JavaScript® Bible, Seventh Edition

Chapter 57. Application: Intelligent "Updated" Flags

IN THIS CHAPTER

• Temporary and persistent cookies

• World time calculations

• CGI-like intelligence

It happens to every active web user all the time: You visit a site periodically and never know for sure what material is new since your last visit. Often, web page authors may flag items with "New" or "Updated" iconic images after they update those items themselves. But if you fail to visit the site over a few modification sessions, the only items you find flagged are those that are new as of the most recent update by the page's author. Several new items from a few weeks back may be of vital interest to you, but you won't have the time to look through the whole site in search of material that is more recent than your last visit. Even if the items display their modification dates, do you remember for sure the date and time of your last visit to the page?

As much as we might expect a server-side program and database on a web site to keep track of my last visit, that really is asking a great deal of the web site. Besides, not every web site has the wherewithal to build such a database system—if it can even utilize server applications. Plus, some users won't visit sites if they need to identify themselves or register.

After surveying the way scriptable browsers store cookie information and how time calculations are performed under popular web browsers, I found that a feasible alternative is to build this functionality into HTML documents and let ...