// The client event 'ValueChanging' takes two parameters sender and e
// sender is the object which is raising the event
// e is the DropDownEditEventArgs
function WebDropDown_ValueChanging(sender, e) {
//Gets the new value in the value display
var newValue = e.getNewValue();
//Gets the old value in the value display
var oldValue = e.getOldValue();
if (!confirm("Are you sure you want to change the curent value from '"+ oldValue+"' to"+newValue+"?"))
//Cancels the ValueChanging client event
e.set_cancel(true);
}