Ajax calls are just like any other HTTP request that might be used to build a web page. However, due to their dynamic nature people often overlook the benefit of caching them.
Rule 14 of High Performance Web Sites states:
Make Ajax Cacheable
Make sure your Ajax requests follow the performance guidelines, especially having a far future [...]
An often overlooked aspect of web performance tuning is the effect of using the HTTPS protocol to create a secure web site. As applications move from the desktop onto the web, the need for security and privacy means that HTTPS is now heavily used by web sites that need to be responsive enough for every [...]
When you setup a web server there are generally two types of caching that you need to configure:
HTML resources are expired immediately so that any changes made to a site are quickly picked up by existing users.
You set everything else (e.g. images, CSS, Javascript) to expire at some distance time in the future.
This caching scheme is covered [...]