wordpress返回顶部的功能

#gotop{
    width:38px;
    height:36px;
    position:fixed;
    bottom:25px;
    right:10px;
    top:auto;
    display:block;
    cursor:pointer;
    background: url(images/gotop.gif) no-repeat
}

*html #gotop{
    position:absolute;
    bottom:auto; top:expression(eval(document.documentElement.scrollTop+document.documentElement.clientHeight-this.offsetHeight-(parseInt(this.currentStyle.marginTop,10)||0)-(parseInt(this.currentStyle.marginBottom,10)||0)));
}

<!-- 返回顶部 -->
<div style="display: none;" id="gotop"></div>
<script type=‘text/javascript‘>
    backTop=function (btnId){
        var btn=document.getElementById(btnId);
        var d=document.documentElement;
        var b=document.body;
        window.onscroll=set;
        btn.onclick=function (){
            btn.style.display="none";
            window.onscroll=null;
            this.timer=setInterval(function(){
                d.scrollTop-=Math.ceil((d.scrollTop+b.scrollTop)*0.1);
                b.scrollTop-=Math.ceil((d.scrollTop+b.scrollTop)*0.1);
                if((d.scrollTop+b.scrollTop)==0) clearInterval(btn.timer,window.onscroll=set);
            },10);
        };
        function set(){btn.style.display=(d.scrollTop+b.scrollTop>100)?‘block‘:"none"}
    };
    backTop(‘gotop‘);
</script>
<!-- 返回顶部END -->