UglifyJsPlugin

 new UglifyJsPlugin({
     uglifyOptions: {
          compress: {
                       warnings: false,
                       drop_debugger: true, // 清除debugger語句
                        drop_console: true,
                        pure_funcs: ['console.log'] // 清除console
                    }
                },
          sourceMap: config.build.productionSourceMap,
          parallel: true,
          cache: true
 })