window.onload=function(){

var bot =document.getElementById("return");

var timer=null;

var isTop=true;

var cheight=document.documentElement.clientHeight||document.body.clientHeight;

//点击事件

bot.onclick=function(){

//鼠标滚动时间

window.onscroll=function(){

var sctop = document.documentElement.scrollTop||document.body.scrollTop;

if(scTop>=cheight){

bot.style.display="block";

}else{

bot.style.display="none";

}

if(!isTop){

clearInterval(timer);

}

isTop=false;

}

//定时器

timer = setInterval(function(){

var sctop = document.documentElement.scrollTop || document.body.scrollTop;

var speed = sctop/6;

document.documentElement.scrollTop=document.body.scrollTop = sctop-speed;

isTop=true;

if (sctop==0)

{

clearInterval(timer);

}

},50);

}

clearInterval(timer);

}

为什么最后的隐藏显示实现不了啊