UrlLoadRequest プロパティ

// The client event UrlLoadRequest takes two parameters sender and e
// sender  is the object which is raising the event
// e is the TabItemEventArgs

function WebTab1_UrlLoadRequest(sender, e) {

               //Gets the index of the tab involved in the event
               var tabIndex = e.get_tabIndex();

               //Assuming you have a label called labelOutput on the form
     var label = $get('labelOutput');

               label.innerHTML =  "Url load request for tab with index '" + tabIndex + "'...";

           }