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css-loader
Advanced tools
The css-loader is a loader for webpack that interprets `@import` and `url()` like `import/require()` and will resolve them. It allows you to load CSS files with JavaScript and use CSS modules for local scope CSS.
Interpreting @import and url()
Allows importing CSS within JavaScript modules using @import and url() which will be resolved by webpack.
import './style.css';
CSS Modules
Enables the use of CSS Modules, where CSS classes are imported as an object of strings, allowing for local scope and composition of CSS classes.
import styles from './style.module.css'; console.log(styles.className);
Source Maps
Supports generation of source maps to enable debugging of CSS by linking the transformed code back to the original source.
module.exports = { module: { rules: [{ test: /\.css$/, use: ['style-loader', { loader: 'css-loader', options: { sourceMap: true } }] }] } };
Minification
In combination with other tools like CssMinimizerPlugin, it can be used to minify CSS for production builds.
module.exports = { optimization: { minimizer: ['...', new CssMinimizerPlugin()] } };
Import Loaders
Allows to configure how many loaders before css-loader should be applied to @imported resources.
module.exports = { module: { rules: [{ test: /\.css$/, use: ['style-loader', { loader: 'css-loader', options: { importLoaders: 1 } }, 'postcss-loader'] }] } };
Injects CSS into the DOM using multiple <style> tags. It is often used in conjunction with css-loader.
Loads and compiles Sass/SCSS files. It extends css-loader's functionality to work with Sass/SCSS syntax.
Processes Less files and compiles them to CSS. Similar to sass-loader, it's specific to Less preprocessor language.
Processes CSS with PostCSS, a tool for transforming CSS with JavaScript plugins. It can be used after css-loader to apply various transformations and optimizations.
Extracts CSS into separate files. It creates a CSS file per JS file which contains CSS. It is used for CSS splitting, and is more performant than style-loader for production builds.
The css-loader
interprets @import
and url()
like import/require()
and will resolve them.
To begin, you'll need to install css-loader
:
npm install --save-dev css-loader
Then add the plugin to your webpack
config. For example:
file.js
import css from 'file.css';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: ['style-loader', 'css-loader'],
},
],
},
};
Good loaders for requiring your assets are the file-loader and the url-loader which you should specify in your config (see below).
And run webpack
via your preferred method.
toString
You can also use the css-loader results directly as a string, such as in Angular's component style.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: ['to-string-loader', 'css-loader'],
},
],
},
};
or
const css = require('./test.css').toString();
console.log(css); // {String}
If there are SourceMaps, they will also be included in the result string.
If, for one reason or another, you need to extract CSS as a plain string resource (i.e. not wrapped in a JS module) you might want to check out the extract-loader. It's useful when you, for instance, need to post process the CSS as a string.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: [
'handlebars-loader', // handlebars loader expects raw resource string
'extract-loader',
'css-loader',
],
},
],
},
};
Name | Type | Default | Description |
---|---|---|---|
url | {Boolean|Function} | true | Enable/Disable url() handling |
import | {Boolean\/Function} | true | Enable/Disable @import handling |
modules | {Boolean|String} | false | Enable/Disable CSS Modules and setup mode |
localIdentName | {String} | [hash:base64] | Configure the generated ident |
sourceMap | {Boolean} | false | Enable/Disable Sourcemaps |
camelCase | {Boolean|String} | false | Export Classnames in CamelCase |
importLoaders | {Number} | 0 | Number of loaders applied before CSS loader |
exportOnlyLocals | {Boolean} | false | Export only locals |
url
Type: Boolean|Function
Default: true
Control url()
resolving. Absolute urls are not resolving.
Examples resolutions:
url(image.png) => require('./image.png')
url('image.png') => require('./image.png')
url(./image.png) => require('./image.png')
url('./image.png') => require('./image.png')
url('http://dontwritehorriblecode.com/2112.png') => require('http://dontwritehorriblecode.com/2112.png')
image-set(url('image2x.png') 1x, url('image1x.png') 2x) => require('./image1x.png') and require('./image2x.png')
To import assets from a node_modules
path (include resolve.modules
) and for alias
, prefix it with a ~
:
url(~module/image.png) => require('module/image.png')
url('~module/image.png') => require('module/image.png')
url(~aliasDirectory/image.png) => require('otherDirectory/image.png')
Boolean
Enable/disable url()
resolving.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
url: true,
},
},
],
},
};
Function
Allow to filter url()
. All filtered url()
will not be resolved (left in the code as they were written).
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
url: (url, resourcePath) => {
// resourcePath - path to css file
// `url()` with `img.png` stay untouched
return url.includes('img.png');
},
},
},
],
},
};
import
Type: Boolean
Default: true
Control @import
resolving. Absolute urls in @import
will be moved in runtime code.
Examples resolutions:
@import 'style.css' => require('./style.css')
@import url(style.css) => require('./style.css')
@import url('style.css') => require('./style.css')
@import './style.css' => require('./style.css')
@import url(./style.css) => require('./style.css')
@import url('./style.css') => require('./style.css')
@import url('http://dontwritehorriblecode.com/style.css') => @import url('http://dontwritehorriblecode.com/style.css') in runtime
To import styles from a node_modules
path (include resolve.modules
) and for alias
, prefix it with a ~
:
@import url(~module/style.css) => require('module/style.css')
@import url('~module/style.css') => require('module/style.css')
@import url(~aliasDirectory/style.css) => require('otherDirectory/style.css')
Boolean
Enable/disable @import
resolving.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
import: true,
},
},
],
},
};
Function
Allow to filter @import
. All filtered @import
will not be resolved (left in the code as they were written).
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
import: (parsedImport, resourcePath) => {
// parsedImport.url - url of `@import`
// parsedImport.media - media query of `@import`
// resourcePath - path to css file
// `@import` with `style.css` stay untouched
return parsedImport.url.includes('style.css');
},
},
},
],
},
};
modules
Type: Boolean|String
Default: false
The modules
option enables/disables the CSS Modules spec and setup basic behaviour.
Name | Type | Description |
---|---|---|
true | {Boolean} | Enables local scoped CSS by default (use local mode by default) |
false | {Boolean} | Disable the CSS Modules spec, all CSS Modules features (like @value , :local , :global and composes ) will not work |
'local' | {String} | Enables local scoped CSS by default (same as true value) |
'global' | {String} | Enables global scoped CSS by default |
Using false
value increase performance because we avoid parsing CSS Modules features, it will be useful for developers who use vanilla css or use other technologies.
You can read about modes below.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
modules: true,
},
},
],
},
};
Scope
Using local
value requires you to specify :global
classes.
Using global
value requires you to specify :local
classes.
You can find more information here.
Styles can be locally scoped to avoid globally scoping styles.
The syntax :local(.className)
can be used to declare className
in the local scope. The local identifiers are exported by the module.
With :local
(without brackets) local mode can be switched on for this selector.
The :global(.className)
nocation can be used to declare an explicit global selector.
With :global
(without brackets) global mode can be switched on for this selector.
The loader replaces local selectors with unique identifiers. The chosen unique identifiers are exported by the module.
:local(.className) {
background: red;
}
:local .className {
color: green;
}
:local(.className .subClass) {
color: green;
}
:local .className .subClass :global(.global-class-name) {
color: blue;
}
._23_aKvs-b8bW2Vg3fwHozO {
background: red;
}
._23_aKvs-b8bW2Vg3fwHozO {
color: green;
}
._23_aKvs-b8bW2Vg3fwHozO ._13LGdX8RMStbBE9w-t0gZ1 {
color: green;
}
._23_aKvs-b8bW2Vg3fwHozO ._13LGdX8RMStbBE9w-t0gZ1 .global-class-name {
color: blue;
}
ℹ️ Identifiers are exported
exports.locals = {
className: '_23_aKvs-b8bW2Vg3fwHozO',
subClass: '_13LGdX8RMStbBE9w-t0gZ1',
};
CamelCase is recommended for local selectors. They are easier to use within the imported JS module.
You can use :local(#someId)
, but this is not recommended. Use classes instead of ids.
Composing
When declaring a local classname you can compose a local class from another local classname.
:local(.className) {
background: red;
color: yellow;
}
:local(.subClass) {
composes: className;
background: blue;
}
This doesn't result in any change to the CSS itself but exports multiple classnames.
exports.locals = {
className: '_23_aKvs-b8bW2Vg3fwHozO',
subClass: '_13LGdX8RMStbBE9w-t0gZ1 _23_aKvs-b8bW2Vg3fwHozO',
};
._23_aKvs-b8bW2Vg3fwHozO {
background: red;
color: yellow;
}
._13LGdX8RMStbBE9w-t0gZ1 {
background: blue;
}
Importing
To import a local classname from another module.
:local(.continueButton) {
composes: button from 'library/button.css';
background: red;
}
:local(.nameEdit) {
composes: edit highlight from './edit.css';
background: red;
}
To import from multiple modules use multiple composes:
rules.
:local(.className) {
composes: edit hightlight from './edit.css';
composes: button from 'module/button.css';
composes: classFromThisModule;
background: red;
}
localIdentName
Type: String
Default: [hash:base64]
You can configure the generated ident with the localIdentName
query parameter.
See loader-utils's documentation for more information on options.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
modules: true,
localIdentName: '[path][name]__[local]--[hash:base64:5]',
},
},
],
},
};
You can also specify the absolute path to your custom getLocalIdent
function to generate classname based on a different schema.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
modules: true,
context: path.resolve(__dirname, 'context'), // Allow to redefine basic loader context for `local-ident-name`
hashPrefix: 'hash', // Allow to add custom hash to generate more unique classes
localIdentName: '[path][name]__[local]--[hash:base64:5]',
getLocalIdent: (context, localIdentName, localName, options) => {
return 'whatever_random_class_name';
},
},
},
],
},
};
sourceMap
Type: Boolean
Default: true
To include source maps set the sourceMap
option.
I.e. the mini-css-extract-plugin
can handle them.
They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS source maps do not). In addition to that relative paths are buggy and you need to use an absolute public path which includes the server URL.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
sourceMap: true,
},
},
],
},
};
camelCase
Type: Boolean|String
Default: false
By default, the exported JSON keys mirror the class names. If you want to camelize class names (useful in JS), pass the query parameter camelCase
to css-loader.
Name | Type | Description |
---|---|---|
false | {Boolean} | Class names will be camelized, the original class name will not to be removed from the locals |
true | {Boolean} | Class names will be camelized |
'dashes' | {String} | Only dashes in class names will be camelized |
'only' | {String} | Introduced in 0.27.1 . Class names will be camelized, the original class name will be removed from the locals |
'dashesOnly' | {String} | Introduced in 0.27.1 . Dashes in class names will be camelized, the original class name will be removed from the locals |
file.css
.class-name {
}
file.js
import { className } from 'file.css';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
camelCase: true,
},
},
],
},
};
importLoaders
Type: Number
Default: 0
The option importLoaders
allows you to configure how many loaders before css-loader
should be applied to @import
ed resources.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: [
'style-loader',
{
loader: 'css-loader',
options: {
importLoaders: 2, // 0 => no loaders (default); 1 => postcss-loader; 2 => postcss-loader, sass-loader
},
},
'postcss-loader',
'sass-loader',
],
},
],
},
};
This may change in the future when the module system (i. e. webpack) supports loader matching by origin.
exportOnlyLocals
Type: Boolean
Default: false
Export only locals (useful when you use css modules).
For pre-rendering with mini-css-extract-plugin
you should use this option instead of style-loader!css-loader
in the pre-rendering bundle.
It doesn't embed CSS but only exports the identifier mappings.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
loader: 'css-loader',
options: {
exportOnlyLocals: true,
},
},
],
},
};
The following webpack.config.js
can load CSS files, embed small PNG/JPG/GIF/SVG images as well as fonts as Data URLs and copy larger files to the output directory.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: ['style-loader', 'css-loader'],
},
{
test: /\.(png|jpg|gif|svg|eot|ttf|woff|woff2)$/,
loader: 'url-loader',
options: {
limit: 10000,
},
},
],
},
};
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.
This can be achieved by using the mini-css-extract-plugin to extract the CSS when running in production mode.
As an alternative, if seeking better development performance and css outputs that mimic production. extract-css-chunks-webpack-plugin offers a hot module reload friendly, extended version of mini-css-extract-plugin. HMR real CSS files in dev, works like mini-css in non-dev
Please take a moment to read our contributing guidelines if you haven't yet done so.
FAQs
css loader module for webpack
The npm package css-loader receives a total of 15,263,079 weekly downloads. As such, css-loader popularity was classified as popular.
We found that css-loader demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
Did you know?
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