Sample config to output multiple HTML files with a single JS bundle for testing multiple React and ReactDOM versions via CDN

webpack.config.js

const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')

module.exports = {
  entry: './src/index.js',
  output: {
    path: path.join(__dirname, 'build'),
    filename: 'app.bundle.js'
  },
  module: {
    rules: [
      {
        test: /\.js$/,
        loader: 'babel-loader',
        options: {
          plugins: [
            'transform-class-properties',
            'transform-object-rest-spread'
          ],
          presets: ['env', 'react']
        },
        exclude: /node_modules/
      },
      {
        test: /\.css$/,
        use: ['style-loader', 'css-loader'],
        exclude: /node_modules/
      }
    ]
  },
  externals: {
    react: 'React',
    'react-dom': 'ReactDOM'
  },
  devtool: 'sourcemap',
  plugins: [
    new HtmlWebpackPlugin({
      template: './src/15/index.html',
      filename: 'react_15.html',
      inject: 'body'
    }),
    new HtmlWebpackPlugin({
      template: './src/16/index.html',
      filename: 'react_16.html',
      inject: 'body'
    }),
    new HtmlWebpackPlugin({
      template: './src/16_3/index.html',
      filename: 'react_16_3.html',
      inject: 'body'
    })
  ]
}