为什么两个else就不能运行呢？每个if语法对应一个else不行吗？
<!DOCTYPE html>
<html>
<head>
<title> new document </title>
<meta http-equiv="Content-Type" content="text/html; charset=gbk"/>
<script type="text/javascript">
function openwindow()
{ var open = confirm("确认打开新窗口");
if(open==true){var url = prompt("打开网址是否正确"，"http//：www.imooc.com")}
if(url!=null){window.open(url,"_blank",'width=400px,height=500px,menubar=no,toolbar=no');}
else{alert("再见");}
else{alert("再见");}
}
</script>
</head>
<body>
<input type="button" value="新窗口打开网站" onclick="openWindow()" />
</body>
</html>
