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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$/i,
use: ['style-loader', 'css-loader'],
},
],
},
};
Good loaders for requiring your assets are the file-loader and the url-loader which you should specify in your config (see below).
And run webpack
via your preferred method.
toString
You can also use the css-loader results directly as a string, such as in Angular's component style.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
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$/i,
use: [
'handlebars-loader', // handlebars loader expects raw resource string
'extract-loader',
'css-loader',
],
},
],
},
};
Name | Type | Default | Description |
---|---|---|---|
url | {Boolean|Function} | true | Enables/Disables url /image-set functions handling |
import | {Boolean|Function} | true | Enables/Disables @import at-rules handling |
modules | {Boolean|String|Object} | false | Enables/Disables CSS Modules and their configuration |
sourceMap | {Boolean} | false | Enables/Disables generation of source maps |
importLoaders | {Number} | 0 | Enables/Disables or setups number of loaders applied before CSS loader |
localsConvention | {String} | asIs | Style of exported classnames |
onlyLocals | {Boolean} | false | Export only locals |
url
Type: Boolean|Function
Default: true
Enables/Disables url
/image-set
functions handling.
Control url()
resolving. Absolute URLs and root-relative URLs are not resolving.
Examples resolutions:
url(image.png) => require('./image.png')
url('image.png') => require('./image.png')
url(./image.png) => require('./image.png')
url('./image.png') => require('./image.png')
url('http://dontwritehorriblecode.com/2112.png') => require('http://dontwritehorriblecode.com/2112.png')
image-set(url('image2x.png') 1x, url('image1x.png') 2x) => require('./image1x.png') and require('./image2x.png')
To import assets from a node_modules
path (include resolve.modules
) and for alias
, prefix it with a ~
:
url(~module/image.png) => require('module/image.png')
url('~module/image.png') => require('module/image.png')
url(~aliasDirectory/image.png) => require('otherDirectory/image.png')
Boolean
Enable/disable url()
resolving.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
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$/i,
loader: 'css-loader',
options: {
url: (url, resourcePath) => {
// resourcePath - path to css file
// Don't handle `img.png` urls
if (url.includes('img.png')) {
return false;
}
return true;
},
},
},
],
},
};
import
Type: Boolean
Default: true
Enables/Disables @import
at-rules handling.
Control @import
resolving. Absolute urls in @import
will be moved in runtime code.
Examples resolutions:
@import 'style.css' => require('./style.css')
@import url(style.css) => require('./style.css')
@import url('style.css') => require('./style.css')
@import './style.css' => require('./style.css')
@import url(./style.css) => require('./style.css')
@import url('./style.css') => require('./style.css')
@import url('http://dontwritehorriblecode.com/style.css') => @import url('http://dontwritehorriblecode.com/style.css') in runtime
To import styles from a node_modules
path (include resolve.modules
) and for alias
, prefix it with a ~
:
@import url(~module/style.css) => require('module/style.css')
@import url('~module/style.css') => require('module/style.css')
@import url(~aliasDirectory/style.css) => require('otherDirectory/style.css')
Boolean
Enable/disable @import
resolving.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
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$/i,
loader: 'css-loader',
options: {
import: (parsedImport, resourcePath) => {
// parsedImport.url - url of `@import`
// parsedImport.media - media query of `@import`
// resourcePath - path to css file
// Don't handle `style.css` import
if (parsedImport.url.includes('style.css')) {
return false;
}
return true;
},
},
},
],
},
};
modules
Type: Boolean|String|Object
Default: false
Enables/Disables CSS Modules and their configuration.
The modules
option enables/disables the CSS Modules specification and setup basic behaviour.
Using false
value increase performance because we avoid parsing CSS Modules features, it will be useful for developers who use vanilla css or use other technologies.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: true,
},
},
],
},
};
Features
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)
notation 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;
}
Values
You can use @value
to specific values to be reused throughout a document.
We recommend use prefix v-
for values, s-
for selectors and m-
for media at-rules.
@value v-primary: #BF4040;
@value s-black: black-selector;
@value m-large: (min-width: 960px);
.header {
color: v-primary;
padding: 0 10px;
}
.s-black {
color: black;
}
@media m-large {
.header {
padding: 0 20px;
}
}
Boolean
Enable CSS Modules features.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: true,
},
},
],
},
};
String
Enable CSS Modules features and setup mode
.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
// Using `local` value has same effect like using `modules: true`
modules: 'global',
},
},
],
},
};
Object
Enable CSS Modules features and setup options for them.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
mode: 'local',
localIdentName: '[path][name]__[local]--[hash:base64:5]',
context: path.resolve(__dirname, 'src'),
hashPrefix: 'my-custom-hash',
},
},
},
],
},
};
mode
Type: String
Default: local
Setup mode
option. You can omit the value when you want local
mode.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
mode: 'global',
},
},
},
],
},
};
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.
Recommendations:
[path][name]__[local]
for development[hash:base64]
for productionThe [local]
placeholder contains original class.
Note: all reserved (<>:"/\|?*
) and control filesystem characters (excluding characters in the [local]
placeholder) will be converted to -
.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
localIdentName: '[path][name]__[local]--[hash:base64:5]',
},
},
},
],
},
};
context
Type: String
Default: undefined
Allow to redefine basic loader context for local ident name.
By default we use rootContext
of loader.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
context: path.resolve(__dirname, 'context'),
},
},
},
],
},
};
hashPrefix
Type: String
Default: undefined
Allow to add custom hash to generate more unique classes.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
hashPrefix: 'hash',
},
},
},
],
},
};
getLocalIdent
Type: Function
Default: undefined
You can also specify the absolute path to your custom getLocalIdent
function to generate classname based on a different schema.
By default we use built-in function to generate a classname.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
getLocalIdent: (context, localIdentName, localName, options) => {
return 'whatever_random_class_name';
},
},
},
},
],
},
};
localIdentRegExp
Type: String|RegExp
Default: undefined
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
modules: {
localIdentRegExp: /page-(.*)\.css/i,
},
},
},
],
},
};
sourceMap
Type: Boolean
Default: false
Enables/Disables generation of source maps.
To include source maps set the sourceMap
option.
They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS source maps do not).
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
sourceMap: true,
},
},
],
},
};
importLoaders
Type: Number
Default: 0
Enables/Disables or setups number of loaders applied before CSS loader.
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$/i,
use: [
'style-loader',
{
loader: 'css-loader',
options: {
importLoaders: 2,
// 0 => no loaders (default);
// 1 => postcss-loader;
// 2 => postcss-loader, sass-loader
},
},
'postcss-loader',
'sass-loader',
],
},
],
},
};
This may change in the future when the module system (i. e. webpack) supports loader matching by origin.
localsConvention
Type: String
Default: undefined
Style of exported classnames.
By default, the exported JSON keys mirror the class names (i.e asIs
value).
Name | Type | Description |
---|---|---|
'asIs' | {String} | Class names will be exported as is. |
'camelCase' | {String} | Class names will be camelized, the original class name will not to be removed from the locals |
'camelCaseOnly' | {String} | Class names will be camelized, the original class name will be removed from the locals |
'dashes' | {String} | Only dashes in class names will be camelized |
'dashesOnly' | {String} | Dashes in class names will be camelized, the original class name will be removed from the locals |
file.css
.class-name {
}
file.js
import { className } from 'file.css';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: 'css-loader',
options: {
localsConvention: 'camelCase',
},
},
],
},
};
onlyLocals
Type: Boolean
Default: false
Export only locals.
Useful when you use css modules for pre-rendering (for example SSR).
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$/i,
loader: 'css-loader',
options: {
onlyLocals: true,
},
},
],
},
};
The following webpack.config.js
can load CSS files, embed small PNG/JPG/GIF/SVG images as well as fonts as Data URLs and copy larger files to the output directory.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
use: ['style-loader', 'css-loader'],
},
{
test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/,
loader: 'url-loader',
options: {
limit: 8192,
},
},
],
},
};
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.
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