W3cubDocs

/webpack 4

css-loader

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

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$/i,
        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$/i,
        use: ['to-string-loader', 'css-loader'],
      },
    ],
  },
};

or

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$/i,
        use: [
          'handlebars-loader', // handlebars loader expects raw resource string
          'extract-loader',
          'css-loader',
        ],
      },
    ],
  },
};

Options

Name Type Default Description

url

{Boolean\|Function}

 {Boolean\|Function} true Enables/Disables url / image-set functions handling

import

{Boolean\|Function}

 {Boolean\|Function} true Enables/Disables @import at-rules handling

modules

{Boolean\|String\|Object}

 {Boolean\|String\|Object} false Enables/Disables CSS Modules and their configuration

sourceMap

{Boolean}

 {Boolean} false Enables/Disables generation of source maps

importLoaders

{Number}

 {Number} 0 Enables/Disables or setups number of loaders applied before CSS loader

localsConvention

{String}

 {String} asIs Style of exported classnames

onlyLocals

{Boolean}

 {Boolean} false Export only locals

url

Type: Boolean|Function Default: true

Enables/Disables url/image-set functions handling. Control url() resolving. Absolute URLs and root-relative 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$/i,
        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$/i,
        loader: 'css-loader',
        options: {
          url: (url, resourcePath) => {
            // resourcePath - path to css file

            // Don't handle `img.png` urls
            if (url.includes('img.png')) {
              return false;
            }

            return true;
          },
        },
      },
    ],
  },
};

import

Type: Boolean Default: true

Enables/Disables @import at-rules handling. 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$/i,
        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$/i,
        loader: 'css-loader',
        options: {
          import: (parsedImport, resourcePath) => {
            // parsedImport.url - url of `@import`
            // parsedImport.media - media query of `@import`
            // resourcePath - path to css file

            // Don't handle `style.css` import
            if (parsedImport.url.includes('style.css')) {
              return false;
            }

            return true;
          },
        },
      },
    ],
  },
};

modules

Type: Boolean|String|Object Default: false

Enables/Disables CSS Modules and their configuration.

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

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.

webpack.config.js

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

Features

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) notation 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;
}
Values

You can use @value to specific values to be reused throughout a document.

We recommend use prefix v- for values, s- for selectors and m- for media at-rules.

@value v-primary: #BF4040;
@value s-black: black-selector;
@value m-large: (min-width: 960px);

.header {
  color: v-primary;
  padding: 0 10px;
}

.s-black {
  color: black;
}

@media m-large {
  .header {
    padding: 0 20px;
  }
}

Boolean

Enable CSS Modules features.

webpack.config.js

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

String

Enable CSS Modules features and setup mode.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          // Using `local` value has same effect like using `modules: true`
          modules: 'global',
        },
      },
    ],
  },
};

Object

Enable CSS Modules features and setup options for them.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            mode: 'local',
            localIdentName: '[path][name]__[local]--[hash:base64:5]',
            context: path.resolve(__dirname, 'src'),
            hashPrefix: 'my-custom-hash',
          },
        },
      },
    ],
  },
};
mode

Type: String Default: local

Setup mode option. You can omit the value when you want local mode.

webpack.config.js

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

Recommendations:

  • use [path][name]__[local] for development
  • use [hash:base64] for production

The [local] placeholder contains original class.

Note: all reserved (<>:"/\|?*) and control filesystem characters (excluding characters in the [local] placeholder) will be converted to -.

webpack.config.js

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

Type: String Default: undefined

Allow to redefine basic loader context for local ident name. By default we use rootContext of loader.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            context: path.resolve(__dirname, 'context'),
          },
        },
      },
    ],
  },
};
hashPrefix

Type: String Default: undefined

Allow to add custom hash to generate more unique classes.

webpack.config.js

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

Type: Function Default: undefined

You can also specify the absolute path to your custom getLocalIdent function to generate classname based on a different schema. By default we use built-in function to generate a classname.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            getLocalIdent: (context, localIdentName, localName, options) => {
              return 'whatever_random_class_name';
            },
          },
        },
      },
    ],
  },
};
localIdentRegExp

Type: String|RegExp Default: undefined

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            localIdentRegExp: /page-(.*)\.css/i,
          },
        },
      },
    ],
  },
};

sourceMap

Type: Boolean Default: false

Enables/Disables generation of source maps.

To include source maps set the sourceMap option.

They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS source maps do not).

webpack.config.js

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

importLoaders

Type: Number Default: 0

Enables/Disables or setups number of loaders applied before CSS loader.

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$/i,
        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.

localsConvention

Type: String Default: undefined

Style of exported classnames.

By default, the exported JSON keys mirror the class names (i.e asIs value).

Name Type Description

'asIs'

{String}

 {String} Class names will be exported as is.

'camelCase'

{String}

 {String} Class names will be camelized, the original class name will not to be removed from the locals

'camelCaseOnly'

{String}

 {String} Class names will be camelized, the original class name will be removed from the locals

'dashes'

{String}

 {String} Only dashes in class names will be camelized

'dashesOnly'

{String}

 {String} 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$/i,
        loader: 'css-loader',
        options: {
          localsConvention: 'camelCase',
        },
      },
    ],
  },
};

onlyLocals

Type: Boolean Default: false

Export only locals.

Useful when you use css modules for pre-rendering (for example SSR). 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$/i,
        loader: 'css-loader',
        options: {
          onlyLocals: 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$/i,
        use: ['style-loader', 'css-loader'],
      },
      {
        test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/i,
        loader: 'url-loader',
        options: {
          limit: 8192,
        },
      },
    ],
  },
};

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.

  • As an alternative, if seeking better development performance and css outputs that mimic production. extract-css-chunks-webpack-plugin offers a hot module reload friendly, extended version of mini-css-extract-plugin. HMR real CSS files in dev, works like mini-css in non-dev

CSS modules and pure CSS

When you have pure CSS (without CSS modules) and CSS modules in project you can use this setup:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        // For pure CSS (without CSS modules)
        test: /\.css$/i,
        exclude: /\.module\.css$/i,
        use: ['style-loader', 'css-loader'],
      },
      {
        // For CSS modules
        test: /\.module\.css$/i,
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: {
              modules: true,
            },
          },
        ],
      },
      {
        test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/i,
        loader: 'url-loader',
        options: {
          limit: 8192,
        },
      },
    ],
  },
};

Contributing

Please take a moment to read our contributing guidelines if you haven't yet done so.

CONTRIBUTING

License

MIT

© JS Foundation and other contributors
Licensed under the Creative Commons Attribution License 4.0.
https://v4.webpack.js.org/loaders/css-loader