我想在页面加载的时候设置frame的src怎么没效果

<%@ page contentType="text/html; charset=gb2312"%>
<script type="text/javascript" src="../../resource/js/Common.js"></script>
<script>
    window.resizeTo(screen.availWidth,screen.availHeight);

document.attachEvent("onreadystatechange",  function(event){
    if (document.readyState == "interactive" || document.readyState == "complete"){
document.detachEvent("readystatechange", arguments.callee);

window.mainFrame.src = "../../privilege_func_desc.html?privilege_id=100";
    }
});
</script>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>知识库管理</title>
</head>
<frameset cols="220,*" frameborder="0" framespacing="1">
  <frame src="knowledgeCatalogTree.html" name="leftFrame" scrolling="auto" style="border-right:1px solid #C4C4C4">
  <frame src="about:blank" name="mainFrame" id="mainFrame" FRAMEBORDER="0" style="border-left:1px solid #C4C4C4">
</frameset>
<noframes><body>
</body></noframes>
</html>
我想在页面加载的时候设置frame的src怎么没效果，见红色部分