css loader for webpack

installation

npm install css-loader --save-dev

Usage

Documentation: Using loaders

var css = require("css-loader!./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 (if not in CSS Module mode):

• 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" },
      { 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")

Using 'Root-relative' urls is not recommended. You should only use it for legacy CSS files.

Local scope

By default CSS exports all class names 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.

Example:

:local(.className) { background: red; }
:local .className { color: green; }
:local(.className .subClass) { color: green; }
:local .className .subClass :global(.global-class-name) { color: blue; }

is transformed to

._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; }

and the identifiers are exported:

exports.locals = {
  className: "_23_aKvs-b8bW2Vg3fwHozO",
  subClass: "_13LGdX8RMStbBE9w-t0gZ1"
}

Camelcasing is recommended for local selectors. They are easier to use in the importing javascript module.

url(...) URLs in block scoped (:local .abc) rules behave like requests in modules:

• ./file.png instead of file.png
• module/file.png instead of ~module/file.png

You can use :local(#someId), but this is not recommended. Use classes instead of ids.

You can configure the generated ident with the localIdentName query parameter (default [hash:base64]). Example: css-loader?localIdentName=[path][name]---[local]---[hash:base64:5] for easier debugging.

You can also specify the absolute path to your custom getLocalIdent function to generate classname based on a different schema. Note that this requires webpack@2 since to be able to pass function in. For example:

{
    test: /\.css$/,
    loaders: [
        {
            loader: 'css-loader',
            query: {
                modules: true,
                importLoaders: 1,
                getLocalIdent: function (loaderContext, localIdentName, localName, options) {
                  return 'whatever_random_class_name'
                }
            }
        }
    ]
},

Note: For prerendering with extract-text-webpack-plugin you should use css-loader/locals instead of style-loader!css-loader in the prerendering bundle. It doesn't embed CSS but only exports the identifier mappings.

CSS Modules

See CSS Modules.

The query parameter modules enables the CSS Modules spec. (css-loader?modules)

This enables Local scoped CSS by default. (You can switch it off with :global(...) or :global for selectors and/or rules.)

Composing CSS classes

When declaring a local class name you can compose a local class from another local class name.

: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 class names:

exports.locals = {
  className: "_23_aKvs-b8bW2Vg3fwHozO",
  subClass: "_13LGdX8RMStbBE9w-t0gZ1 _23_aKvs-b8bW2Vg3fwHozO"
}

and CSS is transformed to:

._23_aKvs-b8bW2Vg3fwHozO {
  background: red;
  color: yellow;
}

._13LGdX8RMStbBE9w-t0gZ1 {
  background: blue;
}

Importing local class names

To import a local class name 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;
}

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.

They are not enabled by default because they expose a runtime overhead and increase in bundle size (JS SourceMap do not). In addition to that relative paths are buggy and you need to use an absolute public path which include the server url.

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

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

This may change in the future, when the module system (i. e. webpack) supports loader matching by origin.

Minification

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

In some cases the minification is destructive to the css, so you can provide some options to it. cssnano is used for minification and you find a list of options here. Just provide them as query parameter: i. e. require("css-loader?-colormin") to disable making color values as small as possible.

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)

Disable behavior

css-loader?-url disables url(...) handling.

css-loader?-import disables @import handling.

Camel case

By default, the exported JSON keys mirror the class names. If you want to camelize class names (useful in Javascript), pass the query parameter camelCase to the loader.

Example:

css-loader?camelCase

Usage:

/* file.css */

.class-name { /* ... */ }

// javascript

require('file.css').className

License

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