How to close a window with Logoff facility

[szms]

Hi I am trying to close my existing window and before closing it will will show a new mini window where It will be written, press ok if you want to log off. else cancel. And I want to make sure that it really logged of from the server no matter how many other same window is open. By the way I am using unix login system in my web page.

Could you please help me to get this interface. Thank you.