Javascript is a scripting language used mainly to add extra ( cool ) features to web applications, I deliberately said applications as I do not consider web pages loaded with javascript mere documents. These javascript filled web pages are actually like I said little applications used on the web. I could go on and on about how javascript can improve the website for the users and it does help. The problem however is that well written javascript applications are time consuming to develop and totally useless for us seo web developers. The main search engines do not read nor execute javascript code, with the exception of some small fragments. My advice is keep your javascript to a minimum and develop and test your site with javascript turned of, you can do this very easily with the firefox web browser from mozilla. If your site and more importantly your navigation works properly with no javascript the search engine spiders will spider your site as easily as if they were taking candy from a baby. Good luck and happy seo ing.