Js 回到顶部的方法

<script type="text/javascript"><!--
var w = 270;
var h = 20;
var str = "";
var obj = document.getElementById("divStayTopLeft");
if (obj)str = obj.innerHTML;
if( typeof document.compatMode != 'undefined' && document.compatMode != 'BackCompat'){
document.writeln('<DIV  style="z-index:9;right:0;bottom:0;height:'+h+'px;width:'+w+'px;overflow:hidden;POSITION:fixed;_position:absolute; _margin-top:expression(document.documentElement.clientHeight-this.style.pixelHeight+document.documentElement.scrollTop);">');
}
else {
document.writeln('<DIV  style="z-index:9;right:0;bottom:0;height:'+h+'px;width:'+w+'px;overflow:hidden;POSITION:fixed;*position:absolute; *top:expression(eval(document.body.scrollTop)+eval(document.body.clientHeight)-this.style.pixelHeight);">');
}
document.writeln('<div style="clear:both;margin:auto;height:30px;font-size:16px;overflow:hidden;font-weight:bold;text-align:left;"><a href="javascript:scroll(0,0)" hidefocus="true"><img src="TOP图片地址" alt="" title="回到顶部" style="border: 0px;" /></a></div> ');
document.write('<div style="clear:both;margin:auto;overflow:hidden;text-align:left;">'+str+'</div>');
document.writeln('</DIV>');
-->
</script>

转自：http://mywillow.cn/code-and-icon-return-to-top/