webpack.common.js

const path = require('path');
const ExtractTextPlugin = require("extract-text-webpack-plugin");

const extractLess = new ExtractTextPlugin({
  filename: "styles.css",
  disable: process.env.NODE_ENV === "development"
});

module.exports = {
  entry: ['./dist/index.js'],
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'index.js',
    libraryTarget: 'commonjs2' // THIS IS THE MOST IMPORTANT LINE! :mindblow: I wasted more than 2 days until realize this was the line most important in all this guide.
  },
  module: {
    rules: [
      {
        test: /\.js$/,
        include: path.resolve(__dirname, 'dist'),
        exclude: /(node_modules|bower_components|build)/,
        use: {
          loader: 'babel-loader'
        }
      },
      {
        test: /\.less$|\.css$/,
        use: extractLess.extract({
          use: [{
            loader: "css-loader",
            options: {
              minimize: true
            }
          }, {
            loader: "less-loader"
          }],
          // use style-loader in development
          fallback: "style-loader"
        })
      }
    ]
  },
  externals: {
    'react': 'commonjs react' // this line is just to use the React dependency of our parent-testing-project instead of using our own React.
  },
  plugins: [
    extractLess
  ]
};