source: frontend/node_modules/css-loader/README.md

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# css-loader

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

## Getting Started

> **Warning**
>
> To use the latest version of css-loader, webpack@5 is required

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

```console
npm install --save-dev css-loader
```

or

```console
yarn add -D css-loader
```

or

```console
pnpm add -D css-loader
```

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

**file.js**

```js
import css from "file.css";
```

**webpack.config.js**

```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](https://github.com/webpack-contrib/css-loader#recommend).

## Options

- **[`url`](#url)**
- **[`import`](#import)**
- **[`modules`](#modules)**
- **[`sourceMap`](#sourcemap)**
- **[`importLoaders`](#importloaders)**
- **[`esModule`](#esmodule)**
- **[`exportType`](#exporttype)**

### `url`

Type:

```ts
type url =
  | boolean
  | {
      filter: (url: string, resourcePath: string) => boolean;
    };
```

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](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md#400-2020-07-25), absolute paths are parsed based on the server root.

Examples resolutions:

```js
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 `~`:

```js
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**

```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**

```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;
              }

              // Don't handle images under root-relative /external_images/
              if (/^\/external_images\//.test(path)) {
                return false;
              }

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

### `import`

Type:

<!-- use other name to prettify since import is reserved keyword -->

```ts
type importFn =
  | boolean
  | {
      filter: (
        url: string,
        media: string,
        resourcePath: string,
        supports?: string,
        layer?: string
      ) => boolean;
    };
```

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**

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

#### `object`

##### `filter`

Type:

```ts
type filter = (url: string, media: string, resourcePath: string) => boolean;
```

Default: `undefined`

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

**webpack.config.js**

```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:

```ts
type modules =
  | boolean
  | "local"
  | "global"
  | "pure"
  | "icss"
  | {
      auto: boolean | regExp | ((resourcePath: string) => boolean);
      mode:
        | "local"
        | "global"
        | "pure"
        | "icss"
        | ((resourcePath) => "local" | "global" | "pure" | "icss");
      localIdentName: string;
      localIdentContext: string;
      localIdentHashSalt: string;
      localIdentHashFunction: string;
      localIdentHashDigest: string;
      localIdentRegExp: string | regExp;
      getLocalIdent: (
        context: LoaderContext,
        localIdentName: string,
        localName: string
      ) => string;
      namedExport: boolean;
      exportGlobals: boolean;
      exportLocalsConvention:
        | "asIs"
        | "camelCase"
        | "camelCaseOnly"
        | "dashes"
        | "dashesOnly"
        | ((name: string) => string);
      exportOnlyLocals: boolean;
    };
```

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](https://github.com/webpack-contrib/css-loader#mode)
- `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](https://github.com/webpack-contrib/css-loader#auto)

The `modules` option enables/disables the **[CSS Modules](https://github.com/css-modules/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**

```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](https://github.com/css-modules/css-modules).

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.

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

```css
._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;
}
```

> **Note**
>
> Identifiers are exported

```js
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.

```css
: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.

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

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

._13LGdX8RMStbBE9w-t0gZ1 {
  background: blue;
}
```

##### `Importing`

To import a local classname from another module.

> **Note**
>
> 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.

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

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

To import from multiple modules use multiple `composes:` rules.

```css
:local(.className) {
  composes: edit highlight from "./edit.css", button from "module/button.css", classFromThisModule;
  background: red;
}
```

or

```css
:local(.className) {
  composes: edit highlight 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.

```css
@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**

```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**

```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**

```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:

```ts
type auto =
  | boolean
  | regExp
  | ((
      resourcePath: string,
      resourceQuery: string,
      resourceFragment: string
    ) => boolean);
```

Default: `undefined`

Allows auto enable CSS modules/ICSS based on the filename, query or fragment 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`](#mode) option to `local` value for all files which satisfy `/\.module(s)?\.\w+$/i.test(filename)` condition or sets the [`modules.mode`](#mode) option to `icss` value for all files which satisfy `/\.icss\.\w+$/i.test(filename)` condition
- `false` - disables CSS modules or interoperable CSS format based on filename

**webpack.config.js**

```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**

```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, query or fragment satisfying your filter function check.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            auto: (resourcePath, resourceQuery, resourceFragment) => {
              return resourcePath.endsWith(".custom-module.css");
            },
          },
        },
      },
    ],
  },
};
```

##### `mode`

Type:

```ts
type mode =
  | "local"
  | "global"
  | "pure"
  | "icss"
  | ((
      resourcePath: string,
      resourceQuery: string,
      resourceFragment: string
    ) => "local" | "global" | "pure" | "icss");
```

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**

```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 the filename, query or fragment.

Possible return values - `local`, `global`, `pure` and `icss`.

**webpack.config.js**

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

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

              return "local";
            },
          },
        },
      },
    ],
  },
};
```

##### `localIdentName`

Type:

```ts
type localIdentName = string;
```

Default: `'[hash:base64]'`

Allows to configure the generated local ident name.

For more information on options see:

- [webpack template strings](https://webpack.js.org/configuration/output/#template-strings),
- [output.hashDigest](https://webpack.js.org/configuration/output/#outputhashdigest),
- [output.hashDigestLength](https://webpack.js.org/configuration/output/#outputhashdigestlength),
- [output.hashFunction](https://webpack.js.org/configuration/output/#outputhashfunction),
- [output.hashSalt](https://webpack.js.org/configuration/output/#outputhashsalt).

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`
- `[<hashFunction>:hash:<hashDigest>:<hashDigestLength>]` - 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**

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

##### `localIdentContext`

Type:

```ts
type localIdentContex = string;
```

Default: `compiler.context`

Allows to redefine basic loader context for local ident name.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            localIdentContext: path.resolve(__dirname, "src"),
          },
        },
      },
    ],
  },
};
```

##### `localIdentHashSalt`

Type:

```ts
type localIdentHashSalt = string;
```

Default: `undefined`

Allows to add custom hash to generate more unique classes.
For more information see [output.hashSalt](https://webpack.js.org/configuration/output/#outputhashsalt).

**webpack.config.js**

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

##### `localIdentHashFunction`

Type:

```ts
type localIdentHashFunction = string;
```

Default: `md4`

Allows to specify hash function to generate classes .
For more information see [output.hashFunction](https://webpack.js.org/configuration/output/#outputhashfunction).

**webpack.config.js**

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

##### `localIdentHashDigest`

Type:

```ts
type localIdentHashDigest = string;
```

Default: `hex`

Allows to specify hash digest to generate classes.
For more information see [output.hashDigest](https://webpack.js.org/configuration/output/#outputhashdigest).

**webpack.config.js**

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

##### `localIdentHashDigestLength`

Type:

```ts
type localIdentHashDigestLength = number;
```

Default: `20`

Allows to specify hash digest length to generate classes.
For more information see [output.hashDigestLength](https://webpack.js.org/configuration/output/#outputhashdigestlength).

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            localIdentHashDigestLength: 5,
          },
        },
      },
    ],
  },
};
```

##### `hashStrategy`

Type: `'resource-path-and-local-name' | 'minimal-subset'`
Default: `'resource-path-and-local-name'`

Should local name be used when computing the hash.

- `'resource-path-and-local-name'` Both resource path and local name are used when hashing. Each identifier in a module gets its own hash digest, always.
- `'minimal-subset'` Auto detect if identifier names can be omitted from hashing. Use this value to optimize the output for better GZIP or Brotli compression.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            hashStrategy: "minimal-subset",
          },
        },
      },
    ],
  },
};
```

##### `localIdentRegExp`

Type:

```ts
type localIdentRegExp = string | RegExp;
```

Default: `undefined`

**webpack.config.js**

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

##### `getLocalIdent`

Type:

```ts
type getLocalIdent = (
  context: LoaderContext,
  localIdentName: string,
  localName: string
) => string;
```

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**

```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:

```ts
type namedExport = boolean;
```

Default: `false`

Enables/disables ES modules named export for locals.

> **Warning**
>
> Names of locals are converted to camelcase, i.e. the `exportLocalsConvention` option has
> `camelCaseOnly` value by default. You can set this back to any other valid option but selectors
> which are not valid JavaScript identifiers may run into problems which do not implement the entire
> modules specification.

> **Warning**
>
> It is not allowed to use JavaScript reserved words in css class names unless
> `exportLocalsConvention` is `"asIs"`.

**styles.css**

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

**index.js**

```js
import * as styles from "./styles.css";

console.log(styles.fooBaz, styles.bar);
// or if using `exportLocalsConvention: "asIs"`:
console.log(styles["foo-baz"], styles.bar);
```

You can enable a ES module named export using:

**webpack.config.js**

```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`](#exportLocalsConvention) option as a function.
Example below in the [`examples`](#examples) section.

##### `exportGlobals`

Type:

```ts
type exportsGLobals = 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**

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

##### `exportLocalsConvention`

Type:

```ts
type exportLocalsConvention =
  | "asIs"
  | "camelCase"
  | "camelCaseOnly"
  | "dashes"
  | "dashesOnly"
  | ((name: string) => string);
```

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).

|         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**

```css
.class-name {
}
```

**file.js**

```js
import { className } from "file.css";
```

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        loader: "css-loader",
        options: {
          modules: {
            exportLocalsConvention: "camelCase",
          },
        },
      },
    ],
  },
};
```

###### `function`

**webpack.config.js**

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

**webpack.config.js**

```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:

```ts
type exportOnlyLocals = 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**

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

### `importLoaders`

Type:

```ts
type importLoaders = 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**

```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:

```ts
type sourceMap = boolean;
```

Default: depends on the `compiler.devtool` value

By default generation of source maps depends on the [`devtool`](https://webpack.js.org/configuration/devtool/) option. All values enable source map generation except `eval` and `false` value.

**webpack.config.js**

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

### `esModule`

Type:

```ts
type esModule = 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](https://webpack.js.org/plugins/module-concatenation-plugin/) and [tree shaking](https://webpack.js.org/guides/tree-shaking/).

You can enable a CommonJS modules syntax using:

**webpack.config.js**

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

### `exportType`

Type:

```ts
type exportType = "array" | "string" | "css-style-sheet";
```

Default: `'array'`

Allows exporting styles as array with modules, string or [constructable stylesheet](https://developers.google.com/web/updates/2019/02/constructable-stylesheets) (i.e. [`CSSStyleSheet`](https://developer.mozilla.org/en-US/docs/Web/API/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**

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

**src/index.js**

```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**

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

**src/index.js**

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

#### `'string'`

> **Warning**
>
> You should not use [`style-loader`](https://github.com/webpack-contrib/style-loader) or [`mini-css-extract-plugin`](https://github.com/webpack-contrib/mini-css-extract-plugin) with this value.

> **Warning**
>
> The `esModule` option should be enabled if you want to use it with [`CSS modules`](https://github.com/webpack-contrib/css-loader#modules), by default for locals will be used [named export](https://github.com/webpack-contrib/css-loader#namedexport).

The default export is `string`.

**webpack.config.js**

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

**src/index.js**

```js
import sheet from "./styles.css";

console.log(sheet);
```

#### `'css-style-sheet'`

> **Warning**
>
> `@import` rules not yet allowed, more [information](https://web.dev/css-module-scripts/#@import-rules-not-yet-allowed)

> **Warning**
>
> You don't need [`style-loader`](https://github.com/webpack-contrib/style-loader) anymore, please remove it.

> **Warning**
>
> The `esModule` option should be enabled if you want to use it with [`CSS modules`](https://github.com/webpack-contrib/css-loader#modules), by default for locals will be used [named export](https://github.com/webpack-contrib/css-loader#namedexport).

> **Warning**
>
> Source maps are not currently supported in `Chrome` due [bug](https://bugs.chromium.org/p/chromium/issues/detail?id=1174094&q=CSSStyleSheet%20source%20maps&can=2)

The default export is a [constructable stylesheet](https://developers.google.com/web/updates/2019/02/constructable-stylesheets) (i.e. [`CSSStyleSheet`](https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleSheet)).

Useful for [custom elements](https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_custom_elements) and shadow DOM.

More information:

- [Using CSS Module Scripts to import stylesheets](https://web.dev/css-module-scripts/)
- [Constructable Stylesheets: seamless reusable styles](https://developers.google.com/web/updates/2019/02/constructable-stylesheets)

**webpack.config.js**

```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**

```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:

```js
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](https://github.com/webpack-contrib/mini-css-extract-plugin), because it creates separate css files.
For `development` mode (including `webpack-dev-server`) you can use [style-loader](https://github.com/webpack-contrib/style-loader), because it injects CSS into the DOM using multiple `<style></style>` and works faster.

> **Note**
>
> Do not use `style-loader` and `mini-css-extract-plugin` together.

**webpack.config.js**

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

module.exports = {
  module: {
    rules: [
      {
        // If you enable `experiments.css` or `experiments.futureDefaults`, please uncomment line below
        // type: "javascript/auto",
        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.

```css
/* 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](https://tools.ietf.org/html/rfc2397) and copy larger files to the output directory.

**For webpack v5:**

**webpack.config.js**

```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](https://github.com/webpack-contrib/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](https://github.com/faceyspacey/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**

```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**

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

**webpack.config.js**

```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**

```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**

```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.

```scss
$colorBackground: red;
:export {
  colorBackgroundCanvas: $colorBackground;
}
```

**Component.module.scss**

File treated as `CSS Module`.

```scss
@import "variables.scss";
.componentClass {
  background-color: $colorBackground;
}
```

**Component.jsx**

Using both `CSS Module` functionality as well as SCSS variables directly in JavaScript.

```jsx
import svars from "variables.scss";
import styles from "Component.module.scss";

// Render DOM with CSS modules class name
// <div className={styles.componentClass}>
//   <canvas ref={mountsCanvas}/>
// </div>

// 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](./.github/CONTRIBUTING.md)

## License

[MIT](./LICENSE)

[npm]: https://img.shields.io/npm/v/css-loader.svg
[npm-url]: https://npmjs.com/package/css-loader
[node]: https://img.shields.io/node/v/css-loader.svg
[node-url]: https://nodejs.org
[tests]: https://github.com/webpack-contrib/css-loader/workflows/css-loader/badge.svg
[tests-url]: https://github.com/webpack-contrib/css-loader/actions
[cover]: https://codecov.io/gh/webpack-contrib/css-loader/branch/master/graph/badge.svg
[cover-url]: https://codecov.io/gh/webpack-contrib/css-loader
[discussion]: https://img.shields.io/github/discussions/webpack/webpack
[discussion-url]: https://github.com/webpack/webpack/discussions
[size]: https://packagephobia.now.sh/badge?p=css-loader
[size-url]: https://packagephobia.now.sh/result?p=css-loader