In my ASP.Net app, which is javascript and jQuery heavy, but also uses master pages and .Net Ajax pieces, I am consistently seeing on the status bar of IE 6 (and occasionally IE 7) the message "2 items remaining" or "15 items remaining" followed by "loading somegraphicsfile.png|gif ." This message never goes away and may or may not prevent some page functionality from running (it certainly seems to bog down, but I'm not positive).
I can cause this to happen 99% of the time by just refreshing an .aspx age, but the number of items and, sometimes, the file it mentions varies. Usually it is 2, 3, 12, 13, or 15.
I've Googled for answers and there are several suggestions or explanations. Some of them haven't worked for us, and others aren't practical for us to implement or try.
Here are some of the ideas/theories:
IE isn't caching images right, so it repeatedly asks for the same image if the image is repeated on the page and the server assumes that it should be cached locally since it's already served it in that page context. IE displays the images correctly, but sits and waits for a server response that never comes. Typically the file it says it is waiting on is repeated on the page.
The page is using PNG graphics with transparency. Indeed it is, but they are jQuery-UI Themeroller generated graphics which, according to the jQuery-UI folks, are IE safe. The jQuery-UI components are the only things using PNGs. All of our PNG references are in CSS, if that helps. I've changed some of the graphics from PNG to GIF, but it is just as likely to say it's waiting for somegraphicsfile.png as it is for somegraphicsfile.gif
Images are being specified in CSS and/or JavaScript but are on things that aren't currently being displayed (display: none items for example). This may be true, but if it is, then I would think preloading images would work, but so far, adding a preloader doesn't do any good.
IIS's caching policy is confusing the browser. If this is true, it is only Microsoft server SW having problems with Microsoft's browser (which doesn't surprise me at all). Unfortunately, I don't have much control over the IIS configuration that will be hosting the app.
Has anyone seen this and found a way to combat it? Particularly on ASP.Net apps with jQuery and jQuery-UI?
UPDATE
One other data point: on at least one of the pages, just commenting out the jQuery-UI Datepicker component setup causes the problem to go away, but I don't think (or at least I'm not sure) if that fixes all of the pages. If it does "fix" them, I'll have to swap out plug-ins because that functionality needs to be there. There doesn't seem to be any open issues against jQuery-UI on IE6/7 currently...
UPDATE 2
I checked the IIS settings and "enable content expiration" was not set on any of my folders. Unchecking that setting was a common suggestion for fixing this problem.
I have another, simpler, page that I can consistently create the error on. I'm using the jQuery-UI 1.6rc6 file (although I've also tried jQuery-UI 1.7.1 with the same results). The problem only occurs when I refresh the page that contains the jQuery-UI Datepicker. If I comment out the Datepicker setup, the problem goes away. Here are a few things I notice when I do this:
This page always says "(1 item remaining) Downloading picture http:///images/Calendar_scheduleHS.gif", but only when reloading.
When I look at HTTP logging, I see that it requests that image from the server every time it is dynamically turned on, without regard to caching.
All of the requests for that graphic are complete and return the graphic correctly. None are marked code 200 or 304 (indicating that the server is telling IE to use the cached version). Why it says waiting on that graphic when all of the requests have completed I have no idea.
There is a single other graphic on the page (one of the UI PNG files) that has a code 304 (Not Modified). On another page where I managed to log HTTP traffic with "2 items remaining", two different graphic files (both UI PNGs) had a 304 as well (but neither was the one listed as "Downloading".
This error is not innocuous - the page is not fully responsive. For example, if I click on one of the buttons which should execute a client-side action, the page refreshes.
Going away from the page and coming back does not produce the error.
I have moved the script and script references to the bottom of the content and this doesn't affect this problem. The script is still running in the $(document).ready() though (it's too hairy to divide out unless I absolutely have to).
FINAL UPDATE AND ANSWER
There were a lot of good answers and suggestions below, but none of them were exactly our problem. The closest one (and the one that led me to the solution) was the one about long running JavaScript, so I awarded the bounty there (I guess I could have answered it myself, but I'd rather reward info that leads to solutions).
Here was our solution: We had multiple jQueryUI datepickers that were created on the $(document).ready event in script included from the ASP.Net master page. On this client page, a local script's $(document).ready event had script that destroyed the datepickers under certain conditions. We had to use "destroy" because the previous version of datepicker had a problem with "disable". When we upgraded to the latest version of jQuery UI (1.7.1) and replaced the "destroy"s with "disable"s for the datepickers, the problem went away (or mostly went away - if you do things too fast while the page is loading, it is still possible to get the "n items remaining" status).
My theory as to what was happening goes like this:
The page content loads and has 12 or
so text boxes with the datepicker
class.
The master page script creates
datepickers on those text boxes.
IE queues up requests for each
calendar graphic independently
because IE doesn't know how to
properly cache dynamic image
requests.
Before the requests get processed,
the client area script destroys
those datepickers so the graphics
are no longer needed.
IE is left with some number of
orphaned requests that it doesn't
know what to do with.
