code: function start(tour) {
              if (!tour) {
                  $q.reject('No Tour Specified!');
              }
              if (!tour.steps.length) {
                  $q.reject('No steps were found in that tour!');
              }
              if (service.current) {
                  return stop()
                      .then(function() {
                          return startTour(tour);
                      });
              } else {
                  return startTour(tour);
              }
          }
docs: API