用javascript来检测你在页面上的发呆时间(jquery插件)
There are a few cases where you want to know if the user is idle. Namely:

• You want to preload more assets[*]
• You want to grab their attention to pull them back[*]
• You want close their banking session after 5 minutes of inactivity. (Jerk!)[*]
• You want the site to sneak off the screen and see if they notice ;-)[*]

http://paulirish.com/2009/jquery-idletimer-plugin/

Nick Zakas wrote a script for YUI3