webpack.config.js

const path = require('path');
const CleanWebpackPlugin = require('clean-webpack-plugin');

module.exports = {
  mode: 'production', 
  devtool: 'hidden-source-map',
  entry: {
    index: './src/index.js',
  },

  output: {
    filename: '[name].js',
    path: path.resolve(__dirname, "lib"),
    libraryTarget: 'commonjs2'
  },

  module: {
    rules: [
      // {
      //   test: /\.js$/, 
      //   exclude: /node_modules/, 
      //   loader: 'babel-loader?presets[]=env&presets[]=react' 
      // },
      {
        test: /\.js|jsx$/,
        exclude: /(node_modules)/,
        use: {
          loader: 'babel-loader',
          options: {
            presets: ['react', 'es2015', 'babel-preset-env', 'stage-3'],
            plugins: [["transform-class-properties"]]
          }
        }
      },
      {
        test: /\.css$/, 
        use: ['style-loader','css-loader']
      }
    ]
  },

  plugins: [
    new CleanWebpackPlugin(['lib'])
  ]
}