docs: function getDirection(beforeOffset, nowOffset) {
      var direction = 'none';
      var horizental = beforeOffset.left - nowOffset.left;
      var vertical = beforeOffset.top - nowOffset.top;
      if (vertical == 0) {
        if (horizental != 0) {
          direction = horizental > 0 ? 'left' : 'right';
        } else {
          direction = 'none'
        }
      }
      if (horizental == 0) {
        if (vertical != 0) {
          direction = vertical > 0 ? 'up' : 'down';
        } else {
          direction = 'none';
        }
      }
      return direction;
    }