Break out of a Promise "then" chain with errorCallback

Question

-- EDIT --

I encountered a weird thing recently about promises, but I guess it's maybe because it's against the philosophy of promises.

Considering the following code :

// Assuming Auth is just a simple lib doing http requests with promises
Auth.signup()
 .then(succCall, errCall)
 .then(loginSucc, loginErr)

// My callbacks here
function succCall (){
 // OK, send second promise
 console.log('succCall');
 return Auth.login();
}

function errCall(){
 // I do some things here and now
 // I want to break out from here
 console.log('errCall');
}

function loginSucc(){
 // This is the callback of the login method when it went OK
 // I want to enter here ONLY if with go through the succCall
 console.log('loginSucc');
}

function loginErr(){
 // This is the callback of the login method when it went not ok
 // I want to enter here ONLY if with go through the succCall
 console.log('loginErr');
}

Here if something goes wrong in Auth.signup(), this is what show :

• errCall, loginSucc

if i do a $q.reject() in the errCall this is what happens :

• errCall, loginErr

and this is what i want :

• errCall... finish, stop here

Now, the problem is, it goes in errCall when signup goes wrong, that's good, but then it enters loginSucc...

I want to break out of the then chain when any errorCallback (which is errCall or loginErr here) is encountered.

-- EDIT --

I think i was misunderstood by some mean, i want to totally break the chain without check in any other "then" if something went wrong.

As if i was saying : if first then is wrong stop here, if first then ok continue, if second "then" ok continue, if third "then" wrong, stop

// Just like if i did the following but by chainning "then" methods
// My callbacks here
function succCall (){
 // OK, send second promise
 return Auth.login().then(loginSucc, loginErr);
}

My point is, i don't want only one error handler if i have many "then" chained

Answer 1

What is effectively happening is this:

    try {
        try {
            var a = succCall();
        } catch(e1) {
            a = errCall(e1);
        }
        var b = loginSucc(a);
    } catch(e2) {
        b = loginErr(e2);
    }

You can break out of the chain by calling

return $q.reject('Reason Err was called');

in your errCall() function.

EDIT: As OP remarked by calling $q.reject the code will enter the loginErr function. Alternatively you can modify your code like this:

Auth.signup()
.then(function(a) {
    succCall()
    return loginSucc(a).then(null, loginErr);
}, errCall)

You can read more in these two SO question:

1. Break promise chain
2. Break Out of then promises in Angularjs

This also is a helpful read : Flattening Promise Chains