报错信息：

yarn add react@16.2.0 react-dom@16.2.0

entry: './src/app.jsx',

module: {

    rules: [

    {

        test: /\.jsx$/,

        exclude: /(node_modules)/, //exclude:对这里的文件不作处理

        use: {

            loader: 'babel-loader',

            options: {

                presets: ['env','react']

            }

        }

    }

    ]

},.......

src/app.jsx

import React, { Component } from 'react';

import ReactDOM from 'react-dom';

ReactDOM.render(

<h1>Hello, world!</h1>,

document.getElementById('root')

);