Node.js：如何在不获取UnhandledPromiseRejectionWarning的情况下返回拒绝的承诺

Question

I have a function in a module that uses the request-promise-native module to query a couchdb database:

userByEmail: (email) => {
  const options = {
    url: `${config.couchdb.url}/medlog/_design/user/_view/by_email_or_userid?key="${email}"`,
    json: true,
  };

  return rp.get(options)
    .then(users => users.rows.map(row => row.value))
    .catch(reason => Promise.reject(new Error('test')));
}

A second module contains a function that uses the first one:

router.get('/checkEmailExistence', (req, res) => {
  couchdb.userByEmail(req.param('email'))
    .then((userArray) => {
      res.status(200).end(userArray.length > 0); // returns 'true' if at least one user found
    })
    .catch((e) => {
      winston.log('error', e.message);
      res.status(500).end(e.message);
});

In the case that there is no database connection, the promise from the request-promise-native module is rejected. What I want is to catch that rejection in the second function and return an internal server error to the caller. To forward the rejection from the request-promise-native module I catch it in the first function and return a new rejected promise.

Unfortunately I always get the warning that I have an unhandled promise rejection. How can I solve that issue?

---

EDIT

I've just seen that I used the wrong codepath for testing. So the coding above works without producing the warning. Sorry for the confusion.

Answer 1

This happen because a Promise always has to return something.

You can fix this 'issue' with a return null

router.get('/checkEmailExistence', (req, res) => {
  couchdb.userByEmail(req.param('email'))
  .then((userArray) => {
    res.status(200).end(userArray.length > 0); // returns 'true' if at least one user found
    return null
  })
  .catch((e) => {
    winston.log('error', e.message);
    res.status(500).end(e.message);
    return null
  });
});