// The client side event SplitterBarMouseDown takes two parameters, sender and e.
// Sender is the object which is raising the event
// e is the EventArgs
function WebSplitter1_SplitterBarMouseDown(sender, e) {
var websplitter = $find("WebSplitter1");
// Get the orientation of the websplitter, 0 is horizontal, 1 is vertical
var orientation = websplitter.get_orientation();
// Get reference to pane located at index 0
var websplitterPane = websplitter.getPaneAt(0);
// If orientation is horizontal, lock the pane from moving
if (orientation == "0")
websplitterPane.set_locked(true);
}