webpack 熱更新時 warnings

錯誤

WARNING in configuration
The 'mode' option has not been set. Set 'mode' option to 'development' or 'production' to enable defaults for this environment.

WARNING in asset size limit: The following asset(s) exceed the recommended size limit (244 KiB).
This can impact web performance.
Assets:
  print.0989fjs (348 KiB)
  vendors.0989fjs (357 KiB)
  index.0989fjs (885 KiB)

WARNING in entrypoint size limit: The following entrypoint(s) combined asset size exceeds the recommended limit (244 KiB). This can impact web performance.
Entrypoints:
  index (885 KiB)
      index.0989fjs
  vendors (357 KiB)
      vendors.0989fjs
  print (348 KiB)
      print.0989fjs


WARNING in webpack performance recommendations:
You can limit the size of your bundles by using import() or require.ensure to lazy load some parts of your application.
For more info visit https://webpack.js.org/guides/code-splitting/

這是配置文件

const webpack = require('webpack');

module.exports = {
    // devtool: 'inline-source-map',
    devServer: {
        contentBase: './dist',
        compress:true,
        port:9000,
        host:'127.0.0.1',
        hot: true, 
       
    },
    entry: {
        index: './src/index.js',
        vendors: ['react'],
        
    },

    plugins: [
        new CleanWebpackPlugin(['dist']),
        new HTMLWebpackPlugin({
            title: 'Code Splitting'
        }),
        new webpack.NamedModulesPlugin(),
        new webpack.HotModuleReplacementPlugin()

    
    ],
    
    output: {
        filename: '[name].[hash:5]js',
        path: path.resolve(__dirname, 'dist'),
        hotUpdateChunkFilename: 'hot/hot-update.js',  //指定熱替換補丁js文件和
        hotUpdateMainFilename: 'hot/hot-update.json', //json描述文件生成路徑 ，每次文件變化都會生成一次
    }
};

要如何處理呢