How to resolve $q.all?

Question

I have 2 functions, both returning promises:

    var getToken = function() {

        var tokenDeferred = $q.defer();         
        socket.on('token', function(token) {
            tokenDeferred.resolve(token);
        });
        //return promise
        return tokenDeferred.promise;
    }

    var getUserId = function() {
        var userIdDeferred = $q.defer();
        userIdDeferred.resolve('someid');           
        return userIdDeferred.promise;
    }

Now I have a list of topics that I would like to update as soon as these two promises get resolved

    var topics = {      
        firstTopic: 'myApp.firstTopic.',  
        secondTopic: 'myApp.secondTopic.',
        thirdTopic: 'myApp.thirdTopic.',
        fourthTopic: 'myApp.fourthTopic.',
    };

Resolved topics should look like this myApp.firstTopic.someid.sometoken

var resolveTopics = function() {
    $q.all([getToken(), getUserId()])
    .then(function(){

        //How can I resolve these topics in here?

    });
}

Solution

$q.all creates a promise that is automatically resolved when all of the promises you pass it are resolved or rejected when any of the promises are rejected.

If you pass it an array like you do then the function to handle a successful resolution will receive an array with each item being the resolution for the promise of the same index, e.g.:

  var resolveTopics = function() {
    $q.all([getToken(), getUserId()])
    .then(function(resolutions){
      var token  = resolutions[0];
      var userId = resolutions[1];
    });
  }

I personally think it is more readable to pass all an object so that you get an object in your handler where the values are the resolutions for the corresponding promise, e.g.:

  var resolveTopics = function() {
    $q.all({token: getToken(), userId: getUserId()})
    .then(function(resolutions){
      var token  = resolutions.token;
      var userId = resolutions.userId;
    });
  }