option enables/disables the CSS Modules spec and setup basic behaviour.

Name	Type	Description
`true`	`{Boolean}`	Enables local scoped CSS by default (use local mode by default)
`false`	`{Boolean}`	Disable the CSS Modules spec, all CSS Modules features (like `@value`, `:local`, `:global` and `composes`) will not work
`'local'`	`{String}`	Enables local scoped CSS by default (same as `true` value)
`'global'`	`{String}`	Enables global scoped CSS by default

Using false value increase performance because we avoid parsing CSS Modules features, it will be useful for developers who use vanilla css or use other technologies.

You can read about modes below.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          modules: true,
        },
      },
    ],
  },
};

`Scope`

Using local value requires you to specify :global classes. Using global value requires you to specify :local classes.

You can find more information here.

Styles can be locally scoped to avoid globally scoping styles.

The syntax :local(.className) can be used to declare className in the local scope. The local identifiers are exported by the module.

With :local (without brackets) local mode can be switched on for this selector. The :global(.className) nocation can be used to declare an explicit global selector. With :global (without brackets) global mode can be switched on for this selector.

The loader replaces local selectors with unique identifiers. The chosen unique identifiers are exported by the module.

:local(.className) {
  background: red;
}
:local .className {
  color: green;
}
:local(.className .subClass) {
  color: green;
}
:local .className .subClass :global(.global-class-name) {
  color: blue;
}

._23_aKvs-b8bW2Vg3fwHozO {
  background: red;
}
._23_aKvs-b8bW2Vg3fwHozO {
  color: green;
}
._23_aKvs-b8bW2Vg3fwHozO ._13LGdX8RMStbBE9w-t0gZ1 {
  color: green;
}
._23_aKvs-b8bW2Vg3fwHozO ._13LGdX8RMStbBE9w-t0gZ1 .global-class-name {
  color: blue;
}

ℹ️ Identifiers are exported

exports.locals = {
  className: '_23_aKvs-b8bW2Vg3fwHozO',
  subClass: '_13LGdX8RMStbBE9w-t0gZ1',
};

CamelCase is recommended for local selectors. They are easier to use within the imported JS module.

You can use :local(#someId), but this is not recommended. Use classes instead of ids.

`Composing`

When declaring a local classname you can compose a local class from another local classname.

:local(.className) {
  background: red;
  color: yellow;
}

:local(.subClass) {
  composes: className;
  background: blue;
}

This doesn't result in any change to the CSS itself but exports multiple classnames.

exports.locals = {
  className: '_23_aKvs-b8bW2Vg3fwHozO',
  subClass: '_13LGdX8RMStbBE9w-t0gZ1 _23_aKvs-b8bW2Vg3fwHozO',
};

._23_aKvs-b8bW2Vg3fwHozO {
  background: red;
  color: yellow;
}

._13LGdX8RMStbBE9w-t0gZ1 {
  background: blue;
}

`Importing`

To import a local classname from another module.

:local(.continueButton) {
  composes: button from 'library/button.css';
  background: red;
}

:local(.nameEdit) {
  composes: edit highlight from './edit.css';
  background: red;
}

To import from multiple modules use multiple composes: rules.

:local(.className) {
  composes: edit hightlight from './edit.css';
  composes: button from 'module/button.css';
  composes: classFromThisModule;
  background: red;
}

`localIdentName`

Type: String Default: [hash:base64]

You can configure the generated ident with the localIdentName query parameter. See loader-utils's documentation for more information on options.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          modules: true,
          localIdentName: '[path][name]__[local]--[hash:base64:5]',
        },
      },
    ],
  },
};

You can also specify the absolute path to your custom getLocalIdent function to generate classname based on a different schema.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          modules: true,
          context: path.resolve(__dirname, 'context'), // Allow to redefine basic loader context for `local-ident-name`
          hashPrefix: 'hash', // Allow to add custom hash to generate more unique classes
          localIdentName: '[path][name]__[local]--[hash:base64:5]',
          getLocalIdent: (context, localIdentName, localName, options) => {
            return 'whatever_random_class_name';
          },
        },
      },
    ],
  },
};

`sourceMap`

Type: Boolean Default: true

To include source maps set the sourceMap option.

I.e. the mini-css-extract-plugin can handle them.

They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS source maps do not). In addition to that relative paths are buggy and you need to use an absolute public path which includes the server URL.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          sourceMap: true,
        },
      },
    ],
  },
};

`camelCase`

Type: Boolean|String Default: false

By default, the exported JSON keys mirror the class names. If you want to camelize class names (useful in JS), pass the query parameter camelCase to css-loader.

Name	Type	Description
`false`	`{Boolean}`	Class names will be camelized, the original class name will not to be removed from the locals
`true`	`{Boolean}`	Class names will be camelized
`'dashes'`	`{String}`	Only dashes in class names will be camelized
`'only'`	`{String}`	Introduced in `0.27.1`. Class names will be camelized, the original class name will be removed from the locals
`'dashesOnly'`	`{String}`	Introduced in `0.27.1`. Dashes in class names will be camelized, the original class name will be removed from the locals

file.css

.class-name {
}

file.js

import { className } from 'file.css';

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          camelCase: true,
        },
      },
    ],
  },
};

`importLoaders`

Type: Number Default: 0

The option importLoaders allows you to configure how many loaders before css-loader should be applied to @imported resources.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: {
              importLoaders: 2, // 0 => no loaders (default); 1 => postcss-loader; 2 => postcss-loader, sass-loader
            },
          },
          'postcss-loader',
          'sass-loader',
        ],
      },
    ],
  },
};

This may change in the future when the module system (i. e. webpack) supports loader matching by origin.

`exportOnlyLocals`

Type: Boolean Default: false

Export only locals (useful when you use css modules). For pre-rendering with mini-css-extract-plugin you should use this option instead of style-loader!css-loader in the pre-rendering bundle. It doesn't embed CSS but only exports the identifier mappings.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        loader: 'css-loader',
        options: {
          exportOnlyLocals: true,
        },
      },
    ],
  },
};

Examples

Assets

The following webpack.config.js can load CSS files, embed small PNG/JPG/GIF/SVG images as well as fonts as Data URLs and copy larger files to the output directory.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ['style-loader', 'css-loader'],
      },
      {
        test: /\.(png|jpg|gif|svg|eot|ttf|woff|woff2)$/,
        loader: 'url-loader',
        options: {
          limit: 10000,
        },
      },
    ],
  },
};

Extract

For production builds it's recommended to extract the CSS from your bundle being able to use parallel loading of CSS/JS resources later on. This can be achieved by using the mini-css-extract-plugin to extract the CSS when running in production mode.

seuros/css-loader