Promisify Run Server, Close Server

server.js

// closeServer needs access to a server object, but that only
// gets created when `runServer` runs, so we declare `server` here
// and then assign a value to it in run
let server = http.createServer(app)
  .on('listening', () => {
    console.info(`Your app is listening on port ${server.address().port}`);
  })
  .on('close', () => {
    console.info('server closed');
  })
  .on('error', (err) => {
    console.error(err);
    mongoose.disconnect();
  });

// this function connects to our database, then starts the server
function runServer(databaseUrl = DATABASE_URL, port = PORT) {
  return new Promise((resolve, reject) => {
    mongoose.connect(databaseUrl)
      .then(() => {
        server.listen(port, resolve).on('error', reject);
      })
      .catch(reject);
  });
}

// this function closes the server, and returns a promise. we'll
// use it in our integration tests later.
function closeServer() {
  return mongoose.disconnect()
  .then(() => {
    return new Promise((resolve, reject) => {
      server.close(err => {
        if (err) {return reject(err);}
        resolve();
      });
    });
  });
}

// if server.js is called directly (aka, with `node server.js`), this block
// runs. but we also export the runServer command so other code (for instance, test code) can start the server as needed.
if (require.main === module) {
  runServer().catch(err => console.error(err.message));
}

module.exports = { runServer, app, closeServer };