//The client side event Expanding takes two parameters, sender and e.
//Sender is the object which is raising the event
//e is the SplitterPaneExpandedEventArgs
function WebSplitter1_Expanding(sender, e) {
var websplitter = $find("WebSplitter1);
// Gets a reference to the pane that is related to the browser event in
// the splitter bar
var websplitterPane = websplitter.getPaneFromEvent(e);
// Confirm if end user wants to expand the pane
if (!confirm("Do you want to continue expanding the pane?"))
e.set_cancel(true);
// Gets the size of the expanded pane
var size = websplitterPane.get_size();
window.status = "Size of expanded pane "+ size;
}