Как прикрепить div при прокрутке? [без JQuery]

<script>
var t;
function _w_up() { 

  var top = Math.max(document.body.scrollTop,document.documentElement.scrollTop);
  if(top > 0) { 
    window.scrollBy(0,-50);
    t = setTimeout('_w_up()',2);
  } else clearTimeout(t);
  return false;
}
</script>

<style type="text/css">
.btnUp {
    position: fixed;
    right: 40;
    bottom: 0;
    padding: 10px;
    background: 1 solid #000;
    background-color: #eeeeee;
    color: #000;
    min-width: 20px;
}
</style>
<style>
#__goUp {
	background-image: url(/scrollUp/action/png/goUp);
	background-color:transparent;
	width:50px;
	height:12px;
	
}

</style>
<a  onclick="_w_up();"><div id="__goUp" class="btnUp"  style="visibility:hidden">@@UP@@</div></a> 
<script>
  window.onscroll = function(){ 
  	
            document.getElementById('__goUp').style.visibility = (window.pageYOffset >  0 ? '' : 'hidden');
  }
</script>