JarCasting
css-loader
The css-loader interprets @import and url() like import/require() and will resolve them.
Getting Started
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$/i,
use: [
"handlebars-loader", // handlebars loader expects raw resource string
"extract-loader",
"css-loader",
],
},
],
},
};
Options
| Name | Type | Default | Description |
|---|---|---|---|
url |
{Boolean|Function} |
true |
Enables/Disables url/image-set functions handling |
import |
{Boolean|Function} |
true |
Enables/Disables @import at-rules handling |
modules |
{Boolean|String|Object} |
{auto: true} |
Enables/Disables CSS Modules and their configuration |
sourceMap |
{Boolean} |
compiler.devtool |
Enables/Disables generation of source maps |
importLoaders |
{Number} |
0 |
Enables/Disables or setups number of loaders applied before CSS loader |
esModule |
{Boolean} |
true |
Use ES modules syntax |
url
Type: Boolean|Function Default: true
Enables/Disables url/image-set functions handling. Control url() resolving. Absolute URLs are not resolving.
Examples resolutions:
url(image.png) => require('./image.png')
url('image.png') => require('./image.png')
url(./image.png) => require('./image.png')
url('./image.png') => require('./image.png')
url('http://dontwritehorriblecode.com/2112.png') => require('http://dontwritehorriblecode.com/2112.png')
image-set(url('image2x.png') 1x, url('image1x.png') 2x) => require('./image1x.png') and require('./image2x.png')
To import assets from a node_modules path (include resolve.modules) and for alias, prefix it with a ~:
url(~module/image.png) => require('module/image.png')
url('~module/image.png') => require('module/image.png')
url(~aliasDirectory/image.png) => require('otherDirectory/image.png')
Boolean
Enable/disable url() resolving.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/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$/i,
loader: "css-loader",
options: {
url: (url, resourcePath) => {
// resourcePath - path to css file
// Don't handle `img.png` urls
if (url.includes("img.png")) {
return false;
}
return true;
},
},
},
],
},
};
import
Type: Boolean|Function Default: true
Enables/Disables @import at-rules handling. Control @import resolving. Absolute urls in @import will be moved in runtime code.
Examples resolutions:
@import 'style.css' => require('./style.css')
@import url(style.css) => require('./style.css')
@import url('style.css') => require('./style.css')
@import './style.css' => require('./style.css')
@import url(./style.css) => require('./style.css')
@import url('./style.css') => require('./style.css')
@import url('http://dontwritehorriblecode.com/style.css') => @import url('http://dontwritehorriblecode.com/style.css') in runtime
To import styles from a node_modules path (include resolve.modules) and for alias, prefix it with a ~:
@import url(~module/style.css) => require('module/style.css')
@import url('~module/style.css') => require('module/style.css')
@import url(~aliasDirectory/style.css) => require('otherDirectory/style.css')
Boolean
Enable/disable @import resolving.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/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$/i,
loader: "css-loader",
options: {
import: (url, media, resourcePath) => {
// resourcePath - path to css file
// Don't handle `style.css` import
if (url.includes("style.css")) {
return false;
}
return true;
},
},
},
],
},
};
modules
Type: Boolean|String|Object Default: based on filename, true for all files matching /\.module\.\w+$/i.test(filename) regular expression, more information you can read here
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. Using pure value requires selectors must contain at least one local class or id.
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.
i We strongly recommend that you specify the extension when importing a file, since it is possible to import a file with any extension and it is not known in advance which file to use.
: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: {
compileType: "module",
mode: "local",
auto: true,
exportGlobals: true,
localIdentName: "[path][name]__[local]--[hash:base64:5]",
localIdentContext: path.resolve(__dirname, "src"),
localIdentHashPrefix: "my-custom-hash",
namedExport: true,
exportLocalsConvention: "camelCase",
exportOnlyLocals: false,
},
},
},
],
},
};
compileType
Type: 'module' | 'icss' Default: 'module'
Controls the level of compilation applied to the input styles.
The module handles class and id scoping and @value values. The icss will only compile the low level Interoperable CSS format for declaring :import and :export dependencies between CSS and other languages.
ICSS underpins CSS Module support, and provides a low level syntax for other tools to implement CSS-module variations of their own.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
compileType: "icss",
},
},
},
],
},
};
auto
Type: Boolean|RegExp|Function Default: 'true'
Allows auto enable CSS modules based on filename.
Boolean
Possible values:
true- enable css modules for all files for which/\.module\.\w+$/i.test(filename)return truefalse- disable css modules
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
auto: true,
},
},
},
],
},
};
RegExp
Enable css modules for files based on the filename satisfying your regex check.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
auto: /\.custom-module\.\w+$/i,
},
},
},
],
},
};
Function
Enable css modules for files based on the filename satisfying your filter function check.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
auto: (resourcePath) => resourcePath.endsWith(".custom-module.css"),
},
},
},
],
},
};
mode
Type: String|Function Default: 'local'
Setup mode option. You can omit the value when you want local mode.
String
Possible values - local, global, and pure.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
mode: "global",
},
},
},
],
},
};
Function
Allows set different values for the mode option based on a filename
Possible return values - local, global, and pure.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
// Callback must return "local", "global", or "pure" values
mode: (resourcePath) => {
if (/pure.css$/i.test(resourcePath)) {
return "pure";
}
if (/global.css$/i.test(resourcePath)) {
return "global";
}
return "local";
},
},
},
},
],
},
};
localIdentName
Type: String Default: '[hash:base64]'
Allows to configure the generated local ident name. See loader-utils's documentation for more information on options.
Recommendations:
- use
'[path][name]__[local]'for development - use
'[hash:base64]'for production
The [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$/i,
loader: "css-loader",
options: {
modules: {
localIdentName: "[path][name]__[local]--[hash:base64:5]",
},
},
},
],
},
};
localIdentContext
Type: String Default: compiler.context
Allows to redefine basic loader context for local ident name.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
localIdentContext: path.resolve(__dirname, "src"),
},
},
},
],
},
};
localIdentHashPrefix
Type: String Default: undefined
Allows to add custom hash to generate more unique classes.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
localIdentHashPrefix: "hash",
},
},
},
],
},
};
localIdentRegExp
Type: String|RegExp Default: undefined
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
localIdentRegExp: /page-(.*)\.css/i,
},
},
},
],
},
};
getLocalIdent
Type: Function Default: undefined
Allows to specify a function to generate the classname. By default we use built-in function to generate a classname. If the custom function returns null or undefined, we fallback to the built-in function to generate the classname.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
getLocalIdent: (context, localIdentName, localName, options) => {
return "whatever_random_class_name";
},
},
},
},
],
},
};
namedExport
Type: Boolean Default: false
Enables/disables ES modules named export for locals.
⚠ Names of locals are converted to camelcase, i.e. theexportLocalsConventionoption hascamelCaseOnlyvalue by default.
⚠ It is not allowed to use JavaScript reserved words in css class names.
styles.css
.foo-baz {
color: red;
}
.bar {
color: blue;
}
index.js
import { fooBaz, bar } from "./styles.css";
console.log(fooBaz, bar);
You can enable a ES module named export using:
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
esModule: true,
modules: {
namedExport: true,
},
},
},
],
},
};
exportGlobals
Type: Boolean Default: false
Allow css-loader to export names from global class or id, so you can use that as local name.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
exportGlobals: true,
},
},
},
],
},
};
exportLocalsConvention
Type: String Default: based on the modules.namedExport option value, if true - camelCaseOnly, otherwise asIs
Style of exported class names.
By default, the exported JSON keys mirror the class names (i.e asIs value).
⚠ OnlycamelCaseOnlyvalue allowed if you set thenamedExportvalue totrue.
| Name | Type | Description |
|---|---|---|
'asIs' |
{String} |
Class names will be exported as is. |
'camelCase' |
{String} |
Class names will be camelized, the original class name will not to be removed from the locals |
'camelCaseOnly' |
{String} |
Class names will be camelized, the original class name will be removed from the locals |
'dashes' |
{String} |
Only dashes in class names will be camelized |
'dashesOnly' |
{String} |
Dashes in class names will be camelized, the original class name will be removed from the locals |
file.css
.class-name {
}
file.js
import { className } from "file.css";
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
modules: {
exportLocalsConvention: "camelCase",
},
},
},
],
},
};
exportOnlyLocals
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$/i,
loader: "css-loader",
options: {
modules: {
exportOnlyLocals: true,
},
},
},
],
},
};
sourceMap
Type: Boolean Default: depends on the compiler.devtool value
By default generation of source maps depends on the devtool option. All values enable source map generation except eval and false value.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/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 @imported resources.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
use: [
"style-loader",
{
loader: "css-loader",
options: {
importLoaders: 2,
// 0 => no loaders (default);
// 1 => postcss-loader;
// 2 => postcss-loader, sass-loader
},
},
"postcss-loader",
"sass-loader",
],
},
],
},
};
This may change in the future when the module system (i. e. webpack) supports loader matching by origin.
esModule
Type: Boolean Default: true
By default, css-loader generates JS modules that use the ES modules syntax. There are some cases in which using ES modules is beneficial, like in the case of module concatenation and tree shaking.
You can enable a CommonJS modules syntax using:
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
loader: "css-loader",
options: {
esModule: false,
},
},
],
},
};
Examples
Assets
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$/i,
use: ["style-loader", "css-loader"],
},
{
test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/i,
loader: "url-loader",
options: {
limit: 8192,
},
},
],
},
};
Extract
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
Pure CSS, CSS modules and PostCSS
When you have pure CSS (without CSS modules), CSS modules and PostCSS in your project you can use this setup:
webpack.config.js
module.exports = {
module: {
rules: [
{
// For pure CSS - /\.css$/i,
// For Sass/SCSS - /\.((c|sa|sc)ss)$/i,
// For Less - /\.((c|le)ss)$/i,
test: /\.((c|sa|sc)ss)$/i,
use: [
"style-loader",
{
loader: "css-loader",
options: {
// Run `postcss-loader` on each CSS `@import`, do not forget that `sass-loader` compile non CSS `@import`'s into a single file
// If you need run `sass-loader` and `postcss-loader` on each CSS `@import` please set it to `2`
importLoaders: 1,
// Automatically enable css modules for files satisfying `/\.module\.\w+$/i` RegExp.
modules: { auto: true },
},
},
{
loader: "postcss-loader",
options: { plugins: () => [postcssPresetEnv({ stage: 0 })] },
},
// Can be `less-loader`
{
loader: "sass-loader",
},
],
},
{
test: /\.(png|jpe?g|gif|svg|eot|ttf|woff|woff2)$/i,
loader: "url-loader",
options: {
limit: 8192,
},
},
],
},
};
Resolve unresolved URLs using an alias
index.css
.class {
background: url(/assets/unresolved/img.png);
}
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
use: ["style-loader", "css-loader"],
},
],
},
resolve: {
alias: {
"/assets/unresolved/img.png": path.resolve(
__dirname,
"assets/real-path-to-img/img.png"
),
},
},
};
Separating Interoperable CSS-only and CSS Module features
The following setup is an example of allowing Interoperable CSS features only (such as :import and :export) without using further CSS Module functionality by setting compileType option for all files that do not match *.module.scss naming convention. This is for reference as having ICSS features applied to all files was default css-loader behavior before v4. Meanwhile all files matching *.module.scss are treated as CSS Modules in this example.
An example case is assumed where a project requires canvas drawing variables to be synchronized with CSS - canvas drawing uses the same color (set by color name in JavaScript) as HTML background (set by class name in CSS).
webpack.config.js
module.exports = {
module: {
rules: [
// ...
// --------
// SCSS ALL EXCEPT MODULES
{
test: /\.scss$/,
exclude: /\.module\.scss$/,
use: [
{
loader: 'style-loader'
},
{
loader: 'css-loader',
options: {
importLoaders: 1,
modules: {
compileType: 'icss'
}
}
},
{
loader: 'sass-loader'
},
],
},
// --------
// SCSS MODULES
{
test: /\.module\.scss$/,
use: [
{
loader: 'style-loader'
},
{
loader: 'css-loader',
options: {
importLoaders: 1,
modules: {
compileType: 'module'
}
}
},
{
loader: 'sass-loader'
},
],
},
// --------
// ...
},
};
variables.scss
File treated as ICSS-only.
$colorBackground: red;
:export {
colorBackgroundCanvas: $colorBackground;
}
Component.module.scss
File treated as CSS Module.
@import "variables.scss";
.componentClass {
background-color: $colorBackground;
}
Component.jsx
Using both CSS Module functionality as well as SCSS variables directly in JavaScript.
import svars from "variables.scss";
import styles from "Component.module.scss";
// Render DOM with CSS modules class name
// <div className={styles.componentClass}>
// <canvas ref={mountsCanvas}/>
// </div>
// Somewhere in JavaScript canvas drawing code use the variable directly
// const ctx = mountsCanvas.current.getContext('2d',{alpha: false});
ctx.fillStyle = `${svars.colorBackgroundCanvas}`;
Contributing
Please take a moment to read our contributing guidelines if you haven't yet done so.
