title: How to set ngClass based on Bootstrap's collapse?
body: <p>I use <a href="http://getbootstrap.com/javascript/#collapse" rel="nofollow">collapse plugin</a> from Bootstrap, and i also want to change class for another element accordingly (change class of fa-icon). 
  I also use AngularJS and i liked the idea of using condition in ngClass like this:</p>
  
  <pre><code>&lt;i ng-class="collapsableItemId.hasClass('in') ? 'fa-chevron-up' : 'fa-chevron-down'"&gt;
  </code></pre>
  
  <p>When item is not collapsed bootstrap adds <code>in</code> class to it. I want to try to change icon based on class presence in collapsable item, but did not succeed in it. In bootstrap manual there is also mentioned that collapse generates <a href="http://getbootstrap.com/javascript/#collapse-events" rel="nofollow">events</a> which i could probably use, but i also do not know how.</p>