extract-css-chunks-webpack-plugin

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extract-css-chunks-webpack-plugin

This plugin extracts CSS into separate files. It creates a CSS file per JS file which contains CSS. It supports On-Demand-Loading of CSS and SourceMaps.

It builds on top of a new webpack v4 feature (module types) and requires webpack 4 to work.

Compared to the extract-text-webpack-plugin:

Async loading
No duplicate compilation (performance)
Easier to use
Specific to CSS

Getting Started

To begin, you'll need to install extract-css-chunks-webpack-plugin:

npm install --save-dev extract-css-chunks-webpack-plugin

It's recommended to combine extract-css-chunks-webpack-plugin with the css-loader

Then add the loader and the plugin to your webpack config. For example:

style.css

body {
  background: green;
}

component.js

import './style.css';

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [new ExtractCssChunks()],
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

Options

`publicPath`

Type: String|Function Default: the publicPath in webpackOptions.output

Specifies a custom public path for the target file(s).

`String`

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: '[name].css',
      chunkFilename: '[id].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              publicPath: '/public/path/to/',
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};

`Function`

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: '[name].css',
      chunkFilename: '[id].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              publicPath: (resourcePath, context) => {
                return path.relative(path.dirname(resourcePath), context) + '/';
              },
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};

`esModule`

Type: Boolean Default: false

By default, extract-css-chunks-webpack-plugin generates JS modules that use the CommonJS 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 ES module syntax using:

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [new ExtractCssChunks()],
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              esModule: true,
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};

Examples

Minimal example

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      // Options similar to the same options in webpackOptions.output
      // all options are optional
      filename: '[name].css',
      chunkFilename: '[id].css',
      ignoreOrder: false, // Enable to remove warnings about conflicting order
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              // you can specify a publicPath here
              // by default it uses publicPath in webpackOptions.output
              publicPath: '../',
              hmr: process.env.NODE_ENV === 'development',
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};

The `publicPath` option as function

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: '[name].css',
      chunkFilename: '[id].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              publicPath: (resourcePath, context) => {
                // publicPath is the relative path of the resource to the context
                // e.g. for ./css/admin/main.css the publicPath will be ../../
                // while for ./css/main.css the publicPath will be ../
                return path.relative(path.dirname(resourcePath), context) + '/';
              },
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};

Advanced configuration example

This plugin should be used only on production builds without style-loader in the loaders chain, especially if you want to have HMR in development.

Here is an example to have both HMR in development and your styles extracted in a file for production builds.

(Loaders options left out for clarity, adapt accordingly to your needs.)

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');
const devMode = process.env.NODE_ENV !== 'production';

module.exports = {
  plugins: [
    new ExtractCssChunks({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: devMode ? '[name].css' : '[name].[hash].css',
      chunkFilename: devMode ? '[id].css' : '[id].[hash].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.(sa|sc|c)ss$/,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              hmr: process.env.NODE_ENV === 'development',
            },
          },
          'css-loader',
          'postcss-loader',
          'sass-loader',
        ],
      },
    ],
  },
};

Hot Module Reloading (HMR)

The extract-css-chunks-webpack-plugin supports hot reloading of actual css files in development. Some options are provided to enable HMR of both standard stylesheets and locally scoped CSS or CSS modules. Below is an example configuration of mini-css for HMR use with CSS modules.

While we attempt to hmr css-modules. It is not easy to perform when code-splitting with custom chunk names. reloadAll is an option that should only be enabled if HMR isn't working correctly. The core challenge with css-modules is that when code-split, the chunk ids can and do end up different compared to the filename.

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: '[name].css',
      chunkFilename: '[id].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          {
            loader: ExtractCssChunks.loader,
            options: {
              // only enable hot in development
              hmr: process.env.NODE_ENV === 'development',
              // if hmr does not work, this is a forceful method.
              reloadAll: true,
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};

Minimizing For Production

To minify the output, use a plugin like optimize-css-assets-webpack-plugin. Setting optimization.minimizer overrides the defaults provided by webpack, so make sure to also specify a JS minimizer:

webpack.config.js

const TerserJSPlugin = require('terser-webpack-plugin');
const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');
const OptimizeCSSAssetsPlugin = require('optimize-css-assets-webpack-plugin');

module.exports = {
  optimization: {
    minimizer: [new TerserJSPlugin({}), new OptimizeCSSAssetsPlugin({})],
  },
  plugins: [
    new ExtractCssChunks({
      filename: '[name].css',
      chunkFilename: '[id].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

Using preloaded or inlined CSS

The runtime code detects already added CSS via <link> or <style> tag. This can be useful when injecting CSS on server-side for Server-Side-Rendering. The href of the <link> tag has to match the URL that will be used for loading the CSS chunk. The data-href attribute can be used for <link> and <style> too. When inlining CSS data-href must be used.

Extracting all CSS in a single file

Similar to what extract-text-webpack-plugin does, the CSS can be extracted in one CSS file using optimization.splitChunks.cacheGroups.

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  optimization: {
    splitChunks: {
      cacheGroups: {
        styles: {
          name: 'styles',
          test: /\.css$/,
          chunks: 'all',
          enforce: true,
        },
      },
    },
  },
  plugins: [
    new ExtractCssChunks({
      filename: '[name].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

Extracting CSS based on entry

You may also extract the CSS based on the webpack entry name. This is especially useful if you import routes dynamically but want to keep your CSS bundled according to entry. This also prevents the CSS duplication issue one had with the ExtractTextPlugin.

const path = require('path');
const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

function recursiveIssuer(m) {
  if (m.issuer) {
    return recursiveIssuer(m.issuer);
  } else if (m.name) {
    return m.name;
  } else {
    return false;
  }
}

module.exports = {
  entry: {
    foo: path.resolve(__dirname, 'src/foo'),
    bar: path.resolve(__dirname, 'src/bar'),
  },
  optimization: {
    splitChunks: {
      cacheGroups: {
        fooStyles: {
          name: 'foo',
          test: (m, c, entry = 'foo') =>
            m.constructor.name === 'CssModule' && recursiveIssuer(m) === entry,
          chunks: 'all',
          enforce: true,
        },
        barStyles: {
          name: 'bar',
          test: (m, c, entry = 'bar') =>
            m.constructor.name === 'CssModule' && recursiveIssuer(m) === entry,
          chunks: 'all',
          enforce: true,
        },
      },
    },
  },
  plugins: [
    new ExtractCssChunks({
      filename: '[name].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

Module Filename Option

With the moduleFilename option you can use chunk data to customize the filename. This is particularly useful when dealing with multiple entry points and wanting to get more control out of the filename for a given entry point/chunk. In the example below, we'll use moduleFilename to output the generated css into a different directory.

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      moduleFilename: ({ name }) => `${name.replace('/js/', '/css/')}.css`,
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

Long Term Caching

For long term caching use filename: "[contenthash].css". Optionally add [name].

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      filename: '[name].[contenthash].css',
      chunkFilename: '[id].[contenthash].css',
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

Remove Order Warnings

For projects where css ordering has been mitigated through consistent use of scoping or naming conventions, the css order warnings can be disabled by setting the ignoreOrder flag to true for the plugin.

webpack.config.js

const ExtractCssChunks = require('extract-css-chunks-webpack-plugin');

module.exports = {
  plugins: [
    new ExtractCssChunks({
      ignoreOrder: true,
    }),
  ],
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [ExtractCssChunks.loader, 'css-loader'],
      },
    ],
  },
};

insert

Type: String|Function Default: head

By default, the mini-css-extract-plugin appends styles (<link> elements) to document.head of the current window.

However in some circumstances it might be necessary to have finer control over the append target or even delay link elements instertion. For example this is the case when you asynchronously load styles for an application that runs inside of an iframe. In such cases insert can be configured to be a function or a custom selector.

If you target an iframe make sure that the parent document has sufficient access rights to reach into the frame document and append elements to it.

`insert` as a string

Allows to configure a CSS selector that will be used to find the element where to append the styles (link elements).

new MiniCssExtractPlugin({
  insert: '#my-container',
});

A new <link> element will be appended to the #my-container element.

`insert` as a function

Allows to override default behavior and insert styles at any position.

⚠ Do not forget that this code will run in the browser alongside your application. Since not all browsers support latest ECMA features like let, const, arrow function expression and etc we recommend you to use only ECMA 5 features and syntax.

⚠ The insert function is serialized to string and passed to the plugin. This means that it won't have access to the scope of the webpack configuration module.

new MiniCssExtractPlugin({
  insert: function insert(linkTag) {
    const reference = document.querySelector('#some-element');
    if (reference) {
      reference.parentNode.insertBefore(linkTag, reference);
    }
  },
});

A new <link> element will be inserted before the element with id some-element.

Media Query Plugin

If you'd like to extract the media queries from the extracted CSS (so mobile users don't need to load desktop or tablet specific CSS anymore) you should use one of the following plugins: