// The client event 'ActivationChanging' takes two parameters sender and e
// sender is the object which is raising the event
// e is the DataTreeActivationEventArgs
function WebDataTree_ActivationChanging(sender, e) {
//Gets the new active Node object
var newActiveNode = e.getNewActiveNode();
//Gets the text of the new active node
var newNodeText = newActiveNode.get_text();
if (!confirm("Are you sure you want to activate the node'" + newNodeText + "'?"))
//Cancels the ActivationChanging event
e.set_cancel(true);
}