webpack.config.js

const path = require("path");

module.exports = {
  mode: process.env.NODE_ENV === "production" ? "production" : "development",
  entry: path.resolve(__dirname, "src/index.js"),
  output: {
    path: path.resolve(__dirname, 'lib'),
    filename: "react-optimize.js",
    library: "react-optimize",
    libraryTarget: 'umd',
    umdNamedDefine: true
  },
  externals: {
    react: 'react',
    "prop-types": "prop-types"
  },
  module: {
    rules: [
      {
        test: /\.m?js$/,
        exclude: /(node_modules|bower_components)/,
        use: {
          loader: "babel-loader",
          options: {
            presets: ["@babel/preset-env", "@babel/preset-react"],
            plugins: ["@babel/plugin-proposal-class-properties"]
          }
        }
      }
    ]
  }
};