lepu-test-platform-web/node_modules/sass-loader/README.md

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

The sass-loader requires you to install either Node Sass or Dart Sass on your own (more documentation you can find below). This allows you to control the versions of all your dependencies, and to choose which Sass implementation to use.

• node sass
• dart sass

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 config. For example:

file.js

import style from './style.scss';

file.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',
        ],
      },
    ],
  },
};

And run webpack via your preferred method.

Resolving import at-rules

The 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. The webpack needs to distinguish between bootstrap and ~bootstrap because CSS and Sass files have no special syntax for importing relative files. Writing @import "file" is the same as @import "./file";

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 the 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

By default all options passed to loader also passed to to Node Sass or Dart Sass

ℹ️ The indentedSyntax option has true value for the sass extension. ℹ️ Options such as file and outFile are unavailable. ℹ️ Only the "expanded" and "compressed" values of outputStyle are supported for dart-sass. ℹ We recommend don't use sourceMapContents, sourceMapEmbed, sourceMapRoot options because loader automatically setup this options.

There is a slight difference between the node-sass and sass options. We recommend look documentation before used them:

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

webpack.config.js

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

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 was installed, by default the sass-loader prefers node-sass, to avoid this situation use the implementation option.

It takes either node-sass or sass (Dart Sass) 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.

To enable this, pass the Fiber class to the 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'),
              fiber: require('fibers'),
            },
          },
        ],
      },
    ],
  },
};

data

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$/i,
        use: [
          'style-loader',
          'css-loader',
          {
            loader: 'sass-loader',
            options: {
              data: '$env: ' + process.env.NODE_ENV + ';',
            },
          },
        ],
      },
    ],
  },
};

Function

module.exports = {
  module: {
    rules: [
      {
        test: /\.s[ac]ss$/i,
        use: [
          'style-loader',
          'css-loader',
          {
            loader: 'sass-loader',
            options: {
              data: (loaderContext) => {
                // More information about avalaible options 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: false

Enables/Disables generation of source maps.

They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS source maps do not).

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 case node-sass can output invalid source maps (it is node-sass bug), to avoid try to update node-sass to latest version or you can try to set the outputStyle option to compressed value.

webpackImporter

Type: Boolean Default: true

Allows to disable default webpack importer.

This can improve performance in some cases. Use it with caution because aliases and @import at-rules starts with ~ will not work, but 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:

• mini-css-extract-plugin (use this, when using webpack 4 configuration. Works in all use-cases)
• extract-loader (simpler, but specialized on the css-loader's output)

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

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