$apply vs $digest in directive testing

Question

If I have a directive that responds to the status of a particular attribute on the scope, and I want to change that attribute in my test and verify that it responds correctly, which is the best way of doing that change?

I've seen both these patterns:

scope.$apply(function() {     scope.myAttribute = true; }); 

and

scope.myAttribute = true; scope.$digest(); 

What is the difference between them, and which is better and why?

Answer 1

scope.$digest() will fire watchers on the current scope, and on all of its children, too. scope.$apply will evaluate passed function and run $rootScope.$digest().

The first one is faster, as it needs to evaluate watchers for current scope and its children. The second one is slower, as it needs to evaluate watchers for$rootScope and all it's child scopes.

When an error occurs in one of the watchers and you use scope.$digest, it's not handled via $exceptionHandler service, so you need to handle exception yourself. scope.$apply uses a try-catch block internally and passes all exceptions to $exceptionHandler.