text: const express = require('express');
  const app = express();
  
  app.get('/', (req, res) => {
    res.status(200).send('Hello, world!');
  });
  
  app.get('/users/:username', (req, res) => res.status(200).send(`Hello user ${req.params.username}!`));
  
  
  if (module === require.main) {
    const server = app.listen(process.env.PORT || 8080, () => {
      const port = server.address().port;
    });
  }
  // Must export the Express instance to work correctly on Google App Engine 
  module.exports = app;
  