Webpack 3 to Webpack 4

webpack3.config.js

{
  entry: {
    pageA: "path/to/pageA_entry.js",
    pageB: "path/to/pageB_entry.js",
    vendor: "path/to/vendor_entry.js",
  },
      
  //.. other configuration not relevant here  
    
  plugins: [
        new CommonsChunkPlugin({
            name: "shared",
            filename: "shared.js",
            minChunks: 3
        })
    ]
}

webpack4.config.js

{
  entry: {
    pageA: "path/to/pageA_entry.js",
    pageB: "path/to/pageB_entry.js",
    vendor: "path/to/vendor_entry.js",
  },
  
  //.. other configuration not relevant here
  
  optimization: {
        splitChunks: {
            cacheGroups: {
                commons: {
                    name: "commons",
                    chunks: "initial",
                    minChunks: 3
                },
                vendor: {
                    name: "vendor",
                    test: "vendor",
                    priority: 10,
                    enforce: true
                }
            }
        },
        runtimeChunk: "single"
    }
}