返回顶部注意事项

<script>
// 返回顶部注意事项

var oDiv = document.getElementById('box');
var iTimer = null;
var flag = 0;
setTop();

//滚动条事件</span>
window.onscroll = function(){
//不是定时器触发，清除定时器
if(flag !=1){
clearInterval(iTimer);
}
flag = 2;
setTop();
}

oDiv.onclick = function(){
clearInterval(iTimer);
var iCur = iSpeed = 0;
iTimer = setInterval(function(){
iCur = document.documentElement.scrollTop || document.body.scrollTop;
iSpeed = Math.floor((0 - iCur )/8;
if(iCur == 0){
clearInterval(iTimer);
}else{
document.documentElement.scrollTop = document.body.scrollTop = iCur + iSpeed;
//定时器操作标识
flag = 1;
},30);
}

// 算法 = 滚动条高度 + 可视区高度 - 当前对象的高度
function setTop(){
var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
oDiv.style.top = scrollTop + document.documentElement.clientHeight - oDiv.offsetHeight + 'px';
}
</script>