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Description

Compiles Sass to CSS

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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

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

ℹ️ We highly recommend using Dart Sass.

Node Sass does not work with Yarn PnP feature 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.

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
.
@import "bootstrap";

Using

~
is deprecated and can be removed from your code (we recommend it), 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 it 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 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

| Name | Type | Default | Description | | :---------------------------------------: | :------------------: | :-------------------------------------: | :---------------------------------------------------------------- | |

implementation
|

{Object\|String}
|
sass
| Setup Sass implementation to use. | |
sassOptions
|
{Object\|Function}
| defaults values for Sass implementation | Options for Sass. | |
sourceMap
|
{Boolean}
|
compiler.devtool
| Enables/Disables generation of source maps. | |
additionalData
|
{String\|Function}
|
undefined
| Prepends/Appends
Sass
/
SCSS
code before the actual entry file. | |
webpackImporter
|
{Boolean}
|
true
| Enables/Disables the default Webpack importer. |

implementation

Type:

Object | String
Default:
sass

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
(
sass
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"
  }
}

Beware the situation when

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

The

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

Object

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"),
            },
          },
        ],
      },
    ],
  },
};

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`
              implementation: require.resolve("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
) for
Node.js
less v16.0.0 if is possible (i.e. you need install the
fibers
package).

Fibers is not compatible with

Node.js
v16.0.0 or later (see introduction to readme).

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
Default: defaults values for Sass implementation

Options for Dart Sass or Node Sass implementation.

ℹ️ The

charset
option has
true
value by default for
dart-sass
, we strongly discourage change value to
false
, because webpack doesn't support files other than
utf-8
.

ℹ️ The

indentedSyntax
option has
true
value for the
sass
extension.

ℹ️ Options such as

data
and
file
are unavailable and will be ignored.

ℹ We strongly discourage change

outFile
,
sourceMapContents
,
sourceMapEmbed
,
sourceMapRoot
options because
sass-loader
automatically sets these options when the
sourceMap
option is
true
.

ℹ️ Access to the loader context inside the custom importer can be done using the

this.webpackLoaderContext
property.

There is a slight difference between the

sass
(
dart-sass
) and
node-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"],
            };
          },
        },
      },
    ],
  },
],

}, };

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.

ℹ If a

true
the
sourceMap
,
sourceMapRoot
,
sourceMapEmbed
,
sourceMapContents
and
omitSourceMapUrl
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:

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 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:

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: /\.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 running example.

Contributing

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

CONTRIBUTING

License

MIT

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