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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.
npm install --save-dev css-loader
The css-loader
interprets @import
and url()
like import/require()
and will resolve them.
Good loaders for requiring your assets are the file-loader and the url-loader which you should specify in your config (see below).
file.js
import css from 'file.css';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: [ 'style-loader', 'css-loader' ]
}
]
}
}
toString
You can also use the css-loader results directly as string, such as in Angular's component style.
webpack.config.js
{
test: /\.css$/,
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
{
test: /\.css$/,
use: [
'handlebars-loader', // handlebars loader expects raw resource string
'extract-loader',
'css-loader'
]
}
Name | Type | Default | Description |
---|---|---|---|
url | {Boolean} | true | Enable/Disable url() handling |
import | {Boolean} | true | Enable/Disable @import handling |
modules | {Boolean} | false | Enable/Disable CSS Modules |
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 |
url
To disable url()
resolving by css-loader
set the option to false
.
To be compatible with existing css files (if not in CSS Module mode).
url(image.png) => require('./image.png')
url(~module/image.png) => require('module/image.png')
import
To disable @import
resolving by css-loader
set the option to false
@import url('https://fonts.googleapis.com/css?family=Roboto');
⚠️ Use with caution, since this disables resolving for all
@import
s, including css modulescomposes: xxx from 'path/to/file.css'
feature.
modules
The query parameter modules
enables the CSS Modules spec.
This enables local scoped CSS by default. (You can switch it off with :global(...)
or :global
for selectors and/or rules.).
Scope
By default CSS exports all classnames into a global selector scope. 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. :global(.className)
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 choosen 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 in the within the imported JS module.
url()
URLs in block scoped (:local .abc
) rules behave like requests in modules.
file.png => ./file.png
~module/file.png => module/file.png
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
You can configure the generated ident with the localIdentName
query parameter. See loader-utils's documentation for more information on options.
webpack.config.js
{
test: /\.css$/,
use: [
{
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. This requires webpack >= 2.2.1
(it supports functions in the options
object).
webpack.config.js
{
loader: 'css-loader',
options: {
modules: true,
localIdentName: '[path][name]__[local]--[hash:base64:5]',
getLocalIdent: (context, localIdentName, localName, options) => {
return 'whatever_random_class_name'
}
}
}
ℹ️ For prerendering with extract-text-webpack-plugin you should use
css-loader/locals
instead ofstyle-loader!css-loader
in the prerendering bundle. It doesn't embed CSS but only exports the identifier mappings.
sourceMap
To include source maps set the sourceMap
option.
I. e. the extract-text-webpack-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 include the server URL.
webpack.config.js
{
loader: 'css-loader',
options: {
sourceMap: true
}
}
camelCase
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 |
---|---|---|
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
{
loader: 'css-loader',
options: {
camelCase: true
}
}
importLoaders
The query parameter importLoaders
allows to configure how many loaders before css-loader
should be applied to @import
ed resources.
webpack.config.js
{
test: /\.css$/,
use: [
'style-loader',
{
loader: 'css-loader',
options: {
importLoaders: 2 // 0 => no loaders (default); 1 => postcss-loader; 2 => postcss-loader, sass-loader
}
},
'postcss-loader',
'sass-loader'
]
}
This may change in the future, when the module system (i. e. webpack) supports loader matching by origin.
The following webpack.config.js
can load CSS files, embed small PNG/JPG/GIF/SVG images as well as fonts as Data URLs and copy larger files to the output directory.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
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.
Juho Vepsäläinen |
Joshua Wiens |
Kees Kluskens |
Sean Larkin |
Michael Ciniawsky |
Evilebot Tnawi |
Joscha Feth |
1.0.0 (2018-07-06)
minimize
option, use postcss-loader
with cssnano
or use optimize-cssnano-plugin
pluginmodule
option, use modules
option insteadcamelcase
option, use camelCase
option insteadroot
option, use postcss-loader
with postcss-url
pluginalias
option, use resolve.alias
feature or use postcss-loader
with postcss-url
pluginpostcss
to 6
versionnodejs
version is 6.9
webpack
version is 4
<a name="0.28.11"></a>
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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