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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`:
```console
npm install sass-loader sass webpack --save-dev
```
or
```console
yarn add -D sass-loader sass webpack
```
or
```console
pnpm add -D sass-loader sass webpack
```
`sass-loader` requires you to install either [Dart Sass](https://github.com/sass/dart-sass), [Node Sass](https://github.com/sass/node-sass) on your own (more documentation can be found below) or [Sass Embedded](https://github.com/sass/embedded-host-node).
This allows you to control the versions of all your dependencies, and to choose which Sass implementation to use.
> **Note**
>
> We highly recommend using [Dart Sass](https://github.com/sass/dart-sass).
> **Warning**
>
> [Node Sass](https://github.com/sass/node-sass) does not work with [Yarn PnP](https://classic.yarnpkg.com/en/docs/pnp/) feature and doesn't support [@use rule](https://sass-lang.com/documentation/at-rules/use).
> **Warning**
>
> [Sass Embedded](https://github.com/sass/embedded-host-node) is experimental and in `beta`, therefore some features may not work
Chain the `sass-loader` with the [css-loader](https://github.com/webpack-contrib/css-loader) and the [style-loader](https://github.com/webpack-contrib/style-loader) to immediately apply all styles to the DOM or the [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) to extract it into a separate file.
Then add the loader to your Webpack configuration. For example:
**app.js**
```js
import "./style.scss";
```
**style.scss**
```scss
$body-color: red;
body {
color: $body-color;
}
```
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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](https://webpack.js.org/concepts/module-resolution/).
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`.
```scss
@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`](https://webpack.js.org/configuration/resolve/#resolvemodules).
Prepending module paths with a `~` tells webpack to search through [`node_modules`](https://webpack.js.org/configuration/resolve/#resolvemodules).
```scss
@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](https://github.com/sass/libsass/issues/532), 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](https://github.com/bholloway/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](https://github.com/twbs/bootstrap-sass) for example has an `$icon-font-path`.
## Options
- **[`implementation`](#implementation)**
- **[`sassOptions`](#sassoptions)**
- **[`sourceMap`](#sourcemap)**
- **[`additionalData`](#additionaldata)**
- **[`webpackImporter`](#webpackimporter)**
- **[`warnRuleAsWarning`](#warnruleaswarning)**
### `implementation`
Type:
```ts
type implementation = object | string;
```
Default: `sass`
The special `implementation` option determines which implementation of Sass to use.
By default the loader resolve the implementation based on your dependencies.
Just add required implementation to `package.json` (`sass` or `node-sass` package) and install dependencies.
Example where the `sass-loader` loader uses the `sass` (`dart-sass`) implementation:
**package.json**
```json
{
"devDependencies": {
"sass-loader": "^7.2.0",
"sass": "^1.22.10"
}
}
```
Example where the `sass-loader` loader uses the `node-sass` implementation:
**package.json**
```json
{
"devDependencies": {
"sass-loader": "^7.2.0",
"node-sass": "^5.0.0"
}
}
```
Beware the situation when `node-sass` and `sass` were installed! By default the `sass-loader` prefers `sass`.
In order to avoid this situation you can use the `implementation` option.
The `implementation` options either accepts `sass` (`Dart Sass`) or `node-sass` as a module.
#### `object`
For example, to use Dart Sass, you'd pass:
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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:
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
// Prefer `dart-sass`
implementation: require.resolve("sass"),
},
},
],
},
],
},
};
```
Note that when using `sass` (`Dart Sass`), **synchronous compilation is twice as fast as asynchronous compilation** by default, due to the overhead of asynchronous callbacks.
To avoid this overhead, you can use the [fibers](https://www.npmjs.com/package/fibers) package to call asynchronous importers from the synchronous code path.
We automatically inject the [`fibers`](https://github.com/laverdet/node-fibers) package (setup `sassOptions.fiber`) for `Node.js` less v16.0.0 if is possible (i.e. you need install the [`fibers`](https://github.com/laverdet/node-fibers) package).
> **Warning**
>
> Fibers is not compatible with `Node.js` v16.0.0 or later. Unfortunately, v8 commit [dacc2fee0f](https://github.com/v8/v8/commit/dacc2fee0f815823782a7e432c79c2a7767a4765) is a breaking change and workarounds are non-trivial. ([see introduction to readme](https://github.com/laverdet/node-fibers)).
**package.json**
```json
{
"devDependencies": {
"sass-loader": "^7.2.0",
"sass": "^1.22.10",
"fibers": "^4.0.1"
}
}
```
You can disable automatically injecting the [`fibers`](https://github.com/laverdet/node-fibers) package by passing a `false` value for the `sassOptions.fiber` option.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
implementation: require("sass"),
sassOptions: {
fiber: require("fibers"),
},
},
},
],
},
],
},
};
```
### `sassOptions`
Type:
```ts
type sassOptions =
| import("sass").LegacyOptions<"async">
| ((
content: string | Buffer,
loaderContext: LoaderContext,
meta: any
) => import("sass").LegacyOptions<"async">);
```
Default: defaults values for Sass implementation
Options for [Dart Sass](http://sass-lang.com/dart-sass) or [Node Sass](https://github.com/sass/node-sass) implementation.
> **Note**
>
> The `charset` option has `true` value by default for `dart-sass`, we strongly discourage change value to `false`, because webpack doesn't support files other than `utf-8`.
> **Note**
>
> The `indentedSyntax` option has `true` value for the `sass` extension.
> **Note**
>
> Options such as `data` and `file` are unavailable and will be ignored.
> ℹ We strongly discourage change `outFile`, `sourceMapContents`, `sourceMapEmbed`, `sourceMapRoot` options because `sass-loader` automatically sets these options when the `sourceMap` option is `true`.
> **Note**
>
> Access to the [loader context](https://webpack.js.org/api/loaders/#the-loader-context) inside the custom importer can be done using the `this.webpackLoaderContext` property.
There is a slight difference between the `sass` (`dart-sass`) and `node-sass` options.
Please consult documentation before using them:
- [Dart Sass documentation](https://sass-lang.com/documentation/js-api/interfaces/Options) for all available `sass` options.
- [Node Sass documentation](https://github.com/sass/node-sass/#options) for all available `node-sass` options.
#### `object`
Use an object for the Sass implementation setup.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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.
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
sassOptions: (loaderContext) => {
// More information about available properties https://webpack.js.org/api/loaders/
const { resourcePath, rootContext } = loaderContext;
const relativePath = path.relative(rootContext, resourcePath);
if (relativePath === "styles/foo.scss") {
return {
includePaths: ["absolute/path/c", "absolute/path/d"],
};
}
return {
includePaths: ["absolute/path/a", "absolute/path/b"],
};
},
},
},
],
},
],
},
};
```
### `sourceMap`
Type:
```ts
type sourceMap = boolean;
```
Default: depends on the `compiler.devtool` value
Enables/Disables generation of source maps.
By default generation of source maps depends on the [`devtool`](https://webpack.js.org/configuration/devtool/) option.
All values enable source map generation except `eval` and `false` value.
> ℹ If a `true` the `sourceMap`, `sourceMapRoot`, `sourceMapEmbed`, `sourceMapContents` and `omitSourceMapUrl` from `sassOptions` will be ignored.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
sourceMap: true,
sassOptions: {
outputStyle: "compressed",
},
},
},
],
},
],
},
};
```
### `additionalData`
Type:
```ts
type additionalData =
| string
| ((content: string | Buffer, loaderContext: LoaderContext) => string);
```
Default: `undefined`
Prepends `Sass`/`SCSS` code before the actual entry file.
In this case, the `sass-loader` will not override the `data` option but just **prepend** the entry's content.
This is especially useful when some of your Sass variables depend on the environment:
#### `string`
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
additionalData: "$env: " + process.env.NODE_ENV + ";",
},
},
],
},
],
},
};
```
#### `function`
##### Sync
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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
```js
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 "$value: 200px;" + content;
},
},
},
],
},
],
},
};
```
### `webpackImporter`
Type:
```ts
type webpackImporter = boolean;
```
Default: `true`
Enables/Disables the default Webpack importer.
This can improve performance in some cases. Use it with caution because aliases and `@import` at-rules starting with `~` will not work.
You can pass own `importer` to solve this (see [`importer docs`](https://github.com/sass/node-sass#importer--v200---experimental)).
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
webpackImporter: false,
},
},
],
},
],
},
};
```
### `warnRuleAsWarning`
Type:
```ts
type warnRuleAsWarning = boolean;
```
Default: `false`
Treats the `@warn` rule as a webpack warning.
> **Note**
>
> It will be `true` by default in the next major release.
**style.scss**
```scss
$known-prefixes: webkit, moz, ms, o;
@mixin prefix($property, $value, $prefixes) {
@each $prefix in $prefixes {
@if not index($known-prefixes, $prefix) {
@warn "Unknown prefix #{$prefix}.";
}
-#{$prefix}-#{$property}: $value;
}
#{$property}: $value;
}
.tilt {
// Oops, we typo'd "webkit" as "wekbit"!
@include prefix(transform, rotate(15deg), wekbit ms);
}
```
The presented code will throw webpack warning instead logging.
To ignore unnecessary warnings you can use the [ignoreWarnings](https://webpack.js.org/configuration/other-options/#ignorewarnings) option.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
warnRuleAsWarning: true,
},
},
],
},
],
},
};
```
### `api`
Type:
```ts
type api = "legacy" | "modern";
```
Default: `"legacy"`
Allows you to switch between `legacy` and `modern` API. You can find more information [here](https://sass-lang.com/documentation/js-api).
> **Warning**
>
> "modern" API is experimental, so some features may not work (known: built-in `importer` is not working and files with errors is not watching on initial run), you can follow this [here](https://github.com/webpack-contrib/sass-loader/issues/774).
> **Warning**
>
> The sass options are different for `modern` and `old` APIs. Please look at [docs](https://sass-lang.com/documentation/js-api) how to migrate on new options.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/i,
use: [
"style-loader",
"css-loader",
{
loader: "sass-loader",
options: {
api: "modern",
sassOptions: {
// Your sass options
},
},
},
],
},
],
},
};
```
## How to enable `@debug` output
Defaults, the output of `@debug` messages is disabled.
To enable it, add to **webpack.config.js** following:
```js
module.exports = {
stats: {
loggingDebug: ["sass-loader"],
},
// ...
};
```
## Examples
### Extracts CSS into separate files
For production builds it's recommended to extract the CSS from your bundle being able to use parallel loading of CSS/JS resources later on.
There are four possibilities to extract a style sheet from the bundle:
#### 1. [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin)
**webpack.config.js**
```js
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
module.exports = {
module: {
rules: [
{
test: /\.s[ac]ss$/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",
}),
],
};
```
#### 2. [Asset Modules](https://webpack.js.org/guides/asset-modules/)
**webpack.config.js**
```js
module.exports = {
entry: [__dirname + "/src/scss/app.scss"],
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
use: [],
},
{
test: /\.scss$/,
exclude: /node_modules/,
type: "asset/resource",
generator: {
filename: "bundle.css",
},
use: ["sass-loader"],
},
],
},
};
```
#### 3. [extract-loader](https://github.com/peerigon/extract-loader) (simpler, but specialized on the css-loader's output)
#### 4. [file-loader](https://github.com/webpack-contrib/file-loader) (deprecated--should only be used in Webpack v4)
**webpack.config.js**
```js
module.exports = {
entry: [__dirname + "/src/scss/app.scss"],
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
use: [],
},
{
test: /\.scss$/,
exclude: /node_modules/,
use: [
{
loader: "file-loader",
options: { outputPath: "css/", name: "[name].min.css" },
},
"sass-loader",
],
},
],
},
};
```
(source: https://stackoverflow.com/a/60029923/2969615)
### 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**
```javascript
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](https://medium.com/@toolmantim/getting-started-with-css-sourcemaps-and-in-browser-sass-editing-b4daab987fb0). Checkout [test/sourceMap](https://github.com/webpack-contrib/sass-loader/tree/master/test) for a running example.
## Contributing
Please take a moment to read our contributing guidelines if you haven't yet done so.
[CONTRIBUTING](./.github/CONTRIBUTING.md)
## License
[MIT](./LICENSE)
[npm]: https://img.shields.io/npm/v/sass-loader.svg
[npm-url]: https://npmjs.com/package/sass-loader
[node]: https://img.shields.io/node/v/sass-loader.svg
[node-url]: https://nodejs.org
[tests]: https://github.com/webpack-contrib/sass-loader/workflows/sass-loader/badge.svg
[tests-url]: https://github.com/webpack-contrib/sass-loader/actions
[cover]: https://codecov.io/gh/webpack-contrib/sass-loader/branch/master/graph/badge.svg
[cover-url]: https://codecov.io/gh/webpack-contrib/sass-loader
[discussion]: https://img.shields.io/github/discussions/webpack/webpack
[discussion-url]: https://github.com/webpack/webpack/discussions
[size]: https://packagephobia.now.sh/badge?p=sass-loader
[size-url]: https://packagephobia.now.sh/result?p=sass-loader