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webpack-contrib
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Description

CSS Loader

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css-loader

The

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

Getting Started

⚠ To use css-loader, [email protected] is required

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"],
      },
    ],
  },
};

And run

webpack
via your preferred method.

If, for one reason or another, you need to extract CSS as a file (i.e. do not store CSS in a JS module) you might want to check out the recommend example.

Options

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

url
|

{Boolean\|Object}
|
true
| Allows to enables/disables
url()
/
image-set()
functions handling | |
import
|
{Boolean\|Object}
|
true
| Allows to enables/disables
@import
at-rules handling | |
modules
|
{Boolean\|String\|Object}
|
{auto: true}
| Allows to enables/disables or setup CSS Modules options | |
sourceMap
|
{Boolean}
|
compiler.devtool
| Enables/Disables generation of source maps | |
importLoaders
|
{Number}
|
0
| Allows enables/disables or setups number of loaders applied before CSS loader for
@import
/CSS Modules and ICSS imports | |
esModule
|
{Boolean}
|
true
| Use ES modules syntax | |
exportType
|
{'array' \| 'string' \| 'css-style-sheet'}
|
array
| Allows exporting styles as array with modules, string or constructable stylesheet (i.e.
CSSStyleSheet
) |

url

Type:

Boolean|Object
Default:
true

Allow to enable/disables handling the CSS functions

url
and
image-set
. If set to
false
,
css-loader
will not parse any paths specified in
url
or
image-set
. A function can also be passed to control this behavior dynamically based on the path to the asset. Starting with version 4.0.0, absolute paths are parsed based on the server root.

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,
        },
      },
    ],
  },
};

Object

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: {
            filter: (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|Object
Default:
true

Allows to 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,
        },
      },
    ],
  },
};

Object

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

filter
|

{Function}
|
undefined
| Allow to filter
@import
|
filter

Type:

Function
Default:
undefined

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: {
            filter: (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:
undefined

Allows to enable/disable CSS Modules or ICSS and setup configuration:

  • undefined
    - enable CSS modules for all files matching
    /\.module\.\w+$/i.test(filename)
    and
    /\.icss\.\w+$/i.test(filename)
    regexp.
  • true
    - enable CSS modules for all files.
  • false
    - disables CSS Modules for all files.
  • string
    - disables CSS Modules for all files and set the
    mode
    option, more information you can read here
  • object
    - enable CSS modules for all files, if
    modules.auto
    option is not specified, otherwise the
    modules.auto
    option will determine whether if it is CSS modules or not, more information you can read here

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

Type:

Boolean|RegExp|Function
Default:
undefined

Allows auto enable CSS modules/ICSS based on filename when

modules
option is object.

Possible values:

  • undefined
    - enable CSS modules for all files.
  • true
    - enable CSS modules for all files matching
    /\.module\.\w+$/i.test(filename)
    and
    /\.icss\.\w+$/i.test(filename)
    regexp.
  • false
    - disables CSS Modules.
  • RegExp
    - enable CSS modules for all files matching
    /RegExp/i.test(filename)
    regexp.
  • function
    - enable CSS Modules for files based on the filename satisfying your filter function check.
Boolean

Possible values:

  • true
    - enables CSS modules or interoperable CSS format, sets the
    modules.mode
    option to
    local
    value for all files which satisfy
    /\.module(s)?\.\w+$/i.test(filename)
    condition or sets the
    modules.mode
    option to
    icss
    value for all files which satisfy
    /\.icss\.\w+$/i.test(filename)
    condition
  • false
    - disables CSS modules or interoperable CSS format based on filename

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.

Controls the level of compilation applied to the input styles.

The

local
,
global
, and
pure
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.

String

Possible values -

local
,
global
,
pure
, and
icss
.

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
,
pure
and
icss
.

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.

For more information on options see:

Supported template strings:

  • [name]
    the basename of the resource
  • [folder]
    the folder the resource relative to the
    compiler.context
    option or
    modules.localIdentContext
    option.
  • [path]
    the path of the resource relative to the
    compiler.context
    option or
    modules.localIdentContext
    option.
  • [file]
    - filename and path.
  • [ext]
    - extension with leading
    .
    .
  • [hash]
    - the hash of the string, generated based on
    localIdentHashSalt
    ,
    localIdentHashFunction
    ,
    localIdentHashDigest
    ,
    localIdentHashDigestLength
    ,
    localIdentContext
    ,
    resourcePath
    and
    exportName
  • [:hash::]
    - hash with hash settings.
  • [local]
    - original class.

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: {
            localIdentContext: path.resolve(__dirname, "src"),
          },
        },
      },
    ],
  },
};
localIdentHashSalt

Type:

String
Default:
undefined

Allows to add custom hash to generate more unique classes. For more information see output.hashSalt.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            localIdentHashSalt: "hash",
          },
        },
      },
    ],
  },
};
localIdentHashFunction

Type:

String
Default:
md4

Allows to specify hash function to generate classes . For more information see output.hashFunction.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            localIdentHashFunction: "md4",
          },
        },
      },
    ],
  },
};
localIdentHashDigest

Type:

String
Default:
hex

Allows to specify hash digest to generate classes. For more information see output.hashDigest.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            localIdentHashDigest: "base64",
          },
        },
      },
    ],
  },
};
localIdentHashDigestLength

Type:

Number
Default:
20

Allows to specify hash digest length to generate classes. For more information see output.hashDigestLength.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            localIdentHashDigestLength: 5,
          },
        },
      },
    ],
  },
};
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. If the custom function returns

null
or
undefined
, we fallback to the built-in function to generate the 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,
          },
        },
      },
    ],
  },
};

To set a custom name for namedExport, can use

exportLocalsConvention
option as a function. Example below in the
examples
section.

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

Style of exported class names.

String

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: {
          modules: {
            exportLocalsConvention: "camelCase",
          },
        },
      },
    ],
  },
};
Function

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            exportLocalsConvention: function (name) {
              return name.replace(/-/g, "_");
            },
          },
        },
      },
    ],
  },
};

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            exportLocalsConvention: function (name) {
              return [
                name.replace(/-/g, "_"),
                // dashesCamelCase
                name.replace(/-+(\w)/g, (match, firstLetter) =>
                  firstLetter.toUpperCase()
                ),
              ];
            },
          },
        },
      },
    ],
  },
};
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,
          },
        },
      },
    ],
  },
};

importLoaders

Type:

Number
Default:
0

Allows to enables/disables or setups number of loaders applied before CSS loader for

@import
at-rules, CSS modules and ICSS imports, i.e.
@import
/
composes
/
@value value from './values.css'
/etc.

The option

importLoaders
allows you to configure how many loaders before
css-loader
should be applied to
@import
ed resources and CSS modules/ICSS imports.

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.

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,
        },
      },
    ],
  },
};

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,
        },
      },
    ],
  },
};

exportType

Type:

'array' | 'string' | 'css-style-sheet'
Default:
'array'

Allows exporting styles as array with modules, string or constructable stylesheet (i.e.

CSSStyleSheet
). Default value is

'array'
, i.e. loader exports array of modules with specific API which is used in
style-loader
or other.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        assert: { type: "css" },
        loader: "css-loader",
        options: {
          exportType: "css-style-sheet",
        },
      },
    ],
  },
};

src/index.js

import sheet from "./styles.css" assert { type: "css" };

document.adoptedStyleSheets = [sheet]; shadowRoot.adoptedStyleSheets = [sheet];

'array'

The default export is array of modules with specific API which is used in

style-loader
or other.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.(sa|sc|c)ss$/i,
        use: ["style-loader", "css-loader", "postcss-loader", "sass-loader"],
      },
    ],
  },
};

src/index.js

// `style-loader` applies styles to DOM
import "./styles.css";

'string'

⚠ You don't need

style-loader
anymore, please remove it. ⚠ The

esModules
option should be enabled if you want to use it with
CSS modules
, by default for locals will be used named export.

The default export is

string
.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.(sa|sc|c)ss$/i,
        use: ["css-loader", "postcss-loader", "sass-loader"],
      },
    ],
  },
};

src/index.js

import sheet from "./styles.css";

console.log(sheet);

'css-style-sheet'

@import
rules not yet allowed, more information ⚠ You don't need
style-loader
anymore, please remove it. ⚠ The
esModules
option should be enabled if you want to use it with
CSS modules
, by default for locals will be used named export. ⚠ Source maps are not currently supported in
Chrome
due bug

The default export is a constructable stylesheet (i.e.

CSSStyleSheet
).

Useful for custom elements and shadow DOM.

More information:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        assert: { type: "css" },
        loader: "css-loader",
        options: {
          exportType: "css-style-sheet",
        },
      },

  // For Sass/SCSS:
  //
  // {
  //   assert: { type: "css" },
  //   rules: [
  //     {
  //       loader: "css-loader",
  //       options: {
  //         exportType: "css-style-sheet",
  //         // Other options
  //       },
  //     },
  //     {
  //       loader: "sass-loader",
  //       options: {
  //         // Other options
  //       },
  //     },
  //   ],
  // },
],

}, };

src/index.js

// Example for Sass/SCSS:
// import sheet from "./styles.scss" assert { type: "css" };

// Example for CSS modules: // import sheet, { myClass } from "./styles.scss" assert { type: "css" };

// Example for CSS: import sheet from "./styles.css" assert { type: "css" };

document.adoptedStyleSheets = [sheet]; shadowRoot.adoptedStyleSheets = [sheet];

For migration purposes, you can use the following configuration:

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        oneOf: [
          {
            assert: { type: "css" },
            loader: "css-loader",
            options: {
              exportType: "css-style-sheet",
              // Other options
            },
          },
          {
            use: [
              "style-loader",
              {
                loader: "css-loader",
                options: {
                  // Other options
                },
              },
            ],
          },
        ],
      },
    ],
  },
};

Examples

Recommend

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, because it creates separate css files. For
development
mode (including
webpack-dev-server
) you can use style-loader, because it injects CSS into the DOM using multiple and works faster.

i Do not use together

style-loader
and
mini-css-extract-plugin
.

webpack.config.js

const MiniCssExtractPlugin = require("mini-css-extract-plugin");
const devMode = process.env.NODE_ENV !== "production";

module.exports = { module: { rules: [ { test: /.(sa|sc|c)ss$/i, use: [ devMode ? "style-loader" : MiniCssExtractPlugin.loader, "css-loader", "postcss-loader", "sass-loader", ], }, ], }, plugins: [].concat(devMode ? [] : [new MiniCssExtractPlugin()]), };

Disable url resolving using the
/* webpackIgnore: true */
comment

With the help of the

/* webpackIgnore: true */
comment, it is possible to disable sources handling for rules and for individual declarations.
/* webpackIgnore: true */
@import url(./basic.css);
@import /* webpackIgnore: true */ url(./imported.css);

.class { /* Disabled url handling for the all urls in the 'background' declaration / color: red; / webpackIgnore: true */ background: url("./url/img.png"), url("./url/img.png"); }

.class { /* Disabled url handling for the first url in the 'background' declaration / color: red; background: / webpackIgnore: true */ url("./url/img.png"), url("./url/img.png"); }

.class { /* Disabled url handling for the second url in the 'background' declaration / color: red; background: url("./url/img.png"), / webpackIgnore: true */ url("./url/img.png"); }

/* prettier-ignore / .class { / Disabled url handling for the second url in the 'background' declaration / color: red; background: url("./url/img.png"), / webpackIgnore: true */ url("./url/img.png"); }

/* prettier-ignore / .class { / Disabled url handling for third and sixth urls in the 'background-image' declaration / background-image: image-set( url(./url/img.png) 2x, url(./url/img.png) 3x, / webpackIgnore: true / url(./url/img.png) 4x, url(./url/img.png) 5x, url(./url/img.png) 6x, / webpackIgnore: true */ url(./url/img.png) 7x ); }

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.

For webpack v5:

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,
        // More information here https://webpack.js.org/guides/asset-modules/
        type: "asset",
      },
    ],
  },
};

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` and CSS modules/ICSS imports, 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,
            },
          },
          {
            loader: "postcss-loader",
            options: { plugins: () => [postcssPresetEnv({ stage: 0 })] },
          },
          // Can be `less-loader`
          {
            loader: "sass-loader",
          },
        ],
      },
      // For webpack v5
      {
        test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/i,
        // More information here https://webpack.js.org/guides/asset-modules/
        type: "asset",
      },
    ],
  },
};

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"
      ),
    },
  },
};

Named export with custom export names

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            namedExport: true,
            exportLocalsConvention: function (name) {
              return name.replace(/-/g, "_");
            },
          },
        },
      },
    ],
  },
};

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
mode
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$/i,
        exclude: /\.module\.scss$/i,
        use: [
          {
            loader: "style-loader",
          },
          {
            loader: "css-loader",
            options: {
              importLoaders: 1,
              modules: {
                mode: "icss",
              },
            },
          },
          {
            loader: "sass-loader",
          },
        ],
      },
      // --------
      // SCSS MODULES
      {
        test: /\.module\.scss$/i,
        use: [
          {
            loader: "style-loader",
          },
          {
            loader: "css-loader",
            options: {
              importLoaders: 1,
              modules: {
                mode: "local",
              },
            },
          },
          {
            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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