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 node-sass webpack --save-dev

sass-loader requires you to install either Node Sass or Dart Sass 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.

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.

Resolving import 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. Thus you can import your Sass modules from node_modules. Just prepend them with a ~ to tell Webpack that this is not a relative import:

@import '~bootstrap';

It's important to only prepend it with ~, 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 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. 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

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 (node-sass or 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": "^4.0.0"
  }
}

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

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

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`
              implementation: require('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 package to call asynchronous importers from the synchronous code path.

We automatically inject the fibers package (setup sassOptions.fiber) if is possible (i.e. you need install the fibers package).

package.json

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

You can disable automatically injecting the fibers package by passing a false value for the sassOptions.fiber option.

webpack.config.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

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: Object|Function

Options for Node Sass or Dart Sass implementation.

ℹ️ The indentedSyntax option has true value for the sass extension.

ℹ️ Options such as file and outFile are unavailable.

ℹ We recommend not to use the sourceMapContents, sourceMapEmbed, sourceMapRoot options because sass-loader automatically sets these options.

There is a slight difference between the node-sass and sass (Dart Sass) options. Please consult documentation before using them:

Object

Use and 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: {
                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.

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

prependData

Type: String|Function 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 append the entry's content.

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

ℹ Since you're injecting code, this will break the source mappings in your entry file. Often there's a simpler solution than this, like multiple Sass entry files.

String 

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

Function 

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

                return '$value: 200px;';
              },
            },
          },
        ],
      },
    ],
  },
};

sourceMap

Type: 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 value.

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 the outputStyle option to compressed.

webpackImporter

Type: 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).

webpack.config.js

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

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:

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',
    }),
  ],
};

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: /\.scss$/,
        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 running example.

Contributing

Please take a moment to read our contributing guidelines if you haven't yet done so.

CONTRIBUTING

License

MIT

© JS Foundation and other contributors
Licensed under the Creative Commons Attribution License 4.0.
https://v4.webpack.js.org/loaders/sass-loader