I had this same question, and found some info in my searches (your question came up as one of the results). Here's what I determined...
There are two sides to the Cache-Control
header. One side is where it can be sent by the web server (aka. "origin server"). The other side is where it can be sent by the browser (aka. "user agent").
When sent by the origin server
I believe max-age=0
simply tells caches (and user agents) the response is stale from the get-go and so they SHOULD revalidate the response (eg. with the If-Not-Modified
header) before using a cached copy, whereas, no-cache
tells them they MUST revalidate before using a cached copy. From 14.9.1 What is Cacheable:
no-cache
...a cache MUST NOT use the response
to satisfy a subsequent request
without successful revalidation with
the origin server. This allows an
origin server to prevent caching even
by caches that have been configured to
return stale responses to client
requests.
In other words, caches may sometimes choose to use a stale response (although I believe they have to then add a Warning
header), but no-cache
says they're not allowed to use a stale response no matter what. Maybe you'd want the SHOULD-revalidate behavior when baseball stats are generated in a page, but you'd want the MUST-revalidate behavior when you've generated the response to an e-commerce purchase.
Although you're correct in your comment when you say no-cache
is not supposed to prevent storage, it might actually be another difference when using no-cache
. I came across a page, Cache Control Directives Demystified, that says (I can't vouch for its correctness):
In practice, IE and Firefox have
started treating the no-cache
directive as if it instructs the
browser not to even cache the page.
We started observing this behavior
about a year ago. We suspect that
this change was prompted by the
widespread (and incorrect) use of this
directive to prevent caching.
...
Notice that of late, "cache-control:
no-cache" has also started behaving
like the "no-store" directive.
As an aside, it appears to me that Cache-Control: max-age=0, must-revalidate
should basically mean the same thing as Cache-Control: no-cache
. So maybe that's a way to get the MUST-revalidate behavior of no-cache
, while avoiding the apparent migration of no-cache
to doing the same thing as no-store
(ie. no caching whatsoever)?
When sent by the user agent
I believe shahkalpesh's answer applies to the user agent side. You can also look at 13.2.6 Disambiguating Multiple Responses.
If a user agent sends a request with Cache-Control: max-age=0
(aka. "end-to-end revalidation"), then each cache along the way will revalidate its cache entry (eg. with the If-Not-Modified
header) all the way to the origin server. If the reply is then 304 (Not Modified), the cached entity can be used.
On the other hand, sending a request with Cache-Control: no-cache
(aka. "end-to-end reload") doesn't revalidate and the server MUST NOT use a cached copy when responding.
What's going on!?
"jQuery probably copies those properties into the jQuery object." You're exactly correct, so it sounds like you already know! :)
Hopefully jQuery will update their code to stop touching that, but at the same time WebKit should have known better than to log a deprecation warning on an event (at least in my opinion). One mousemove handler and your console explodes. :)
Here's a recent jQuery ticket: http://bugs.jquery.com/ticket/10531
UPDATE: This is fixed now if you upgrade to jQuery 1.7.
Please note that if upgrading jQuery doesn't fix the issue for you it may have something to do with used extensions / plugins as Jake stated in his answer.
Best Answer
Normal reload
The same thing as pressing F5. This will use the cache but revalidate everything during page load, looking for "304 Not Modified" responses. If the browser can avoid re-downloading cached JavaScript files, images, text files, etc. then it will.
Hard reload
Don't use anything in the cache when making the request. (which is equal to SHIFT+F5 No need to open Developer console) Force the browser do re-download every JavaScript file, image, text file, etc.
Empty Cache and Hard Reload
Obviously, if the cache is empty then it will have to do a hard reload. This will again force the browser to re-download everything. However, if the page makes any after-the-fact downloads via JavaScript that weren't part of page load, then these might still use the cache, which is where emptying the cache helps because it makes sure that even these won't use cached files.
Note: This feature is only available when the developer tools are open.