title: Do superfluous calls to addEventListener("event", thisSpecificFunction) waste resources?
body: <p>I have ItemRenderers that need to listen for events. When they hear an event (and when data changes), they dispatch an event with their current data value.</p>
  
  <p>As item renderers are reused, each of them is going to add its callback in <code>set data(value...)</code>and pass the callback function in the event as well as the current data value.</p>
  
  <p>So, the listener of the item renderer's bubbling event will set someEventDispatcher.addEventListener("someEvent", itemRendererEvent.callbackListener). This will happen more than once.</p>
  
  <p>Does setting the same event listener on the same event for the same dispatcher waste resources? Does the displatcher see that it already has the listener?</p>