How to abort a failing Q promise in Node.JS

Question

Let's say I'm building a registration flow, and I have something that looks like this:

Q.nfcall(validateNewRegCallback, email, password)
    .fail(function(err){
        console.log("bad email/pass: " + err);
        return null;
    })
    .then(function(){
        console.log("Validated!");
    })
    .done();

If my registration fails, I'd like to catch it, and die. Instead, I see both "bad email/pass" and "validated". Why is that, and how can I abort in the first failure call?

Use `promise.catch(onRehected)` method. – Roman Liutikov Feb 17 '14 at 08:14 — Roman Liutikov, Feb 17 '14 at 08:14

score 4 · Accepted Answer · answered Feb 17 '14 at 11:48

The fail handler does catch rejected promises, but then does return a fulfilled promise (with null in your case), as the error was handled already…

So what can you do against this?

Re-throw the error to reject the returned promise. It will cause the done to throw it.

Q.nfcall(validateNewRegCallback, email, password).fail(function(err){
    console.log("bad email/pass: " + err);
    throw err;
}).then(function(){
    console.log("Validated!");
}).done();

Handle the error after the success callback (which also handles errors in the success callback):

Q.nfcall(validateNewRegCallback, email, password).then(function(){
    console.log("Validated!");
}).fail(function(err){
    console.log("bad email/pass: " + err);
}).done();

Simply handle both cases on the same promise - every method does accept two callbacks:

Q.nfcall(validateNewRegCallback, email, password).done(function(){
    console.log("Validated!");
}, function(err){
    console.log("bad email/pass: " + err);
};

You also might use .then(…, …).done() of course.

How to abort a failing Q promise in Node.JS

1 Answers1

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