title: Adding / removing class with slideToggle
body: <p>When clicking on a heading a menu (ul/li) is slided down / up with slideToggle. As background of the heading I have an arrow pointing down if menu isn't visible, up otherwise (I have two classes, 'arrow-up' and 'arrow-down' for the background).</p>
  
  <p>Below is what I've tried but it doesn't work. What would be a good solution?</p>
  
  <pre><code>$j('h3.sub-menu-dropdown-btn').click(function(){
  
      if ($j('ul').is(":visible")) {
          $j(this).removeClass('arrow-up');
          $j(this).addClass('arrow-down');
      } else {
          $j(this).removeClass('arrow-down');
          $j(this).addClass('arrow-up');
      }
  
      $j('.sub-menu-dropdown').slideToggle('fast');
  
  });
  </code></pre>