start(aEvent) {
      aEvent.preventDefault();
      tracking = true;
      orgX = aEvent.changedTouches[0].pageX;
    }

    function move(aEvent) {
      if (!tracking) return;
      newX = aEvent.changedTouches[0].pageX;
      if (orgX - newX > 100) {
        tracking = false;
        this.forward();
      } else {
        if (orgX - newX < -100) {
          tracking = false;
          this.back();
        }
      }
    }
  }

  Dz.setupView = function() {
    document.body.addEventListener("click", func