$q promise with Underscore _each

Question

So I have a method in a angularjs server that is calling a method that returns a promise for each method in a array. I am using underscore _each to loop through the array. I

Answer 1

You want to use $q.all, which takes an array of promises. So use map instead of each, and pass the result to $q.all(), which gives you a promise that waits for all of them. You don't even need that stuff array which is manually filled, but just can use the resolution value of that new promise.

function processCoolStuff(coolStuffs) {
    return $q.all(_.map(coolStuffs, makeStuffCooler));
}
processCoolStuff(…).then(showAllMyCoolStuff);

Answer 2

after I read the question and the according answer, I got on the right track. Thanks so far! But for the final working soltion I spent another hour to get all use cases working. That's why I would like to share a code example which contains chained promises including an array of promises to wait for resolution.

Use case background is a server-side (nodeJs) file import after upload. I used promises in order to return an appropriate http status and result.

readFile: function (fileName) {
    if (fileName) {
        var deferred = Q.defer();
        var self = this;
        converter({input: fileName}, function (error, userData) {
            if (error) {
                deferred.reject(error);
            }
            self.storeUsers(error, userData)
                .then(function (success) {
                    if (success) {
                        deferred.resolve(success)
                    }
                })
                .fail(function (error) {                       
                    deferred.reject(error)                      
                });
        });
        return deferred.promise;
    }
},

storeUsers: function (error, data) {
    return Q.all(_.map(data, function (users, emailAddress) {
        var deferred = Q.defer();
        userRepository.findUserByEmail(emailAddress, function (user) {
            //...
            user.save(function (error) {
                if (error) {
                    deferred.reject(error);
                } else {
                    deferred.resolve(emailAddress);
                }
            });

        });
        return deferred.promise;
    }));
}

Hope that helps too!

Cheers Ben

Answer 3

$q.all([promise1,promise2,promise3,etc])
.then(function(results){
   alert("This alert will happen after all promises are resolved.");
 })