A lot has been written about caching issues with XMLHttpRequest based apps. There is certainly some amount of frustration and confusion about this topic. I had the same kind of experience when I updated my blog recently to show a paginated blog entry list via an XMLHttpRequest. I noticed that mainstream browsers behave inconsistently when it comes to caching.

In my previous post on HTTP Caching, I left out two topics. The first is caching dynamically generated files (e.g. pdf). The second is choosing headers like Expires, Last-Modified etc.

Over the weekend I was searching a well-known electronics manufacturer's site for an LCD monitor. After finding the product page I was looking for, I bookmarked the page, and then went on to surf something else. After a few minutes, I came back and reloaded the bookmarked page. I expected my browser to load the page immediately from its cache, but it did not. I was curious to find out why. It turned out that the server did not send any cache related HTTP headers, forcing my browser to request for the page again. What a waste of bandwidth and CPU cycles!