AngularJS Web Application Development Cookbook

Creating promise wrappers with $q.when()

AngularJS includes the $q.when() method that allows you to normalize JavaScript objects into promise objects.

How to do it…

The $q.when() method accepts promise and non-promise objects, as follows:

var deferred = $q.defer()
  , promise = deferred.promise;

$q.when(123);
$q.when(promise);
// both create new promise objects

If $q.when() is passed a non-promise object, it is effectively the same as creating an immediately resolved promise object, as shown here:

var newPromise = $q.when(123); // promise will wait for a $digest cycle to update $$state.status, // this forces it to update for inspection $scope.$apply(); // inspecting the status reveals it has already resolved $log.log(newPromise.$$state.status); // 1 ...