Client-side Webpack configuration for development

Update the config object with the following in your webpack.config.client.js file, to configure Webpack for bundling and hot loading React code during development. 

mern-simplesetup/webpack.config.client.js:

const config = {
    name: "browser",
    mode: "development",
    devtool: 'eval-source-map',
    entry: [
        'react-hot-loader/patch',
        'webpack-hot-middleware/client?reload=true',
        path.join(CURRENT_WORKING_DIR, 'client/main.js')
    ],
    output: {
        path: path.join(CURRENT_WORKING_DIR , '/dist'),
        filename: 'bundle.js',
        publicPath: '/dist/'
    },
    module: {
        rules: [
            {
                test: /\.jsx?$/,
                exclude: /node_modules/,
                use: [
                    'babel-loader'
                ]
            }
        ]
    }, plugins: [
          new webpack.HotModuleReplacementPlugin(),
          new webpack.NoEmitOnErrorsPlugin()
      ]
}

• mode sets process.env.NODE_ENV to the given value and tells Webpack to use its built-in optimizations accordingly. If not explicitly set, it defaults to the value 'production'. It can also be set via the command line by passing the value as a CLI argument.
• devtool specifies how source maps are generated, if at all. Generally, a source map provides a way of mapping code within a compressed file back to its original position in a source file to aid debugging.
• entry specifies the entry file where Webpack starts bundling, in this case with the main.js file in the client folder. 
• output specifies the output path for the bundled code, in this case, set to dist/bundle.js.
• publicPath allows specifying the base path for all assets in the application.
• module sets the regex rule for the file extension to be used for transpilation, and the folders to be excluded. The transpilation tool to be used here is babel-loader.
• HotModuleReplacementPlugin enables hot module replacement for react-hot-loader.
• NoEmitOnErrorsPlugin allows skipping emitting when there are compile errors.