How to calculate sliding distance using touch event on JS mobile phone

function wetherScroll(){
    var startX = startY = endX =endY =0;
    var body=document.getElementsByTagName("body");
    body.bind('touchstart',function(event){
      var touch = event.targetTouches[0];
      //滑动起点的坐标
      startX = touch.pageX;
      startY = touch.pageY;
      // console.log("startX:"+startX+","+"startY:"+startY);
    });
    body.bind("touchmove",function(event){
      var touch = event.targetTouches[0];
      //手势滑动时，手势坐标不断变化，取最后一点的坐标为最终的终点坐标
        endX = touch.pageX;
        endY = touch.pageY;
        // console.log("endX:"+endX+","+"endY:"+endY);
    })
    body.bind("touchend",function(event){
      var distanceX=endX-startX,
        distanceY=endY - startY;
        // console.log("distanceX:"+distanceX+","+"distanceY:"+distanceY);
        //移动端设备的屏幕宽度
        var clientHeight; =document.documentElement.clientHeight;
        // console.log(clientHeight;*0.2);
        //判断是否滑动了，而不是屏幕上单击了
        if(startY!=Math.abs(distanceY)){
 //在滑动的距离超过屏幕高度的20%时，做某种操作
          if(Math.abs(distanceY)>clientHeight*0.2){
 //向下滑实行函数someAction1，向上滑实行函数someAction2
          distanceY <0 ? someAction1():someAction2();
        }
        }
        startX = startY = endX =endY =0;
    })
}