title: Backbone custom event callback arguments
body: <p>I'm attempting to pass an argument called newIndex in a custom event from one view to another using the <code>trigger()</code> function.  Here's an excerpt from the first view:</p>
  
  <pre><code>var ProductListView = Backbone.View.extend({
  
      el: '#products',
  
      events:{
              sortupdate: function(event, ui){
                      ui.item.trigger('moved', ui.item.index());
              }
      }
  });
  </code></pre>
  
  <p>The element on which the 'moved' event is being triggered is another view.  Here's an excerpt from that view:</p>
  
  <pre><code>var ProductItemView = Backbone.View.extend({
  
      events: {
              moved: 'viewMoved'
      },
  
      initialize: function(){
              _.bindAll(this, 'render', 'viewMoved');
      },
  
      viewMoved: function(newIndex){
              anotherFunc(this.model, newIndex);
      },
  
  });
  </code></pre>
  
  <p>The issue I'm having is that in the <code>anotherFunc()</code> call, the newIndex argument appears to be the event itself rather than the value that I passed in when I triggered the event.  If I adjust the <code>viewMoved</code> callback to the following, it works correctly:</p>
  
  <pre><code>viewMoved: function(event, newIndex){
      anotherFunc(this.model, newIndex);
  },
  </code></pre>
  
  <p>Is this intended functionality?  Is the event itself always the first argument passed to a custom event's callback, or is something else going on here?  If it's intended is this documented somewhere?  I was unable to find any reference to this in the Backbone documentation.</p>