angularjs - Angular $scope.$digest vs $scope.$apply

Question

I just want to know how to use $digest. Inside a controller the following code works fine and it updates the DOM after 3 seconds:

setTimeout(function(){
    $scope.$apply(function(){
        $scope.name = 'Alice';
    });
}, 3000);

However by using

setTimeout(function(){
        $scope.$digest(function(){
        $scope.name = 'Alice';
        });
    }, 3000);

nothing happens...

I thought that they do the same thing. Am I wrong?

Answer 1

$apply() and $digest() have some similarities and differences. They are similar in that they both check what's changed and update the UI and fire any watchers.

One difference between the two is how they are called. $digest() gets called without any arguments. $apply() takes a function that it will execute before doing any updates.

The other difference is what they affect. $digest() will update the current scope and any child scopes. $apply() will update every scope. So most of the time $digest() will be what you want and more efficient.

The final difference which explains why $apply() takes a function is how they handle exceptions in watchers. $apply() will pass the exceptions to $exceptionHandler (uses try-catch block internally), while $digest() will require you handle the exceptions yourself.