anybody know how to add a cancel button on a suitelet using 2.0. This code does not work:

var cancel_url = url.resolveTaskLink({
                    id: 'CARD_-29'
               });
               var cancel_function = "window.open('" + cancel_url + "')";

               form.addButton({
                    id: 'custpage_cancel',
                    label: 'Cancel',
                    script: cancel_function
               });