Angularjs: Performance using ng-class

Question

This is a dummy coding that describes my problem
HTML

<div ng-class="{'test': isAllowed }" id='example1'>Example 1</div>
<div ng-class="{'test': isAllowed }" id='example2'>Example 2</div>

$scope.isAllowed is evaluated completely, and #example1 is affected by the class test, but sometimes it takes time for #example2 to be affected by that class, although both of them share same class. I think the problem is with ng-class.
I can fix my problem using ng-if

<div class="test" ng-if="isAllowed" id='example1'>Example 1</div>
<div ng-if="!isAllowed" id='example1'>Example 1</div>
<div class="test" ng-if="isAllowed" id='example2'>Example 2</div>
<div ng-if="!isAllowed" id='example2'>Example 2</div>

As you can see, It looks redundant, and I don't want to deal with the problem in this way

Answer 1

How is isAllowed being set? If it's being set within a setTimeout, setInterval, or something else that is outside of the angular lifecycle, you may need to include a

scope.$apply()

(if its a directive), or

$scope.$apply()

(if its in a controller) after you have set the isActive.

$scope.isActive = true;
$scope.$apply();

If neither of those two work, or if you get a "already in a digest cycle" error, then wrap with an $evalAsync

$scope.$evalAsync(function(){
    $scope.isActive = true;
});

Check out https://jsfiddle.net/cyx4z03m/1/ You will see that the css is not being updated except once every 3 seconds. Open your DevTools and check out the console log. The value is being toggled, but you dont see the real result until angular knows its ready to update. I'm wondering if your issue is related.