AngularJS - Callback after ng-repeat update - angularjs

Question

I got some trouble understanding how I make a callback after I've updated an ng-repeat. I basically want to be able to make a callback function after my updates to my ng-repeat has been finished. Currently have this:
var app = angular.module('myApp', []);
app.directive('onLastRepeat', function() {
return function(scope, element, attrs) {
if (scope.$first)
console.log("ng-repeat starting - Index: " + scope.$index)
if (scope.$last) setTimeout(function(){
console.log("ng-rpeat finished - Index: " + scope.$index);
}, 1);
};
});
app.controller('MyController', function($scope) {
$scope.data = [1,2,3,4,5,6,7,8,9,10,12,12,13,14,15,16,17,18,19,20];
$scope.buttonClicked = function() {
console.log('Btn clicked');
$scope.randomItems = getRandomItems(this.data.length);
};
});
HTML
<div ng-app="myApp">
<div ng-controller="MyController">
<button ng-click="buttonClicked()">Highlight random</button>
<ul class="item" >
<li ng-repeat="item in data" ng-class="{highlight: randomItems.indexOf($index) > -1}" on-last-repeat>{{ item }} </li>
</ul>
</div>
</div>
Link to fiddle: https://jsfiddle.net/hbhodgm3/
So how the "app" works is that it lists the content of the data-array then when you click the "highlight"-button it randomly highlights 2 in the list. So my problem is that I want to have a callback function for when the highlighting/DOM-render is done. I found a way to do this for the initial ng-repeat with $scope.first and $scope.last to check when ng-repeat is done, but doesn't seem to work with the highlighting.
Hope I managed to explain the problem,
Thanks in advance.

Answer 1

See $q and Promises for a better understanding of how to work with the asynchronous nature of angular.
Presuming getRandomItems(this.data.length); is an API call that could take seconds to perform:
asyncItems(this.data.length).then(function(randoms){
$scope.randomItems = randoms;
//handle post rendering callback
});
function asyncItems(length) {
var deferred = $q.defer();
var items = getRandomItems(length);
if (items){
deferred.resolve(items);
}
else {
//no items :(
deferred.reject([]);
}
return deferred.promise;
}