这是一个打开和关闭新窗口的例子，里面我有疑惑，请求助。

<head>
<script type="text/javascript">
function dk(){
var myWeb=window.open("","","width=500,height=500");
myWeb.document.write("This is 'poem'");
myWeb.document.write("<img src=\"images/Koala.jpg\"/>");
return myWeb;
}

function closeWin()
{
myWeb.close(); //怎么改才对？
}
</script>
</head>
<body>
<a href="#" onclick="dk()">openweb</a>
<a href="#" onclick="closeWin()">closeweb</a>

</body>