css-loader

by webpack-contrib

webpack-contrib /css-loader

CSS Loader

3.8K Stars 551 Forks Last release: 14 days ago (v4.3.0) MIT License 595 Commits 84 Releases

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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}
|
true
| Enables/Disables
url
/
image-set
functions handling | |
import
|
{Boolean\|Function}
|
true
| Enables/Disables
@import
at-rules handling | |
modules
|
{Boolean\|String\|Object}
|
{auto: true}
| Enables/Disables CSS Modules and their configuration | |
sourceMap
|
{Boolean}
|
compiler.devtool
| Enables/Disables generation of source maps | |
importLoaders
|
{Number}
|
0
| Enables/Disables or setups number of loaders applied before CSS loader | |
esModule
|
{Boolean}
|
true
| Use ES modules syntax |

url

Type:

Boolean|Function
Default:
true

Enables/Disables

url
/
image-set
functions handling. 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$/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|Function
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: (url, media, resourcePath) => {
            // resourcePath - path to css file

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

        return true;
      },
    },
  },
],

}, };

modules

Type:

Boolean|String|Object
Default: based on filename,
true
for all files matching
/\.module\.\w+$/i.test(filename)
regular expression, more information you can read here

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. Using
pure
value requires selectors must contain at least one local class or id.

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.

i We strongly recommend that you specify the extension when importing a file, since it is possible to import a file with any extension and it is not known in advance which file to use.

: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: {
            compileType: 'module',
            mode: 'local',
            auto: true,
            exportGlobals: true,
            localIdentName: '[path][name]__[local]--[hash:base64:5]',
            context: path.resolve(__dirname, 'src'),
            localIdentHashPrefix: 'my-custom-hash',
            namedExport: true,
            exportLocalsConvention: 'camelCase',
            exportOnlyLocals: false,
          },
        },
      },
    ],
  },
};
compileType

Type:

'module' | 'icss'
Default:
'module'

Controls the level of compilation applied to the input styles.

The

module
handles
class
and
id
scoping and
@value
values. The
icss
will only compile the low level
Interoperable CSS
format for declaring
:import
and
:export
dependencies between CSS and other languages.

ICSS underpins CSS Module support, and provides a low level syntax for other tools to implement CSS-module variations of their own.

webpack.config.js

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

Type:

Boolean|RegExp|Function
Default:
'true'

Allows auto enable CSS modules based on filename.

Boolean

Possible values:

  • true
    - enable css modules for all files for which
    /\.module\.\w+$/i.test(filename)
    return true
  • false
    - disable css modules

webpack.config.js

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

Enable css modules for files based on the filename satisfying your regex check.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            auto: /\.custom-module\.\w+$/i,
          },
        },
      },
    ],
  },
};
Function

Enable css modules for files based on the filename satisfying your filter function check.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            auto: (resourcePath) => resourcePath.endsWith('.custom-module.css'),
          },
        },
      },
    ],
  },
};
mode

Type:

String|Function
Default:
'local'

Setup

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

Possible values -

local
,
global
, and
pure
.

webpack.config.js

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

Allows set different values for the

mode
option based on a filename

Possible return values -

local
,
global
, and
pure
.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: 'css-loader',
        options: {
          modules: {
            // Callback must return "local", "global", or "pure" values
            mode: (resourcePath) => {
              if (/pure.css$/i.test(resourcePath)) {
                return 'pure';
              }

          if (/global.css$/i.test(resourcePath)) {
            return 'global';
          }

          return 'local';
        },
      },
    },
  },
],

}, };

localIdentName

Type:

String
Default:
'[hash:base64]'

Allows to configure the generated local ident name. 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]',
          },
        },
      },
    ],
  },
};
localIdentContext

Type:

String
Default:
compiler.context

Allows to redefine basic loader context for local ident name.

webpack.config.js

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

Type:

String
Default:
undefined

Allows to add custom hash to generate more unique classes.

webpack.config.js

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

Type:

Function
Default:
undefined

Allows to specify a function to generate the classname. 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';
            },
          },
        },
      },
    ],
  },
};
namedExport

Type:

Boolean
Default:
false

Enables/disables ES modules named export for locals.

⚠ Names of locals are converted to camelcase, i.e. the

exportLocalsConvention
option has
camelCaseOnly
value by default.

⚠ It is not allowed to use JavaScript reserved words in css class names.

styles.css

.foo-baz {
  color: red;
}
.bar {
  color: blue;
}

index.js

import { fooBaz, bar } from './styles.css';

console.log(fooBaz, bar);

You can enable a ES module named export using:

webpack.config.js

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

Type:

Boolean
Default:
false

Allow

css-loader
to export names from global class or id, so you can use that as local name.

webpack.config.js

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

Type:

String
Default: based on the
modules.namedExport
option value, if
true
-
camelCaseOnly
, otherwise
asIs

Style of exported class names.

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

asIs
value).

⚠ Only

camelCaseOnly
value allowed if you set the
namedExport
value to
true
.

| Name | Type | Description | | :-------------------: | :--------: | :----------------------------------------------------------------------------------------------- | |

'asIs'
|

{String}
| Class names will be exported as is. | |
'camelCase'
|
{String}
| Class names will be camelized, the original class name will not to be removed from the locals | |
'camelCaseOnly'
|
{String}
| Class names will be camelized, the original class name will be removed from the locals | |
'dashes'
|
{String}
| Only dashes in class names will be camelized | |
'dashesOnly'
|
{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: {
          mode: 'local',
          localsConvention: 'camelCase',
        },
      },
    ],
  },
};
exportOnlyLocals

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: {
          modules: {
            exportOnlyLocals: true,
          },
        },
      },
    ],
  },
};

sourceMap

Type:

Boolean
Default: depends on the
compiler.devtool
value

By default generation of source maps depends on the

devtool
option. All values enable source map generation except

eval
and
false
value.

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
@import
ed 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.

esModule

Type:

Boolean
Default:
true

By default,

css-loader
generates JS modules that use the ES modules syntax. There are some cases in which using ES modules is beneficial, like in the case of module concatenation and tree shaking.

You can enable a CommonJS modules syntax using:

webpack.config.js

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

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

Pure CSS, CSS modules and PostCSS

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

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        // For pure CSS - /\.css$/i,
        // For Sass/SCSS - /\.((c|sa|sc)ss)$/i,
        // For Less - /\.((c|le)ss)$/i,
        test: /\.((c|sa|sc)ss)$/i,
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: {
              // Run `postcss-loader` on each CSS `@import`, do not forget that `sass-loader` compile non CSS `@import`'s into a single file
              // If you need run `sass-loader` and `postcss-loader` on each CSS `@import` please set it to `2`
              importLoaders: 1,
              // Automatically enable css modules for files satisfying `/\.module\.\w+$/i` RegExp.
              modules: { auto: true },
            },
          },
          {
            loader: 'postcss-loader',
            options: { plugins: () => [postcssPresetEnv({ stage: 0 })] },
          },
          // Can be `less-loader`
          {
            loader: 'sass-loader',
          },
        ],
      },
      {
        test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/i,
        loader: 'url-loader',
        options: {
          limit: 8192,
        },
      },
    ],
  },
};

Resolve unresolved URLs using an alias

index.css

.class {
  background: url(/assets/unresolved/img.png);
}

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: ['style-loader', 'css-loader'],
      },
    ],
  },
  resolve: {
    alias: {
      '/assets/unresolved/img.png': path.resolve(
        __dirname,
        'assets/real-path-to-img/img.png'
      ),
    },
  },
};

Separating
Interoperable CSS
-only and
CSS Module
features

The following setup is an example of allowing

Interoperable CSS
features only (such as
:import
and
:export
) without using further
CSS Module
functionality by setting
compileType
option for all files that do not match
*.module.scss
naming convention. This is for reference as having
ICSS
features applied to all files was default
css-loader
behavior before v4.
Meanwhile all files matching
*.module.scss
are treated as
CSS Modules
in this example.

An example case is assumed where a project requires canvas drawing variables to be synchronized with CSS - canvas drawing uses the same color (set by color name in JavaScript) as HTML background (set by class name in CSS).

webpack.config.js

module.exports = {
  module: {
    rules: [
      // ...
      // --------
      // SCSS ALL EXCEPT MODULES
      {
        test: /\.scss$/,
        exclude: /\.module\.scss$/,
        use: [
          {
            loader: 'style-loader'
          },
          {
            loader: 'css-loader',
            options: {
              importLoaders: 1,
              modules: {
                compileType: 'icss'
              }
            }
          },
          {
            loader: 'sass-loader'
          },
        ],
      },
      // --------
      // SCSS MODULES
      {
        test: /\.module\.scss$/,
        use: [
          {
            loader: 'style-loader'
          },
          {
            loader: 'css-loader',
            options: {
              importLoaders: 1,
              modules: {
                compileType: 'module'
              }
            }
          },
          {
            loader: 'sass-loader'
          },
        ],
      },
      // --------
      // ...
  },
};

variables.scss

File treated as

ICSS
-only.
$colorBackground: red;
:export {
  colorBackgroundCanvas: $colorBackground;
}

Component.module.scss

File treated as

CSS Module
.
@import 'variables.scss';
.componentClass {
  background-color: $colorBackground;
}

Component.jsx

Using both

CSS Module
functionality as well as SCSS variables directly in JavaScript.
import svars from 'variables.scss';
import styles from 'Component.module.scss';

// Render DOM with CSS modules class name //

// //

// Somewhere in JavaScript canvas drawing code use the variable directly // const ctx = mountsCanvas.current.getContext('2d',{alpha: false}); ctx.fillStyle = ${svars.colorBackgroundCanvas};

Contributing

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

CONTRIBUTING

License

MIT

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