Webpack 4 WebWorker `window is n

globalObject: 'this',
https://github.com/webpack/webpack/issues/6642

module.exports = {
  entry: ['./src/index', './src/vendor'],
  output: {
    path: path.resolve('./build'),
    filename: '[name].js',
    publicPath: './',
    globalObject: 'this',
  },