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(bǔ)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