title: AngularJS $watch variable and reevaluate ng-class expression
body: <p>I'm trying to implement a bookmark-like function into my app and have to watch a variable, which stores all the bookmarked ID's. Based on that variable I have to tell <code>ng-class</code> to reevaluate it's function expression so the class <code>bookmarked</code> get's added or not.</p>
  
  <p>How do I tell <code>ng-class</code> to run again when the variable <code>$scope.Bookmarks</code> changes?</p>
  
  <pre><code>&lt;a ng-repeat="event in events"
     ng-class="isBookmarked(event.id)"
     class="icon__bookmark"&gt;&lt;/a&gt;
  </code></pre>