sass-loader

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

Getting Started

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

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

yarn add -D sass-loader sass webpack

pnpm add -D sass-loader sass webpack

Note

To enable CSS processing in your project, you need to install style-loader and css-loader via npm i style-loader css-loader.

sass-loader requires you to install either Dart Sass, Node Sass on your own (more documentation can be found below) or Sass Embedded.

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

Note

We highly recommend using Sass Embedded or Dart Sass.

Warning

Node Sass does not work with Yarn PnP and doesn't support @use rule.

Chain the sass-loader with the css-loader and the style-loader to immediately apply all styles to the DOM or the mini-css-extract-plugin to extract it into a separate file.

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

app.js

import "./style.scss";

style.scss

$body-color: red;

body {
  color: $body-color;
}

webpack.config.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.

The `style` (new API, by default since 16 version) and `outputStyle` (old API) options in `production` mode

For production mode, the style (new API, by default since 16 version) and outputStyle (old API) options default to compressed unless otherwise specified in sassOptions.

Resolving `import` and `use` at-rules

Webpack provides an advanced mechanism to resolve files.

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

@import "bootstrap";

Using ~ is deprecated and should be removed from your code, 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.

Prepending module paths with a ~ tells webpack to search through node_modules.

@import "~bootstrap";

It's important to prepend the path 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, 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 might be surprised by this first issue, as 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 two solutions to this problem:

Add the missing url rewriting using the 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 for example has an $icon-font-path.

`implementation`

Type:

type implementation = object | string;

Default: sass

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

By default, the loader resolves the implementation based on your dependencies. Just add the desired implementation to your package.json (sass, sass-embedded, or node-sass package) and install dependencies.

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

package.json

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

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

package.json

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

Example where the sass-loader loader uses the sass-embedded implementation:

package.json

{
  "devDependencies": {
    "sass-loader": "^7.2.0",
    "sass": "^1.22.10"
  },
  "optionalDependencies": {
    "sass-embedded": "^1.70.0"
  }
}

Note

Using optionalDependencies means that sass-loader can fallback to sass when running on an operating system not supported by sass-embedded

Be aware of the order that sass-loader will resolve the implementation:

sass-embedded
sass
node-sass

You can specify a specific implementation by using the implementation option, which accepts one of the above values.

`object`

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

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

`string`

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

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

`sassOptions`

Type:

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 or Node Sass implementation.

Note

The charset option is true by default for dart-sass, we strongly discourage setting this to false, because webpack doesn't support files other than utf-8.

Note

The syntax (new API, by default since 16 version)andindentedSyntax(old API) option isscssfor thescssextension,indentedfor thesassextension andcssfor thecss` extension.

Note

Options such as data and file are unavailable and will be ignored.

ℹ We strongly discourage changing the sourceMap (new API, by default since 16 version), outFile (old API), sourceMapContents (old API), sourceMapEmbed (old API), and sourceMapRoot (old API) options because sass-loader sets these automatically when the sourceMap option is true.

Note

Access to the loader context inside the custom importer can be done using the this.webpackLoaderContext property.

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

Please consult their respective documentation before using them:

Dart Sass documentation for all available sass options.
Sass Embedded documentation for all available sass options.
Node Sass documentation for all available node-sass options.
Sass Embedded documentation for all available sass options.

`object`

Use an object for the Sass implementation setup.

webpack.config.js

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

`function`

Allows configuring the Sass implementation with different options based on the loader context.

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 {
                    loadPaths: ["absolute/path/c", "absolute/path/d"],
                  };
                }

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

`sourceMap`

Type:

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 option. All values enable source map generation except eval and false.

ℹ If true, the sourceMap (new API, by default since 16 version), outFile (old API), sourceMapContents (old API), sourceMapEmbed (old API), and sourceMapRoot (old API) from sassOptions will be ignored.

webpack.config.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

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:

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`

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

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

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:

type webpackImporter = boolean;

Default: true

Enables/Disables the default webpack importer.

This can improve performance in some cases, though use it with caution because aliases and @import at-rules starting with ~ will not work. You can pass your own importer to solve this (see importer docs).

webpack.config.js

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

`warnRuleAsWarning`

Type:

type warnRuleAsWarning = boolean;

Default: true

Treats the @warn rule as a webpack warning.

style.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 a webpack warning instead logging.

To ignore unnecessary warnings you can use the ignoreWarnings option.

webpack.config.js

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

`api`

Type:

type api = "legacy" | "modern" | "modern-compiler";

Default: "modern" for sass (dart-sass) and sass-embedded, or "legacy" for node-sass

Allows you to switch between the legacy and modern APIs. You can find more information here. The modern-compiler option enables the modern API with support for Shared Resources.

Note

Using modern-compiler and sass-embedded together significantly improve performance and decrease built time. We strongly recommend their use. We will enable them by default in a future major release.

Warning

The sass options are different for the legacy and modern APIs. Please look at docs how to migrate to the modern options.

webpack.config.js

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

How to enable `@debug` output

By default, the output of @debug messages are disabled. Add the following to webpack.config.js to enable them:

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 to be able to use parallel loading of CSS/JS resources later on.

There are four recommended ways to extract a stylesheet from a bundle:

1. mini-css-extract-plugin

webpack.config.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",
    }),
  ],
};

2. Asset Modules

webpack.config.js

module.exports = {
  entry: [__dirname + "/src/scss/app.scss"],
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: [],
      },
      {
        test: /\.scss$/,
        exclude: /node_modules/,
        type: "asset/resource",
        generator: {
          filename: "bundle.css",
        },
        use: ["sass-loader"],
      },
    ],
  },
};

3. extract-loader (simpler, but specialized on the css-loader's output)

4. file-loader (deprecated--should only be used in webpack v4)

webpack.config.js

module.exports = {
  entry: [__dirname + "/src/scss/app.scss"],
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: [],
      },
      {
        test: /\.scss$/,
        exclude: /node_modules/,
        use: [
          {
            loader: "file-loader",
            options: { outputPath: "css/", name: "[name].min.css" },
          },
          "sass-loader",
        ],
      },
    ],
  },
};

(source: https://stackoverflow.com/a/60029923/2969615)

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

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,
            },
          },
        ],
      },
    ],
  },
};