code: function client(req, res) {
    const compiler = webpack(config);
    compiler.outputFileSystem = fsys;
  
    compiler.run((err, stats) => {
      const file = fsys.readFileSync(path.join(__dirname, 'dist', 'client.js'));
  
      res.setHeader('Content-Length', file.length);
      res.writeHead(200, { 'Content-Type': 'text/javascript' });
  
      res.end(file);
    });
  }
docs: Serve the index.js client bundle.
  
  @param {Request} req HTTP request.
  @param {Response} res HTTP response.
  @private