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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 recommend using Dart Sass.
⚠ Node Sass does not work with Yarn PnP feature.
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: [
"style-loader",
"css-loader",
"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
$icon-font-path
.
Options
Name | Type | Default | Description |
---|
implementation | {Object} | sass | Setup Sass implementation to use. |
sassOptions | {Object|Function} | defaults values for Sass implementation | Options for Sass. |
sourceMap | {Boolean} | compiler.devtool | Enables/Disables generation of source maps. |
additionalData | {String|Function} | undefined | Prepends/Appends Sass /SCSS code before the actual entry file. |
webpackImporter | {Boolean} | true | Enables/Disables the default Webpack importer. |
implementation
Type: Object
Default: sass
The special implementation
option determines which implementation of Sass to use.
By default the loader resolve the implementation based on your dependencies.
Just add required implementation to package.json
(sass
or node-sass
package) and install dependencies.
Example where the sass-loader
loader uses the sass
(dart-sass
) implementation:
package.json
{
"devDependencies": {
"sass-loader": "^7.2.0",
"sass": "^1.22.10"
}
}
Example where the sass-loader
loader uses the node-sass
implementation:
package.json
{
"devDependencies": {
"sass-loader": "^7.2.0",
"node-sass": "^5.0.0"
}
}
Beware the situation when node-sass
and sass
were installed! By default the sass-loader
prefers sass
.
In order to avoid this situation you can use the implementation
option.
The implementation
options either accepts sass
(Dart Sass
) or node-sass
as a module.
For example, to use Dart Sass, you'd pass:
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
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
Default: defaults values for Sass implementation
Options for Dart Sass or Node Sass implementation.
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 recommend not to set the 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) => {
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$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
additionalData: (content, loaderContext) => {
const { resourcePath, rootContext } = loaderContext;
const relativePath = path.relative(rootContext, resourcePath);
if (relativePath === "styles/foo.scss") {
return "$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) => {
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$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
webpackImporter: false,
},
},
],
},
],
},
};
Examples
For production builds it's recommended to extract the CSS from your bundle being able to use parallel loading of CSS/JS resources later on.
There are two possibilities to extract a style sheet from the bundle:
webpack.config.js
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
process.env.NODE_ENV !== "production"
? "style-loader"
: MiniCssExtractPlugin.loader,
"css-loader",
"sass-loader",
],
},
],
},
plugins: [
new MiniCssExtractPlugin({
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",
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