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jokkydeMacBook-Pro:~ jokky$ cd myreact
jokkydeMacBook-Pro:myreact jokky$ webpack --mode=production
Hash: 57ae446f70b9dac68be7
Version: webpack 4.16.5
Time: 75ms
Built at: 2018/08/09 上午10:54:25
 1 asset
Entrypoint main = main.js
[0] ./src/index.js 223 bytes {0} [built] [failed] [1 error]
ERROR in ./src/index.js 5:2
Module parse failed: Unexpected token (5:2)
You may need an appropriate loader to handle this file type.
| 
| ReactDOM.render(
>   <h1>Hello World!</h1>,
|   document.getElementById('example')
| );

webpack.config.js   

var debug = process.env.NODE_ENV !== "production";
var webpack = require('webpack');
var path = require('path');
module.exports = {
  context: path.join(__dirname),
  devtool: debug ? "inline-sourcemap" : null,
  entry: "./src/js/index.js",
  module: {
    loaders: [
      {
        test: /\.js?$/,
        exclude: /(node_modules)/,
        loader: 'babel-loader',
        query: {
          presets: ['react', 'es2015']
        }
      }
    ]
  },
  output: {
    path: __dirname,
    filename: "./src/bundle.js"
  },
  resolve: {
  extensions: ['', '.js', '.jsx']
},
  plugins: debug ? [] : [
    new webpack.optimize.DedupePlugin(),
    new webpack.optimize.OccurenceOrderPlugin(),
    new webpack.optimize.UglifyJsPlugin({ mangle: false, sourcemap: false }),
  ],
};

page.json

{
  "name": "myreact",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@babel/core": "^7.0.0-beta.56",
    "@babel/preset-react": "^7.0.0-beta.56",
    "babel-loader": "^8.0.0-beta.4",
    "webpack": "^4.16.5",
    "webpack-cli": "^3.1.0",
    "webpack-dev-server": "^3.1.5"
  }
}