difference between setTimeout in javascript and $timeout service in angularjs

Question

Iam new to angular framework.Here is my scenario where, I want to change my $scope.variable after a period of time so i used javascript setTimeout method.

$scope.variable = 'Previous';

setTimeout(function(){
  $scope.variable='NEXT';
},3000);

This code doesn't work for me. I used $apply() to make this code work.

Later I came to know that angular itself has a $timeout service which does the same work.

$scope.variable = 'Previous';

$timeout(function () {
  $scope.variable = 'NEXT';
}, 2000);

How can i compare performance of $timeout service with javascript setTimeout??

Why we should use $timeout instead of setTimeout??

Please give me some examples and reasons to use it, which shows the performance.

Thanks :)

Answer 1

There are some cases where one needs to perform some sort of timeout operation and we frequently achieve this using JavaScript's setTimeout() function.

However, if we use setTimeout() in an AngularJS application we also need to use $scope.$apply() to ensure that any changes to the scope will be reflected elsewhere (i.e. data-bound in a view).

AngularJS provides a handy wrapper for this: $timeout() - it does the $apply() for which we don't have to $apply the changes.

Regarding the performance.

If you're using $timeout to create what is essentially an interval, then don't use it. If your application is large then $apply will also trigger a $digest cycle which you may not really want it to happen, it will surely decrease the performance.

Answer 2

Any AngularJS scope variable when handled from outside (including ajax) needs a $apply().

$timeout() takes care of the current scope and runs in the same digest cycle after all the change detection is done.

One beauty of $timeout() that I recently discovered is, if you do not pass the time parameter, it will wait for the DOM completion.

So,

$timeout(function(){
  console.log("show after directive partial loaded")
}); //note, no time parameter

Run this code in a directive and the timeout callback function will be fired once the partial has been loaded by the directive

Hope this helps.