jquery判斷手機端手指上下滑動方向

<script type="text/javascript">
    $(document).ready(function(){

      function GetSlideDirection(startX, startY, endX, endY) {  
      var dy = startY - endY;  
      //var dx = endX - startX;  
      var result = 0; 
      if(dy>0) {//向上滑動
              result=1;
      }else{//向下滑動
              result=2;
      }
      return result;  
  } 

  //滑動處理  
    var startX, startY;  
    document.addEventListener('touchstart',function (ev) {  
        startX = ev.touches[0].pageX;  
        startY = ev.touches[0].pageY;    
    }, false);  

    
    
    document.addEventListener('touchend',function (ev) {  
        var endX, endY;  
        endX = ev.changedTouches[0].pageX;  
        endY = ev.changedTouches[0].pageY;  
        var direction = GetSlideDirection(startX, startY, endX, endY);
        switch(direction) {  
            case 0:  
                break;  
            case 1:  
                // 手指向上滑動
                //alert('上');break;  
            case 2:  
                // 手指向下滑動
                //alert('下');break;  
            default:             
        }  
    }, false); 
      });
</script>