//The client side event Expanded takes two parameters, sender and e.
//Sender is the object which is raising the event
//e is the SplitterPaneExpandedEventArgs
function WebSplitter1_Expanded(sender, e) {
var websplitter = $find("WebSplitter1");
// Gets a reference to the pane whose expanded state was changed
var websplitterPane = e.get_pane();
// Gets the index of the pane whose expanded state was changed
var paneExpandedIndex = websplitterPane.get_index();
window.status = "Pane Expanded Index " + paneExpandedIndex;
// Lock the pane so that it cannot be resized after it is expanded
websplitterPane.set_locked(true);
}