javascript01-div居中的兼容有关问题，发一个奇怪的代码，可能是小弟我没有理解精髓吧 _JavaScript

javascript01-div居中的兼容问题，发一个奇怪的代码，可能是我没有理解精髓吧。

天做项目需要用的一个div居中，下面一个模态层的问题，我写了个代码，大概分离出来如下。

view sourceprint?

<html xmlns="http://www.w3.org/1999/xhtml"> 

<head runat="server"> 

????<title></title> 

????<style type="text/css"> 

????????div 

????????{ 

????????????width: 200px; 

????????????height: 300px; 

????????????background: red; 

????????????border: 1px solid black; 

????????} 

????</style> 

</head> 

<body> 

????<div> 

????</div> 

????<div> 

????</div> 

????<div id="d" style="position: absolute; width: 200px; height: 300px;"> 

????</div> 

????<script type="text/javascript"> 

????????var pageWidth = 0; 

????????var pageHeight = 0; 

????????var left = "0px"; 

????????var top = "0px"; 

????????var divWidth = 0; 

????????var divHeight = 0; 

????????var d = document.getElementById("d"); 

????????if (d) { 

????????????//??????? divWidth = (d.style.width.toString()).replace("px", ""); 

????????????//??????? divHeight = (d.style.height.toString()).replace("px", ""); 

????????????divWidth = parseInt(d.style.width.toString()); 

????????????divHeight = parseInt(d.style.height.toString()); 

????????} 

????????if (document.compatMode == "CSS1Compat") { 

????????????pageWidth = parseInt(document.documentElement.clientWidth); 

????????????pageHeight = parseInt(document.documentElement.clientHeight); 

????????} else { 

????????????pageWidth = parseInt(document.body.clientWidth); 

????????????pageHeight = parseInt(document.body.clientHeight); 

????????} 

????????left = ((pageWidth - divWidth) / 2).toString() + "px"; 

????????top = ((pageHeight - divHeight) / 2).toString()+"px"; 

????????d.style.left = left 

????????d.style.top = ((pageHeight - divHeight) / 2).toString() + "px";//goog浏览器不得行???? 

????????d.innerHTML = "pageWidth:" + pageWidth + "<br/> pageHeight:" + pageHeight + "<br/> divWidth:" + divWidth 

?????+ " <br/>divHeight:" + divHeight + " <br/>left:" + left + " <br/>top:" + top; 

????</script> 

</body> 

</html>

　　?d.style.top = ((pageHeight - divHeight) / 2).toString() + "px";//goog浏览器不得行????

请注意这段代码，这个代码在IE，火狐，google浏览器下都没有问题，但是将这句改成

　 d.style.top = top；

google就错了。不知道什么原因？求解答。