I need someone's help on this Javascript

Javascript has full access to document cookies. Here's an articles about cookies and Javascript:

http://www.elated.com/articles/javascript-and-cookies/

You can set the cookie in your script, and do a conditional too see if the browser has a valid, unexpired cookie before evaluating the rest of the code.

You have to be careful though because cookies aren't that reliable; for instance if the user uses a different browser the code will run.