In this second instalment I'll explore how and why JavaScript can presents problems for your site's search visibility.

As we have seen, AJAX is reliant on client-side JavaScript, and there needs to be quite a lot of scripting present to enable AJAX.

A common notion regarding JavaScript and search engine optimisation is that it should be avoided, or at least curtail its use to small functions within a site- definitely don't use it for navigation. Why? As with CSS, search engines have difficulty understanding it well enough to use it for rummaging around your site to find pages and keywords. Spiders look for content directly in HTML, not the dynamic content loaded by AJAX.

So, AJAX interferes with the indexing of your site. As AJAX provides data without refreshing or reloading a page it presents non-unique URLs to a search engine. If a page doesn't have a unique URL (i.e. no other page within the site has the same URL) the options to manipulate headers and title tags are diminished. The result? A reduction in visitors - and there is the crux of the AJAX SEO problem.

To work around these issues there are some ideas doing the rounds. I can't comment on their effectiveness, or how they could/should be implemented. What I can say is that people are finding more and better ways to work with AJAX, and as such they should be applauded. Google in particular are exemplary in their use of AJAX.

Here are some AJAX SEO tips:
Avoid DHTML layering and cloaking techniques. DHTML usually relies on JavaScript, and adding more won't help. Cloaking may get you blacklisted from Google- having one site view for visitors and one (plain/html) for spiders is considered spamming- naughty, naughty.

Sadly there doesn't appear to be much in the way of non-technical advice for optimising for AJAX, but if you're brave enough and really, really want to get to grips with AJAX search engine compatibility take a look at using the Hijax development framework.

Also, have a look at how to use the <noscript> tag.

When considering AJAX the first, and most important, question you should ask is "what would AJAX do to benefit my visitors?" If it makes your site more whizzy that's Great, but if it means that your products and services become harder to find then AJAX may not be technology for you.