code: function extractHelperFilesFromCompilation (mainCompilation, childCompilation, filename, childEntryChunks) {
    const helperAssetNames = childEntryChunks.map((entryChunk, index) => {
      return mainCompilation.mainTemplate.hooks.assetPath.call(filename, {
        hash: childCompilation.hash,
        chunk: entryChunk,
        name: `HtmlWebpackPlugin_${index}`
      });
    });
  
    helperAssetNames.forEach((helperFileName) => {
      delete mainCompilation.assets[helperFileName];
    });
  
    const helperContents = helperAssetNames.map((helperFileName) => {
      return childCompilation.assets[helperFileName].source();
    });
  
    return helperContents;
  }
docs: The webpack child compilation will create files as a side effect.
  This function will extract them and clean them up so they won't be written to disk.
  
  Returns the source code of the compiled templates as string
  
  @returns Array<string>