Hi guys,

Ive got some ajax that loads data from a php file then puts that into a div.

Every 5 seconds this runs.

I have a problem where on some older browsers or after you press CTRL+F5 on a recent browser instead of it updating without any images reloading it reloads every image.

Even if they are the same image, It seems to load each one again and again without just using a local copy ( so it doesnt look like everything reloads )

Does anyone have any clue how to stop it from doing this and force it to use a local copy unless the user actually ctrl+f5.

ctrl+F5 is SUPPOSED to reload everything from the server.

And because it is loading via XMLHTTP (AJAX) rather than the BROWSER processing the request it will download everthing.

AJAX (javascript) knows nothing about the browser cache, so cannot "reload" what the browser has cached

AJAX (javascript) knows nothing about the browser cache, so cannot "reload" what the browser has cached

Are you sure Chris ?
Because, for me, it's still the browser that makes the request, and it should reuse it's cache if there is a local copy.

What can be the cause of this, though, is a specific configuration of the server.
Like, an "expire" header that is always set to now()-1, or an "etag" that is time based.

Those things can defeat a browser cache.

But for me Lynxus, the answer would be that if you don't manage the server where you make requests yourself, there is nothing you can do.
If the browser don't use the cache, then it means that the server sends headers telling the browser not to use cache, or that the cached version is expired.

It may just apply to IE of course, where the XMLHttp object is a separate entity (ActiveX) from the browser and uses it's own mechanisms to load elements into memory rather hooking into the browser functions.

Originally Posted by tripy

Are you sure Chris ?
Because, for me, it's still the browser that makes the request, and it should reuse it's cache if there is a local copy.

What can be the cause of this, though, is a specific configuration of the server.
Like, an "expire" header that is always set to now()-1, or an "etag" that is time based.

Those things can defeat a browser cache.

But for me Lynxus, the answer would be that if you don't manage the server where you make requests yourself, there is nothing you can do.
If the browser don't use the cache, then it means that the server sends headers telling the browser not to use cache, or that the cached version is expired.

I have full access to the server as its a dedicated box.

Its not really the CRTL+F5 thing thats annoying, its the fact that on some browsers its just seems to reload all images anyway each time the ajax request goes through and others it doesnt.

Maybe its just a new feature in newer browsers that dont make it do it.

Just seems strange where lets say i have 20 images ALL the same.
Image.png

however it loads them all seprately , So you can actually see each one being loaded.

I would of expected either NO loading as it should be cached.
Or at least ALL of them appear at the same time. Being the same image n all.

Quite odd tbh.

And the vrowser(s) exhibiting this behaviour is?

I would of expected either NO loading as it should be cached.
Or at least ALL of them appear at the same time. Being the same image n all.

Not necessarily HTML rendering doesn't work like that. Each of the images may have a different location in memory and or the cache. Simply being the same file on the server doesn't mean they will be same on the client machine.

How's your browser configured? Has it set aside an amount for cache? Does it rely on cache or is the content never cached and the page is downloaded every visit?

What are the server headers that are being sent?

The main ones you would want for AJAX would be Expires, Last-Modified and Cache-Control. There are others that may help too like ETags that was mentioned above.

Without knowing these things, it may not be an ajax issue, but you own configuration/setup.

Like most requests made, local cache is usually checked first before it downloads anything new and unless HTTP caching is configured correctly it will be hard to make AJAX read the cache.

What could fail though is if AJAX relies on the POST method, as POST requests are never cached. If the Expires is too short, or has expired will always get new content. If the request made is to a non-caching link, e.g. one that alters it's get request so the browser always believes it's a new page.

I know this may not solve your issue, but hopefully there's some insight as to way it's not working.


Cheers,


MC