jquery返回顶部

<a href="javascript：void(0);" id="gotop" class="to_img gotop">顶部</a>

<script type="text/javascript">

//返回顶部

backTop=function (btnId){

var btn=document.getElementById(btnId);

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

window.onscroll=set;

btn.onclick=function (){

btn.style.opacity="0.5";

window.onscroll=null;

this.timer=setInterval(function(){

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

scrollTop-=Math.ceil(scrollTop*0.1);

if(scrollTop==0) clearInterval(btn.timer,window.onscroll=set);

if (document.documentElement.scrollTop > 0) document.documentElement.scrollTop=scrollTop;

if (document.body.scrollTop > 0) document.body.scrollTop=scrollTop;

},10);

};

function set(){

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

btn.style.opacity=scrollTop?'1':"0.5";

}

};

backTop('gotop');

</script>

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