css-loader

What is css-loader?

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.

What are css-loader's main functionalities?

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'] }] } };

Other packages similar to css-loader

style-loader

Injects CSS into the DOM using multiple <style> tags. It is often used in conjunction with css-loader.

sass-loader

Loads and compiles Sass/SCSS files. It extends css-loader's functionality to work with Sass/SCSS syntax.

less-loader

Processes Less files and compiles them to CSS. Similar to sass-loader, it's specific to Less preprocessor language.

postcss-loader

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.

mini-css-extract-plugin

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.

README

css loader for webpack

installation

npm install css-loader

Usage

Documentation: Using loaders

var css = require("css!./file.css");
// => returns css code from file.css, resolves imports and url(...)

@import and url(...) are interpreted like require() and will be resolved by the 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).

To be compatible with existing css files:

• url(image.png) => require("./image.png")
• url(~module/image.png) => require("module/image.png")

Example config

This webpack config can load css files, embed small png images as Data Urls and jpg images as files.

module.exports = {
  module: {
    loaders: [
      { test: /\.css$/, loader: "style-loader!css-loader" },
      { test: /\.png$/, loader: "url-loader?limit=100000&mimetype=image/png" },
      { test: /\.jpg$/, loader: "file-loader" }
    ]
  }
};

'Root-relative' urls

For urls that start with a /, the default behavior is to not translate them:

• url(/image.png) => url(/image.png)

If a root query parameter is set, however, it will be prepended to the url and then translated:

With a config like:

    loaders: [
      { test: /\.css$/, loader: "style-loader!css-loader?root=." },
      ...
    ]

The result is:

• url(/image.png) => require("./image.png")

SourceMaps

To include SourceMaps set the sourceMap query param.

require("css-loader?sourceMap!./file.css")

I. e. the extract-text-webpack-plugin can handle them.

importing and chained loaders

The query parameter importLoaders allow to configure which loaders should be applied to @imported resources.

importLoaders (int): That many loaders after the css-loader are used to import resources.

Examples:

require("style-loader!css-loader?importLoaders=1!autoprefixer-loader!...")
// => imported resources are handled this way:
require("css-loader?importLoaders=1!autoprefixer-loader!...")

require("style-loader!css-loader!stylus-loader!...")
// => imported resources are handled this way:
require("css-loader!...")

Minification

By default the css-loader minimizes the css if specified by the module system.

In some cases the structural minification is destructive to the css, so you can disable it with the disableStructuralMinification query parameter. require("css-loader?disableStructuralMinification!./file.css")

You can also disable or enforce minification with the minimize query parameter.

require("css-loader?minimize!./file.css") (enforced)

require("css-loader?-minimize!./file.css") (disabled)

You cannot use minimize with SourceMaps.

License

MIT (http://www.opensource.org/licenses/mit-license.php)