function doRequest(url) {
  return new Promise(function (resolve, reject) {
    request(url, function (error, res, body) {
      if (!error && res.statusCode == 200) {
        resolve(body);
      } else {
        reject(error);
      }
    });
  });
}

// Usage:

async function main() {
  let res = await doRequest(url);
  console.log(res);
}

main();

app.post('/signup', async(req, res) => {
  try {
    const { email, firstName } = req.body
    const user = new User({ email, firstName })
    const ret = await user.save()
    res.json(ret)
  } catch (error) {
    console.log(error)
  }
})

app.post('/signup', async(req, res, next) => {
  async function runAsync () {
    await firstThing()
    await secondThing()
  }

  runAsync()
    .catch(next)
})