sass-loader

What is sass-loader?

The sass-loader npm package is a loader for webpack that allows you to preprocess .scss or .sass files to standard CSS. It uses the Sass compiler to convert Sass code into CSS, and then webpack can bundle the resulting CSS into your final build.

What are sass-loader's main functionalities?

Compiling Sass/SCSS to CSS

This webpack configuration snippet demonstrates how to set up sass-loader in conjunction with css-loader and style-loader to process .scss files.

module.exports = {
  module: {
    rules: [
      {
        test: /\.scss$/,
        use: [
          'style-loader',
          'css-loader',
          'sass-loader'
        ]
      }
    ]
  }
};

Source Maps

This code enables source maps for easier debugging of Sass files. It configures sass-loader to generate source maps so that the browser dev tools can display the original Sass code instead of the compiled CSS.

module.exports = {
  module: {
    rules: [
      {
        test: /\.scss$/,
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: { sourceMap: true }
          },
          {
            loader: 'sass-loader',
            options: { sourceMap: true }
          }
        ]
      }
    ]
  }
};

Custom Functions

This example shows how to add custom functions to the Sass compilation process. The custom 'pow' function can be used within Sass files to compute powers.

const sass = require('sass');

module.exports = {
  module: {
    rules: [
      {
        test: /\.scss$/,
        use: [
          'style-loader',
          'css-loader',
          {
            loader: 'sass-loader',
            options: {
              sassOptions: {
                functions: {
                  'pow($base, $exponent)': function(base, exponent) {
                    return new sass.types.Number(Math.pow(base.getValue(), exponent.getValue()));
                  }
                }
              }
            }
          }
        ]
      }
    ]
  }
};

Other packages similar to sass-loader

node-sass

node-sass is a library that provides binding for Node.js to the Sass compiler. It allows you to natively compile .scss files to css at incredible speed. However, node-sass is deprecated in favor of Dart Sass.

postcss-loader

postcss-loader is a tool that uses PostCSS to process CSS with JavaScript plugins. It can be used for tasks such as autoprefixing, linting, and more. While sass-loader focuses on compiling Sass, postcss-loader is more about post-processing CSS.

less-loader

less-loader is similar to sass-loader but for Less, which is another preprocessor language that extends the capabilities of CSS. It's a loader for webpack that compiles Less to CSS.

stylus-loader

stylus-loader enables webpack to compile Stylus files to CSS. Stylus is another CSS preprocessor scripting language, offering similar features to Sass/SCSS.

README

sass loader for webpack

Install

npm install sass-loader

Usage

Documentation: Using loaders

var css = require("raw!sass!./file.scss");
// => returns compiled css code from file.scss, resolves imports
var css = require("css!sass!./file.scss");
// => returns compiled css code from file.scss, resolves imports and url(...)s

Use in tandem with the style-loader to add the css rules to your document:

require("style!css!sass!./file.scss");

Apply via webpack config

It's recommended to adjust your webpack.config so style!css!sass! is applied automatically on all files ending on .scss:

module.exports = {
  module: {
    loaders: [
      {
        test: /\.scss$/,
        // Query parameters are passed to node-sass
        loader: "style!css!sass?outputStyle=expanded&" +
          "includePaths[]=" +
            (path.resolve(__dirname, "./bower_components")) + "&" +
          "includePaths[]=" +
            (path.resolve(__dirname, "./node_modules"))
      }
    ]
  }
};

Then you only need to write: require("./file.scss"). See node-sass for all available options.

.sass files

For requiring .sass files, add indentedSyntax=sass as a loader option:

module.exports = {
  module: {
    loaders: [
      {
        test: /\.scss$/,
        // Passing indentedSyntax query param to node-sass
        loader: "style!css!sass?indentedSyntax=sass"
      }
    ]
  }
};

Source maps

Source maps are only available in conjunction with the extract-text-webpack-plugin. Use that plugin to extract the CSS code from the generated JS bundle into a separate file (which even improves the perceived performance because JS and CSS are loaded in parallel).

Then your webpack.config.js should look like this:

var ExtractTextPlugin = require('extract-text-webpack-plugin');

module.exports = {
    ...
    // must be 'source-map' or 'inline-source-map'
    devtool: 'source-map',
    module: {
        loaders: [
            {
                test: /\.scss$/,
                loader: ExtractTextPlugin.extract(
                    // activate source maps via loader query
                    'css?sourceMap!' +
                    'sass?sourceMap'
                )
            }
        ]
    },
    plugins: [
        // extract into separate 'styles.css'
        new ExtractTextPlugin('styles.css')
    ]
};

If you want to view the original SASS files inside Chrome and even edit it, there's a good blog post. Checkout test/sourceMap for a running example. Make sure to serve the content with an HTTP server.

Caveats

Currently the sass-loader does not follow all of the webpack loader guidelines. The general problem is that the entry scss-file is passed to node-sass which does pretty much the rest. Thus @import statements inside your scss-files cannot be resolved by webpack's resolver. However, there is an issue for that missing feature in libsass.

License

MIT (http://www.opensource.org/licenses/mit-license.php)