Executing $digest() After the Scheduled Function Call

If the function you schedule for execution makes changes to variables in the $scope object, or make changes to any other variable which your application is watching, your application needs to execute $scope.$digest() after the scheduled function call finishes. Why that is necessary is explained in my tutorial about $watch(), $digest() and $apply().

By default AngularJS already calls $digest() after the scheduled function call finishes, so you don't have to do that explicitly. You can, however, specify if AngularJS should not call $digest() after the scheduled function call. If, for instance, your scheduled function call only updates an animation but does not change any $scope variables, then it is a waste of CPU time to call $digest() after the function finishes.

Both $timeout and $interval have a third, optional parameter which can specify if the $digest() method is to be executed after the scheduled function finishes. Actually, the third parameter specifies if the call to the scheduled function should be done inside an $apply() call. Here is an example of how to use this third parameter:

$interval( function(){ $scope.callAtInterval(); }, 3000, true);

$interval( function(){ $scope.callAtInterval(); }, 3000, false);

These two $interval examples both have a third parameter passed to the $interval service. This parameter can be either true or false. A value of true means that the scheduled function should be called inside an $apply() call. A value of false means that it should not be called inside an $apply() call (meaning $digest() will not get called after the scheduled function finishes).