touch事件计算滑动距离

计算手势在手机屏幕上滑动时，手势滑动的距离，代码如下：

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;        })    }