webpack.config.js

module.exports = {
  // Enable sourcemaps for debugging webpack's output.
  devtool: 'source-map',

  resolve: {
    // Add '.ts' and '.tsx' as resolvable extensions.
    extensions: ['.ts', '.tsx'],
  },

  module: {
    rules: [
      {
        test: /\.ts(x?)$/,
        exclude: /node_modules/,
        use: [{ loader: 'ts-loader' }],
      },
      // All output '.js' files will have any sourcemaps re-processed by 'source-map-loader'.
      {
        enforce: 'pre',
        test: /\.js$/,
        loader: 'source-map-loader',
      },
    ],
  },

  // When importing a module whose path matches one of the following, just
  // assume a corresponding global variable exists and use that instead.
  // This is important because it allows us to avoid bundling all of our
  // dependencies, which allows browsers to cache those libraries between builds.
  externals: {
    react: 'React',
    'react-dom': 'ReactDOM',
  },
};