<!DOCTYPE html>
<html>
<head>
<title> new document </title>
<meta http-equiv="Content-Type" content="text/html; charset=gbk"/>
<script type="text/javascript">
function openWindon(){
var oopp=prompt("打开：","");
if(oopp=null)
{alert("nihao");}
else
{alert("buhao");}}
</script>
</head>
<body>
<form>
<input type="button" value="新窗口打开网站" onclick="openWindon()" />
</form>
</body>
</html>
无论点击确定还是取消都是弹出“不好”，怎么回事？
