Manage async operations in a sequential flow with bluebird

Question

First off, I am not gonna deny that I am very new to promises and trying to get better at managing promises in my new Node.js app. I am using bluebird based on what I heard from friends and community. Here is a scenario:

The app has a sign up flow, a typical use case where in the following events have to occur in order to sign up a new user:

1. Check if a user already exists.
2. If not, add a new user.
3. Send a verification email.

I do have 3 separate functions addressing each of the above steps.

Now here is what I have come up with using promises flow...but somehow am not convinced with the code below:

user.isExistingUser(email)
        .then((successData) => {
            if(successData && successData.length === 0) {
                user.signUp(signUpInfo)
                .then((successData) => {
                    emailService.sendVerificationEmail(recipientInfo)
                    .then((successData) => {
                     res.json(responseUtility.getApiResponse(successData));
                    })
                    .catch((errorObj) => {
                        res.json(responseUtility.getApiResponse(null, null, errorObj));
                    });
                })
                .catch((errorObj) => {
                    res.json(responseUtility.getApiResponse(null, null, errorObj));
                });
            } else {
                res.json(responseUtility.getApiResponse(null, [{
                    param: 'email',
                    msg: 'An account already exists with this email'
                }], null));
            }
        })
        .catch((errorObj) => {
            res.json(responseUtility.getApiResponse(null, null, errorObj));
        });

As you may see the code seems a bit too long and can become a bit tricky to track. Can some bluebird expert here help with with a better or more readable code?

Answer 1

You should make better use of chaining. Always return promises from your functions that do something asynchronous.

user.isExistingUser(email).then(successData => {
    if (successData && successData.length === 0) {
        return user.signUp(signUpInfo).then(() => {
//      ^^^^^^
            return emailService.sendVerificationEmail(recipientInfo);
//          ^^^^^^
        }).then(successData => {
            res.json(responseUtility.getApiResponse(successData));
        });
    } else {
        res.json(responseUtility.getApiResponse(null, [{
            param: 'email',
            msg: 'An account already exists with this email'
        }], null));
    }
}).catch(errorObj => {
    res.json(responseUtility.getApiResponse(null, null, errorObj));
});