A Webpack plugin that removes duplicate css rules from chunks leaving them only in the parent css asset
Last updated 2 years ago by egorvoronov .
MIT · Repository · Bugs · Original npm · Tarball · package.json
$ cnpm install dedupe-parent-css-from-chunks-webpack-plugin 
SYNC missed versions from official npm registry.

Dedupe parent css from chunks webpack plugin

A Webpack plugin that removes duplicate css rules from chunks leaving them only in the parent css asset.

Many thanks

Inititially, I thought that such kind of optimization could be part of amazing Nuno's Rodrigues NMFR/optimize-css-assets-webpack-plugin, but just to have flies and meatball separately I just created the fork and did the job here. It could be that when you start working with that plugin such feature is already implemented in optimize-css-assets-webpack-plugin, so check that first before download that one (see [] for the details)

What does the plugin do?

It will find all the parents for every chunk, will compare the css rules and will remove the duplicates from chunks only leaving the original rules only inside parent chunks (it uses postcss and postcss-discard-duplicates for processing the assets).

Solves extract-css-chunks-webpack-plugin CSS duplication in chunks problem:

Since extract-css-chunks-webpack-plugin creates separate css chunk for every your splitted js chunk it turns out that your css chunk could contain the rule that are already in the parent asset.


Using npm:

$ npm install --save-dev dedupe-parent-css-from-chunks-webpack-plugin

:warning: This works only for webpack v3 or below. PRs are welcome for webpack v4 and above.


The plugin can receive the following options (all of them are optional):

  • assetNameRegExp: A regular expression that indicates the names of the assets that should be optimized \ minimized. The regular expression provided is run against the filenames of the files exported by the ExtractTextPlugin instances in your configuration, not the filenames of your source CSS files. Defaults to /\.css$/g
  • baseFileRegExp: A regular expression that indicates the base filename and all the chunks would be compared with that file and duplicatest in base file and chunk would be kept only in base file and would be removed from the compared chunk. Default is null
  • duplicationRules: An array of rules that would be applied for deduplication process
    • rule: is an array of regexps. First regexp is considered as a base filename where all the duplications would be moved from other regexp filenames. See the example belof for the details.
  • map: An object that would be passed as postcss processor option, defaults is undefined
  • canPrint: A boolean indicating if the plugin can print messages to the console, defaults to true


const ExtractCssChunks = require("extract-css-chunks-webpack-plugin");
const DedupeParentCssFromChunksWebpackPlugin = require('dedupe-parent-css-from-chunks-webpack-plugin');

module.exports = {
  module: {
    rules: [
        test: /\.css$/,
        loader: ExtractCssChunks.extract('style-loader', 'css-loader')
  plugins: [
    new ExtractCssChunks('styles.css'),
    new DedupeParentCssFromChunksWebpackPlugin({
      assetNameRegExp: /\.optimize\.css$/g, // the default is /\.css$/g
      baseFileRegExp: /\/app\..*?\.?css$/g,  // the default is null
      rules: [
        * This would be the algorithm for rules parsing
        * 1. concat the files together
        * 2. save as original file
        * 3. do the deduplication
        * 4. save as output
        * 5. compare original file with the output - get the diff
        * 6. put the diff into the destination file
        * 7. remove the duplication in destination file if exist
        * 8. remove the duplication in duplication files
            destination: /\/app\..*?\.?css$/g,
            duplications: [ /\/MiniPDPInterstitial\..*?\.?css$/g, /\/ErrorFullPage\..*?\.?css$/g ],
      map: { prev: ... } // the default is undefined
      canPrint: true // the default is true



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  • 2.0.0                                ...           latest (2 years ago)

5 Versions

  • 2.0.0                                ...           2 years ago
  • 1.0.1                                ...           3 years ago
  • 1.0.0                                ...           3 years ago
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  • 0.0.9                                ...           3 years ago
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