<style>
*{padding: 0; margin: 0;}
#div1{ width: 100px; height: 150px; background: red; position: absolute; right: 0;
}
</style>

````
<script>
    window.onscroll=function(){
        var oDiv=document.getElementById("div1");
        var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;
        //oDiv.style.top=(document.documentElement.clientHeight-oDiv.offsetHeight)/2+scrollTop+"px";
        startMove((document.documentElement.clientHeight-oDiv.offsetHeight)/2+scrollTop);
    }
    var timer=null;
    function startMove(iTarget){
        var oDiv=document.getElementById("div1");
        clearInterval(timer);
        timer=setInterval(function(){
            var speed= (iTarget-oDiv.offsetTop)/4;
            speed=speed>0?Math.ceil(speed) : Math.floor(speed);
            if(oDiv.offsetTop==iTarget){
                clearInterval(timer);
            }else{
                document.title=iTarget;
                document.getElementById("txt").value=oDiv.offsetTop;
                oDiv.style.top=oDiv.offsetTop+speed+"px";
            }
        },30);
    }
</script>
````

````