Now How to Make AJAX Cacheable:
The browser will cache AJAX queries just as it would regular HTTP queries on the client side. To enable this behavior, your application must make use of the “cache control” headers, and the “expires” header when serving the AJAX response. You can also use the last fetch time that’s sent as a request header to determine if you can respond with a 304 response. If you’re mostly concerned with the database fetch time, you can use a query caching system like memcached to speed up responses, or even cache results so that you can quickly send the same body back on the same request set.
It turns out that these techniques are exactly the same as standard HTTP, because AJAX is nothing more than regular old HTTP calls that return (typically) JSON, XML or partial HTML content instead of full HTML pages.