webpack.config.js

const path = require('path')
const CleanWebpackPlugin = require('clean-webpack-plugin')
const ExtractTextPlugin = require('extract-text-webpack-plugin')
const StyleLintPlugin = require('stylelint-webpack-plugin')

const plugin = new ExtractTextPlugin({ filename: '[name].css' })
module.exports = {
  entry: './src/index.js',
  output: {
    path: path.resolve(__dirname, 'build'),
    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: [
      {
        enforce: 'pre',
        test: /\.js$/,
        exclude: /node_modules/,
        loader: 'eslint-loader'
      },
      {
        test: /\.js$/,
        include: path.resolve(__dirname, 'src'),
        exclude: /(node_modules|bower_components|build)/,
        use: {
          loader: 'babel-loader',
          options: {
            presets: ['env']
          }
        }
      },
      {
        test: /\.scss$/,
        use: plugin.extract({
          // use, fallback: 'style-loader',
          use: [
            {
              loader: 'css-loader',
              options: {
                importLoaders: 3
              }
            }, {
              loader: 'postcss-loader',
              options: {
                plugins: () => ([require('autoprefixer')()])
              }
            }, {
              loader: 'sass-loader'
            }
          ],
          fallback: 'style-loader'
        })
      }
    ]
  },
  plugins: [
    new CleanWebpackPlugin(path.resolve(__dirname, 'build')),
    plugin,
    new StyleLintPlugin({
      configFile: '.stylelintrc',
      context: './src/assets/styles',
      files: '**/*.scss',
      failOnError: false,
      quiet: false
    })
  ],
  externals: {
    react: 'commonjs react' // this line is just to use the React dependency of our parent-testing-project instead of using our own React.
  }
}