Javascript -- 彈出層跟隨滾動條滾動

window.setInterval(function moveWithScroll() {

       var scrollDiv = document.getElementById('div_Atheletebox');

       if (scrollDiv.style.display == "block") {

var w = document.documentElement.clientWidth;
var h = document.documentElement.clientHeight;
var ow = scrollDiv.style.width;
var oh = scrollDiv.style.height;
var scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop || 0;
var nowW = (w - parseInt(ow)) / 2;
//var nowH = (scrollTop + h - parseInt(oh)) / 2;
var nowH = (h - parseInt(oh)) / 2 + scrollTop;
scrollDiv.style.left = nowW + "px";
scrollDiv.style.top = nowH + "px";
}

}, 50);