AngularJS promises returning object rather than resolved value

Question

function times() {
  var deferred = $q.defer();

  var data = $http.get('https://bus.data.je/latest');

  data.success(function(_data) {
    deferred.resolve(_data);
  });

  data.error(function(error) {
    deferred.reject(error);
  });

  return {
    all: function() {
      return deferred.promise;
    },

    timetable: function(type) {
      _data = deferred.promise;
      return _data.filter(function (el) {
        el = el[0];
        return el.MonitoredVehicleJourney.DirectionRef == type;
      });
    }
  }
}

When either return functions are queried, it returns an object containing promise functions (finally, catch and then), rather than the resolved value. How do I fix this?

Avoid the Deferred antipattern! Hint: all references to deferred.promise could simply be replaced by data. — Bergi
– Bergi, Commented Sep 27, 2014 at 19:04
You cannot synchronously get the resolution value of a promise back. Promises are still asynchronous, all you can do is to derive another promise from them. — Bergi
– Bergi, Commented Sep 27, 2014 at 19:05

Rytmis · Accepted Answer · 2014-09-27 19:17:55Z

You don't. What you do is expose your own API as promise-based:

function times() {
    var deferred = $q.defer();

    var data = $http.get('https://bus.data.je/latest');

    data.success(function(_data) {
        deferred.resolve(_data);
    });

    data.error(function(error) {
        deferred.reject(error);
    });

    return {
        all: function() {
            return deferred.promise;
        },

        timetable: function(type) {
            return deferred.promise.then(function (data) {
                return data.filter(function (el) {
                    el = el[0];
                    return el.MonitoredVehicleJourney.DirectionRef == type;
                });
            });
        }
    }
}

and then use it like so:

times.timetable().then(function (timetables) { /* work with the timetables here */ });

Because, like the comments pointed out, you can't make promises synchronous after the fact.

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