sass-loader/README.md

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# sass-loader

Loads a Sass/SCSS file and compiles it to CSS.

## Getting Started

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

```console
npm install sass-loader sass webpack --save-dev
```

or

```console
yarn add -D sass-loader sass webpack
```

or

```console
pnpm add -D sass-loader sass webpack
```

`sass-loader` requires you to install either [Dart Sass](https://github.com/sass/dart-sass), [Node Sass](https://github.com/sass/node-sass) on your own (more documentation can be found below) or [Sass Embedded](https://github.com/sass/embedded-host-node).

This allows you to control the versions of all your dependencies, and to choose which Sass implementation to use.

> **Note**
>
> We highly recommend using [Dart Sass](https://github.com/sass/dart-sass).

> **Warning**
>
> [Node Sass](https://github.com/sass/node-sass) does not work with [Yarn PnP](https://classic.yarnpkg.com/en/docs/pnp/) feature and doesn't support [@use rule](https://sass-lang.com/documentation/at-rules/use).

> **Warning**
>
> [Sass Embedded](https://github.com/sass/embedded-host-node) is experimental and in `beta`, therefore some features may not work

Chain the `sass-loader` with the [css-loader](https://github.com/webpack-contrib/css-loader) and the [style-loader](https://github.com/webpack-contrib/style-loader) to immediately apply all styles to the DOM or the [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) to extract it into a separate file.

Then add the loader to your Webpack configuration. For example:

**app.js**

```js
import "./style.scss";
```

**style.scss**

```scss
$body-color: red;

body {
  color: $body-color;
}
```

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          // Creates `style` nodes from JS strings
          "style-loader",
          // Translates CSS into CommonJS
          "css-loader",
          // Compiles Sass to CSS
          "sass-loader",
        ],
      },
    ],
  },
};
```

Finally run `webpack` via your preferred method.

### Resolving `import` at-rules

Webpack provides an [advanced mechanism to resolve files](https://webpack.js.org/concepts/module-resolution/).

The `sass-loader` uses Sass's custom importer feature to pass all queries to the Webpack resolving engine.
Thus you can import your Sass modules from `node_modules`.

```scss
@import "bootstrap";
```

Using `~` is deprecated and can be removed from your code (**we recommend it**), but we still support it for historical reasons.
Why can you remove it? The loader will first try to resolve `@import` as a relative path. If it cannot be resolved, then the loader will try to resolve `@import` inside [`node_modules`](https://webpack.js.org/configuration/resolve/#resolvemodules).

Prepending module paths with a `~` tells webpack to search through [`node_modules`](https://webpack.js.org/configuration/resolve/#resolvemodules).

```scss
@import "~bootstrap";
```

It's important to prepend it with only `~`, because `~/` resolves to the home directory.
Webpack needs to distinguish between `bootstrap` and `~bootstrap` because CSS and Sass files have no special syntax for importing relative files.
Writing `@import "style.scss"` is the same as `@import "./style.scss";`

### Problems with `url(...)`

Since Sass implementations don't provide [url rewriting](https://github.com/sass/libsass/issues/532), all linked assets must be relative to the output.

- If you pass the generated CSS on to the `css-loader`, all urls must be relative to the entry-file (e.g. `main.scss`).
- If you're just generating CSS without passing it to the `css-loader`, it must be relative to your web root.

You will be disrupted by this first issue. It is natural to expect relative references to be resolved against the `.sass`/`.scss` file in which they are specified (like in regular `.css` files).

Thankfully there are a two solutions to this problem:

- Add the missing url rewriting using the [resolve-url-loader](https://github.com/bholloway/resolve-url-loader). Place it before `sass-loader` in the loader chain.
- Library authors usually provide a variable to modify the asset path. [bootstrap-sass](https://github.com/twbs/bootstrap-sass) for example has an `$icon-font-path`.

## Options

- **[`implementation`](#implementation)**
- **[`sassOptions`](#sassoptions)**
- **[`sourceMap`](#sourcemap)**
- **[`additionalData`](#additionaldata)**
- **[`webpackImporter`](#webpackimporter)**
- **[`warnRuleAsWarning`](#warnruleaswarning)**

### `implementation`

Type:

```ts
type implementation = object | string;
```

Default: `sass`

The special `implementation` option determines which implementation of Sass to use.

By default the loader resolve the implementation based on your dependencies.
Just add required implementation to `package.json` (`sass` or `node-sass` package) and install dependencies.

Example where the `sass-loader` loader uses the `sass` (`dart-sass`) implementation:

**package.json**

```json
{
  "devDependencies": {
    "sass-loader": "^7.2.0",
    "sass": "^1.22.10"
  }
}
```

Example where the `sass-loader` loader uses the `node-sass` implementation:

**package.json**

```json
{
  "devDependencies": {
    "sass-loader": "^7.2.0",
    "node-sass": "^5.0.0"
  }
}
```

Beware the situation when `node-sass` and `sass` were installed! By default the `sass-loader` prefers `sass`.
In order to avoid this situation you can use the `implementation` option.

The `implementation` options either accepts `sass` (`Dart Sass`) or `node-sass` as a module.

#### `object`

For example, to use Dart Sass, you'd pass:

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              // Prefer `dart-sass`
              implementation: require("sass"),
            },
          },
        ],
      },
    ],
  },
};
```

#### `string`

For example, to use Dart Sass, you'd pass:

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              // Prefer `dart-sass`
              implementation: require.resolve("sass"),
            },
          },
        ],
      },
    ],
  },
};
```

Note that when using `sass` (`Dart Sass`), **synchronous compilation is twice as fast as asynchronous compilation** by default, due to the overhead of asynchronous callbacks.
To avoid this overhead, you can use the [fibers](https://www.npmjs.com/package/fibers) package to call asynchronous importers from the synchronous code path.

We automatically inject the [`fibers`](https://github.com/laverdet/node-fibers) package (setup `sassOptions.fiber`) for `Node.js` less v16.0.0 if is possible (i.e. you need install the [`fibers`](https://github.com/laverdet/node-fibers) package).

> **Warning**
>
> Fibers is not compatible with `Node.js` v16.0.0 or later. Unfortunately, v8 commit [dacc2fee0f](https://github.com/v8/v8/commit/dacc2fee0f815823782a7e432c79c2a7767a4765) is a breaking change and workarounds are non-trivial. ([see introduction to readme](https://github.com/laverdet/node-fibers)).

**package.json**

```json
{
  "devDependencies": {
    "sass-loader": "^7.2.0",
    "sass": "^1.22.10",
    "fibers": "^4.0.1"
  }
}
```

You can disable automatically injecting the [`fibers`](https://github.com/laverdet/node-fibers) package by passing a `false` value for the `sassOptions.fiber` option.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              implementation: require("sass"),
              sassOptions: {
                fiber: false,
              },
            },
          },
        ],
      },
    ],
  },
};
```

You can also pass the `fiber` value using this code:

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              implementation: require("sass"),
              sassOptions: {
                fiber: require("fibers"),
              },
            },
          },
        ],
      },
    ],
  },
};
```

### `sassOptions`

Type:

```ts
type sassOptions =
  | import("sass").LegacyOptions<"async">
  | ((
      content: string | Buffer,
      loaderContext: LoaderContext,
      meta: any
    ) => import("sass").LegacyOptions<"async">);
```

Default: defaults values for Sass implementation

Options for [Dart Sass](http://sass-lang.com/dart-sass) or [Node Sass](https://github.com/sass/node-sass) implementation.

> **Note**
>
> The `charset` option has `true` value by default for `dart-sass`, we strongly discourage change value to `false`, because webpack doesn't support files other than `utf-8`.

> **Note**
>
> The `indentedSyntax` option has `true` value for the `sass` extension.

> **Note**
>
> Options such as `data` and `file` are unavailable and will be ignored.

> ℹ We strongly discourage change `outFile`, `sourceMapContents`, `sourceMapEmbed`, `sourceMapRoot` options because `sass-loader` automatically sets these options when the `sourceMap` option is `true`.

> **Note**
>
> Access to the [loader context](https://webpack.js.org/api/loaders/#the-loader-context) inside the custom importer can be done using the `this.webpackLoaderContext` property.

There is a slight difference between the `sass` (`dart-sass`) and `node-sass` options.

Please consult documentation before using them:

- [Dart Sass documentation](https://sass-lang.com/documentation/js-api/interfaces/Options) for all available `sass` options.
- [Node Sass documentation](https://github.com/sass/node-sass/#options) for all available `node-sass` options.

#### `object`

Use an object for the Sass implementation setup.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              sassOptions: {
                indentWidth: 4,
                includePaths: ["absolute/path/a", "absolute/path/b"],
              },
            },
          },
        ],
      },
    ],
  },
};
```

#### `function`

Allows to setup the Sass implementation by setting different options based on the loader context.

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              sassOptions: (loaderContext) => {
                // More information about available properties https://webpack.js.org/api/loaders/
                const { resourcePath, rootContext } = loaderContext;
                const relativePath = path.relative(rootContext, resourcePath);

                if (relativePath === "styles/foo.scss") {
                  return {
                    includePaths: ["absolute/path/c", "absolute/path/d"],
                  };
                }

                return {
                  includePaths: ["absolute/path/a", "absolute/path/b"],
                };
              },
            },
          },
        ],
      },
    ],
  },
};
```

### `sourceMap`

Type:

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

Default: depends on the `compiler.devtool` value

Enables/Disables generation of source maps.

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.

> ℹ If a `true` the `sourceMap`, `sourceMapRoot`, `sourceMapEmbed`, `sourceMapContents` and `omitSourceMapUrl` from `sassOptions` will be ignored.

**webpack.config.js**

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

> ℹ In some rare cases `node-sass` can output invalid source maps (it is a `node-sass` bug).

> > In order to avoid this, you can try to update `node-sass` to latest version or you can try to set within `sassOptions` the `outputStyle` option to `compressed`.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              sourceMap: true,
              sassOptions: {
                outputStyle: "compressed",
              },
            },
          },
        ],
      },
    ],
  },
};
```

### `additionalData`

Type:

```ts
type additionalData =
  | string
  | ((content: string | Buffer, loaderContext: LoaderContext) => string);
```

Default: `undefined`

Prepends `Sass`/`SCSS` code before the actual entry file.
In this case, the `sass-loader` will not override the `data` option but just **prepend** the entry's content.

This is especially useful when some of your Sass variables depend on the environment:

#### `string`

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              additionalData: "$env: " + process.env.NODE_ENV + ";",
            },
          },
        ],
      },
    ],
  },
};
```

#### `function`

##### Sync

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              additionalData: (content, loaderContext) => {
                // More information about available properties https://webpack.js.org/api/loaders/
                const { resourcePath, rootContext } = loaderContext;
                const relativePath = path.relative(rootContext, resourcePath);

                if (relativePath === "styles/foo.scss") {
                  return "$value: 100px;" + content;
                }

                return "$value: 200px;" + content;
              },
            },
          },
        ],
      },
    ],
  },
};
```

##### Async

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              additionalData: async (content, loaderContext) => {
                // More information about available properties https://webpack.js.org/api/loaders/
                const { resourcePath, rootContext } = loaderContext;
                const relativePath = path.relative(rootContext, resourcePath);

                if (relativePath === "styles/foo.scss") {
                  return "$value: 100px;" + content;
                }

                return "$value: 200px;" + content;
              },
            },
          },
        ],
      },
    ],
  },
};
```

### `webpackImporter`

Type:

```ts
type webpackImporter = boolean;
```

Default: `true`

Enables/Disables the default Webpack importer.

This can improve performance in some cases. Use it with caution because aliases and `@import` at-rules starting with `~` will not work.
You can pass own `importer` to solve this (see [`importer docs`](https://github.com/sass/node-sass#importer--v200---experimental)).

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              webpackImporter: false,
            },
          },
        ],
      },
    ],
  },
};
```

### `warnRuleAsWarning`

Type:

```ts
type warnRuleAsWarning = boolean;
```

Default: `false`

Treats the `@warn` rule as a webpack warning.

> **Note**
>
> It will be `true` by default in the next major release.

**style.scss**

```scss
$known-prefixes: webkit, moz, ms, o;

@mixin prefix($property, $value, $prefixes) {
  @each $prefix in $prefixes {
    @if not index($known-prefixes, $prefix) {
      @warn "Unknown prefix #{$prefix}.";
    }

    -#{$prefix}-#{$property}: $value;
  }
  #{$property}: $value;
}

.tilt {
  // Oops, we typo'd "webkit" as "wekbit"!
  @include prefix(transform, rotate(15deg), wekbit ms);
}
```

The presented code will throw webpack warning instead logging.

To ignore unnecessary warnings you can use the [ignoreWarnings](https://webpack.js.org/configuration/other-options/#ignorewarnings) option.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              warnRuleAsWarning: true,
            },
          },
        ],
      },
    ],
  },
};
```

### `api`

Type:

```ts
type api = "legacy" | "modern";
```

Default: `"legacy"`

Allows you to switch between `legacy` and `modern` API. You can find more information [here](https://sass-lang.com/documentation/js-api).

> **Warning**
>
> "modern" API is experimental, so some features may not work (known: built-in `importer` is not working and files with errors is not watching on initial run), you can follow this [here](https://github.com/webpack-contrib/sass-loader/issues/774).

> **Warning**
>
> The sass options are different for `modern` and `old` APIs. Please look at [docs](https://sass-lang.com/documentation/js-api) how to migrate on new options.

**webpack.config.js**

```js
module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              api: "modern",
              sassOptions: {
                // Your sass options
              },
            },
          },
        ],
      },
    ],
  },
};
```

## How to enable `@debug` output

Defaults, the output of `@debug` messages is disabled.
To enable it, add to **webpack.config.js** following:

```js
module.exports = {
  stats: {
    loggingDebug: ["sass-loader"],
  },
  // ...
};
```

## Examples

### Extracts CSS into separate files

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.

There are two possibilities to extract a style sheet from the bundle:

- [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin)
- [extract-loader](https://github.com/peerigon/extract-loader) (simpler, but specialized on the css-loader's output)

**webpack.config.js**

```js
const MiniCssExtractPlugin = require("mini-css-extract-plugin");

module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          // fallback to style-loader in development
          process.env.NODE_ENV !== "production"
            ? "style-loader"
            : MiniCssExtractPlugin.loader,
          "css-loader",
          "sass-loader",
        ],
      },
    ],
  },
  plugins: [
    new MiniCssExtractPlugin({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: "[name].css",
      chunkFilename: "[id].css",
    }),
  ],
};
```

### Source maps

Enables/Disables generation of source maps.

To enable CSS source maps, you'll need to pass the `sourceMap` option to the `sass-loader` _and_ the css-loader.

**webpack.config.js**

```javascript
module.exports = {
  devtool: "source-map", // any "source-map"-like devtool is possible
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          {
            loader: "css-loader",
            options: {
              sourceMap: true,
            },
          },
          {
            loader: "sass-loader",
            options: {
              sourceMap: true,
            },
          },
        ],
      },
    ],
  },
};
```

If you want to edit the original Sass files inside Chrome, [there's a good blog post](https://medium.com/@toolmantim/getting-started-with-css-sourcemaps-and-in-browser-sass-editing-b4daab987fb0). Checkout [test/sourceMap](https://github.com/webpack-contrib/sass-loader/tree/master/test) for a running example.

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