// Menu select
function YourFunction(sender, eventArgs)
{
    // Get all menu items
    var rootItems = PageMenu.get_items();

    // Reset lookid's
    for (var i = 0; i < rootItems.get_length(); i++)
    {
        rootItems.getItem(i).setProperty("LookId","TopItemLook");
    }

    // Select current
    eventArgs.get_item().setProperty("LookId","SelectedItemLook");
}