为什么我的无法关闭新窗口
<!DOCTYPE HTML> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>close()</title> <script type="text/javascript"> var mywin; function openUrl() { var mywin=window.open("http://www.imooc.com"); } function closeUrl() { mywin.close(); } </script> </head> <body> <input name="Obutton" type="button" onClick="openUrl()" value="open" /> <br> </br> <input name="Cbutton" type="button" onClick="closeUrl()" value="close" /> </body> </html>