//The client side event Collapsing takes two parameters, sender and e.
//Sender is the object which is raising the event
//e is the SplitterCollapsedStateEventArgs
function WebSplitter1_Collapsing(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 collapse the pane
if(!confirm("Do you want to continue collapsing the pane?"))
e.set_cancel(true);
// Gets the collapsed state of the pane
// Boolean value, true is collapsed, false is not collapsed
var collapsed = websplitterPane.get_collapsed();
// Gets the collapsed direction of the pane
// 1 is nextPane, 2 is previousPane
var collapsedDirection = websplitterPane.get_collapsedDirection();
}