touch事件如何獲取滑動距離長度

function wetherScroll(){
 var startX = startY = endX =endY =0;
 var body=document.getElementsByTagName("body");
 body.bind('touchstart',function(event){
 var touch = event.targetTouches[0];
 //滑動起點的坐標
 startX = touch.pageX;
 startY = touch.pageY;
 // console.log("startX:"+startX+","+"startY:"+startY);
 });
 body.bind("touchmove",function(event){
 var touch = event.targetTouches[0];
 //手勢滑動時，手勢坐標不斷變化，取最后一點的坐標為最終的終點坐標
 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);
 //移動端設備的屏幕寬度
 var clientHeight; =document.documentElement.clientHeight;
 // console.log(clientHeight;*0.2);
 //判斷是否滑動了，而不是屏幕上單擊了
 if(startY!=Math.abs(distanceY)){
 //在滑動的距離超過屏幕高度的20%時，做某種操作
 if(Math.abs(distanceY)>clientHeight*0.2){
 //向下滑實行函數someAction1，向上滑實行函數someAction2
 distanceY <0 ? someAction1():someAction2();
 }
 }
 startX = startY = endX =endY =0;
 })
}