webpack/sass-loader

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

or

yarn add -D sass-loader sass webpack

or

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 or Sass Embedded on your own (more documentation can be found below).

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.

Chain the sass-loader with the css-loader and the style-loader to immediately apply all styles to the DOM, or with 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 (e.g., via CLI or an npm script).

The style option in production mode

For production mode, the style option defaults 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, URLs 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.

Options

• implementation
• sassOptions
• sourceMap
• additionalData
• webpackImporter
• warnRuleAsWarning
• api

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 or sass-embedded package) and install dependencies.

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

package.json

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

Example where the sass-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:

1. sass-embedded
2. 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").StringOptionsWithImporter<"async">
  | ((
      content: string | Buffer,
      loaderContext: LoaderContext,
      meta: any,
    ) => import("sass").StringOptionsWithImporter<"async">);

Default: defaults values for Sass implementation

Options for Dart Sass or Sass Embedded 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 option is scss for the scss extension, indented for the sass extension, and css for the css extension.

[!NOTE]

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

ℹ We strongly discourage changing the sourceMap option because sass-loader sets it automatically when the sourceMap option is true.

Please consult their respective documentation before using them:

• Dart Sass documentation for all available sass options.
• Sass Embedded documentation for all available sass-embedded 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 option 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,
            },
          },
        ],
      },
    ],
  },
};

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          "style-loader",
          "css-loader",
          {
            loader: "sass-loader",
            options: {
              sourceMap: true,
              sassOptions: {
                style: "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 Sass importer documentation).

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 of 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 = "auto" | "modern" | "modern-compiler";

Default: "auto" for sass (dart-sass) and sass-embedded

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

When "auto" is used, the loader picks "modern-compiler" whenever the implementation exposes initAsyncCompiler (i.e. recent versions of sass and sass-embedded) and falls back to "modern" otherwise. Combined with sass-embedded, this yields the best build performance out of the box.

[!NOTE]

Using modern-compiler and sass-embedded together significantly improves performance and decreases build time. They are now selected automatically by the default "auto" API.

[!NOTE]

The legacy Sass JS API is no longer supported. If you were using api: "legacy", please migrate to the modern API. See the Sass JS API docs to learn how to migrate.

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 is 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 enable parallel loading of CSS/JS resources.

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

const path = require("node:path");

module.exports = {
  entry: [path.resolve(__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

const path = require("node:path");

module.exports = {
  entry: [path.resolve(__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 both 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,
            },
          },
        ],
      },
    ],
  },
};

If you want to edit the original Sass files inside Chrome, there's a good blog post. Checkout test/sourceMap for a working example.

Contributing

We welcome all contributions! If you're new here, please take a moment to review our contributing guidelines before submitting issues or pull requests.

CONTRIBUTING

License

MIT