Returning the output of a promise

Question

I am trying to return the output of a promise. However, I am just getting the actual promise, instead of the value.

What am I doing wrong?

Here's my code:

$rootScope.distance = function(lon1, lat1) {

    var deferred = $q.defer();

    $cordovaGeolocation.getCurrentPosition()
        .then(function (position) {
            deferred.resolve(position);
        }, function(err) {

        });
    return deferred.promise;


}

...and the result

enter image description here

I'm not sure what you're aiming for but that's what I would expect... you need to call `then` on the returned promise. When it's resolved your `then` callback will be invoked with the data you need (`position` in this case). If your code is as you've shown you don't need to bother with the `deferred` stuff as you can just return the promise returned by `$cordovaGeolocation.getCurrentPosition` directly. — James Allardice, Sep 10 '14 at 12:37
You can't get rid of the `then`. Promises do not magically make asynchronous code synchronous. You return a promise, *then* do something with the value it resolves to. — James Allardice, Sep 10 '14 at 12:38
That is why I am trying to use `$q` to return the value when it's resolved — Patrick Reck, Sep 10 '14 at 12:41
@PatrickReck - You can't return the value when it's resolved. It has nowhere to return to. What you can do (and what you *are* doing) is return a promise for that value and do something with it when it's resolved. — James Allardice, Sep 10 '14 at 12:43
Btw, `$cordovaGeolocation.getCurrentPosition()` seems to already return a promise. Your code currently is the [deferred antipattern](http://stackoverflow.com/q/23803743/1048572) — Bergi, Sep 10 '14 at 13:01
You can't make an asynchronous operation synchronous. Promises don't do that. They just change the syntax but you still need to pass a callback. Only instead of passing the callback to the asynchronous function the traditional way you pass it to the promise's then function. — slebetman, Sep 10 '14 at 13:05

score 0 · Accepted Answer · answered Sep 10 '14 at 12:43

Since a promise is asynchronous, you can't get its value directly (synchronous) after calling the promise returning function. You could do this

$rootScope.updateDistance = function(lon1, lat1) {
    $cordovaGeolocation.getCurrentPosition()
        .then(function (position) {
            $rootScope.distance = position;
        });
}

Returning the output of a promise

1 Answers1