mywin 变量是干嘛的？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>close()</title>
<script type="text/javascript">
var mywin=window.open("http://www.imooc.com");
mywin.close()
</script>
</head>
<body>
</body>
</html>
