Ensuring promise resolutions in a chain using Angular JavaScript before delivering a final result

Question

Ensuring promise resolutions in a chain using Angular JavaScript before delivering a final result

I have a scenario in Angular where I am using a chain of promises and I want to ensure that a value is returned at the end of the chain:

this.calculateeventsattended = function(username) {
   var Attendees = Parse.Object.extend("Attendees");
   var User = Parse.Object.extend("User");
   var count_pres = 0
   query1 = new Parse.Query(Attendees);
   query1.equalTo("user_id",username);
   query1.equalTo("presence",true)        

   var promise = query1.count(function(count){
       count_pres = count
   }).then(function(){
       query2 = new Parse.Query(User);
       query2.equalTo("username",username);
       query2.first().then(function(object){
           alert("parse" + count_pres)
           object.set("events_attended",count_pres)
           object.save()
       })
   })
$q.all(promise)
return count_pres
}

However, I am facing issues where the 'promise' chain is not resolved before the return statement is executed. This means that count_pres is being returned before $q.all(promise) has finished execution. Any suggestions on how to address this?

javascript angularjs promise

Answer 1

Answer №1

It seems doubtful that this approach will be successful. The comparison between chaining promises and writing asynchronous promises is an interesting one.

function chainedPromises() {
    return $q(function(resolve) {
        query
            .firstPromise()
            .then(function(firstResult) {
                return query.secondPromise(firstResult.something);
            })
            .then(function(secondResult) {
                return query.thirdPromise(secondResult.something);
            })
            .then(function(thirdResult) {
                return query.fourthPromise(thirdResult.something);
            })
            .then(function(fourthResult) {
                resolve(fourthResult);
            });
    });
}

function asyncPromises() {
    var promises = [];

    promises.push(query.firstPromise());
    promises.push(query.secondPromise());
    promises.push(query.thirdPromise());
    promises.push(query.fourthPromise());

    return $q.all(promises);
}

chainedPromises()
    .then(function(fourthResult) {
        doSomethingWith(fourthResult);
    });

asyncPromises()
    .then(function(results) {
       doSomethingWith(results); 
    });

Answer 2

It seems doubtful that this approach will be successful. The comparison between chaining promises and writing asynchronous promises is an interesting one.

function chainedPromises() {
    return $q(function(resolve) {
        query
            .firstPromise()
            .then(function(firstResult) {
                return query.secondPromise(firstResult.something);
            })
            .then(function(secondResult) {
                return query.thirdPromise(secondResult.something);
            })
            .then(function(thirdResult) {
                return query.fourthPromise(thirdResult.something);
            })
            .then(function(fourthResult) {
                resolve(fourthResult);
            });
    });
}

function asyncPromises() {
    var promises = [];

    promises.push(query.firstPromise());
    promises.push(query.secondPromise());
    promises.push(query.thirdPromise());
    promises.push(query.fourthPromise());

    return $q.all(promises);
}

chainedPromises()
    .then(function(fourthResult) {
        doSomethingWith(fourthResult);
    });

asyncPromises()
    .then(function(results) {
       doSomethingWith(results); 
    });

Ensuring promise resolutions in a chain using Angular JavaScript before delivering a final result

Answer №1

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