fast css loader for webpack

This is a fork of the 0.14.5 version of css-loader. We have this fork because 0.15.0+ makes webpack slow

installation

npm install css-loader --save-dev

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" },
      { 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")

Local scope

By default CSS exports all class names into a global selector scope. This is a feature which offer a local selector scope.

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.

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.

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.

Module mode

(experimental)

The query parameter module enables CSS Module mode. (css-loader?module)

• Local scoped by default.
• url(...) URLs behave like requests in modules:
  • ./file.png instead of file.png
  • module/file.png instead of ~module/file.png

Thanks to @markdalgleish for prior work on this topic.

Inheriting

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

:local(.className) {
  background: red;
  color: yellow;
}

:local(.subClass) {
  extends: 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) {
  extends: button from "library/button.css";
  background: red;
}

:local(.nameEdit) {
  extends: edit highlight from "./edit.css";
  background: red;
}

To import from multiple modules use multiple extends: rules. You can also use url(...) to specify the module (it behave a bit different).

:local(.className) {
  extends: edit hightlight from "./edit.css";
  extends: button from url("button.css");
  /* equal to 'extends: button from "./button.css";' */
  extends: 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.

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 minification is destructive to the css, so you can provide some options to it. clean-css is used for minification and you find a list of options here. Just provide them as query parameter: i. e. require("css-loader?-restructuring&compatibility") to disable restructuring and enable compatibility mode.

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)

License

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