var mywin=window.open('http://www.imooc.com'); 可以打开窗口，mywin没有被赋值？
<script type="text/javascript">var mywin=window.open('http://www.imooc.com'); mywin.close();</script>
网页错误详细信息
用户代理: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.3; .NET4.0C; .NET4.0E)
时间戳: Tue, 2 May 2023 02:54:29 UTC
消息: 'mywin' 为空或不是对象
行: 8
字符: 5
代码: 0
URI: file:///D:/MyWeb/学习JS/2-6.html
