ASP.NET Ajax: close window after Ajax call?

sm.RegisterDataItem(ActionLabel, "action:closewindow")

function PageLoadingHandler(sender, args)
{
    var dataItems = args.get_dataItems();
    if (dataItems['ActionLabel'] == 'action:closewindow') {
        window.close()
    }
}
Sys.WebForms.PageRequestManager.getInstance().add_pageLoading(PageLoadingHandler);