One of the three major pillars of Search Engine Optimization is a website’s content, and onsite content optimization. All of the major search engine ranking algorithms have components that relate to the content that is contained on the website. Typically these components relate to Keyword Densities, number of words, content location, and sometimes age of content. In regards to the code that the content is contained in that falls under the topic of structure and not content, and will not be discussed in this article.
When a search engine sends out a robot / spider to visit your website with the goal of indexing your content it is only looking at what is being presented in the Markup Language. Generally a search engine does not behave like a user when indexing your website, it doesn’t click buttons or links it simply makes note of URLs associated with each page then individually then visits these pages to index them. This largely goes against the goal of AJAX which is to have as few pages as possible by interacting with the web server in a smarter method as the users interact with the website.
Now you may think that I’m anti AJAX from everything that I’ve said, but there are times and places for AJAX, provided it doesn’t affect how the search engines see your beautiful relevant content your trying to rank. AJAX is great to use for Member sections of your website, interactive forms, slideshows, and a lot more it just needs to be leveraged correctly to avoid missing out on search engine visitors. The final thing to keep in mind is that most search engines like to see more than a single page website which many AJAX website appear to be, always strive for at least 5 or more indexable pages as internal links and anchor text can have a lot of value.