title: e.dataTransfer is undefined
body: <p>I have a problem with my drag and drop item, when i drag got an error:
  "e.dataTransfer is undefined"</p>
  
  <p>drag function</p>
  
  <pre><code>dragstart: function(e) {
      e.dataTransfer.effectAllowed = 'move';
      e.dataTransfer.dropEffect = 'move';
      e.dataTransfer.setData('application/json', index);
      element.addClass('dragging');
  }
  </code></pre>
  
  <p>Someone know where is the problem?</p>