javascript直接写document，for-in用来枚举，如下图：
<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <script language="Javascript" type="text/javascript" > for (var propName in window) { document.write(propName); document.write("<br/>"); } </script> </head> <body> </body> </html>