code: function addListener(element, listener) {
          var id = idHandler.get(element);
  
          if(!eventListeners[id]) {
              eventListeners[id] = [];
          }
  
          eventListeners[id].push(listener);
      }
docs: Stores the given listener for the given element. Will not actually add the listener to the element.
  @public
  @param {element} element The element that should have the listener added.
  @param {function} listener The callback that the element has added.