Which browsers have problems caching XMLHTTPRequest responses?

Question

Do any of the currently popular browsers have particular problems caching* XMLHttpRequest responses that I need to be aware of?

I'd like to be able to include XMLHttpRequest queries on every page as a method of dynamically loading content (ie JSON) or behaviour (like eval()ed Javascript) relevant to the type of page, but wanted to make sure that the resources it receives from the server could be cached, if the server sent the right headers.

I was concerned to read this article which mentions that browsers such as Firefox 1.1 do not cache any content obtained via XMLHTTPRequest, and that it always requests new data is sent completely (with Cache-Control and no If-Modified-Since) regardless of headers sent by the server.

Obviously that article is very old - I don't even remember a Firefox 1.1; so what are the considerations I need to make for current popular browsers and is there any trick for when I specifically want responses to be cached?

*To clarify my question, by caching, I mean client-side caching, where the server issues freshness information (in the form of a Cache-Control: max-age directive or an Expires: header) and the browser stores a copy of the response in its cache along with an expiry date, so that future requests for the same resource issued from subsequent pages can be satisfied from the browser cache without the need for any contact with the server at all. All major browsers do this correctly for most content, but I've heard that Firefox cannot do this for XMLHttpRequest content. What I'm asking is if anyone knows of cases where any of the modern browsers do not cache responses according to the spec when using XMLHttpRequest.

Answer 1

Although some browsers have different defaults (by default, IE will cache results from AJAX requests, but Firefox, by default, will not), all browsers that I'm aware of will obey the http headers, such as Cache-Control. So just set the caching headers correctly for your application.

Here is an example:

    public ActionResult SomeAction()
    {
        var model = [...];
        Response.AddHeader("Cache-Control", "no-cache");
        return Json(model);
    }

Now IE and Firefox will both behave the same; they will never cache the results of the action.

Answer 2

I have had a few experiences with earlier verions of IE (5.5 - 6) caching ajax GETs (I was using Prototype JS Ajax.Request) and found that changing the request type to POST solved the problem.

I have also read in several places that to be on the safe side, or if there is any uncertainty, to use POST instead.

You can use Firebug to determine if the content is being reloaded or not.

Answer 3

Mark Nottingham has an excellent set of functional tests that demonstrate browser XMLHttpRequest caching behaviour. Load up the page in the browsers you want to support and work out what techniques you can and cannot rely on to have your response cached.