Turns out this was an artefact of a Firebug bug. The Ajax request was cancelled, but Firebug continued reporting it as active. Details here.
I have long running XMLHttpRequests and I need to be able to abort them under certain circumstances.
I set up the request in a normal way:
ajax = $.getJSON(url + "?updates", function(data) { ...; });
Later on I want to abort this request, seems straightforward:
ajax.abort();
When I look in Firebug however, I see it is still running...
I console.log out the value of ajax just before I try and abort it, it confirms that its value is and XMLHttpRequest (with a readyState of 0).
Are there restrictions on how and when abort() fires on an XMLHttpRequest?
Calling abort resets the object; the onreadystatechange event handler is removed, and readyState is changed to 0 (uninitialized).
i do not think it cancels the request itself, it just ignores any response (manipulating the event handler)- but i didnt really try it out yet.
but it will deifnitely allow you to reuse the object - no matter if the browser still has some thread working with the old request.
you may take a look at the JSONP-Plugin With this Plugin you have the ability to manually abort the request. Also take a look at "a cautionary note" at IBM's Technical library:
First and foremost, there is no error handling for JSONP calls. If the dynamic script insertion works, you get called; if not, nothing happens. It just fails silently. For example, you are not able to catch a 404 error from the server. Nor can you cancel or restart the request.
Another great article on handling this is found here: http://www.bennadel.com/blog/1500-Catching-Timeout-Errors-With-jQuery-Powered-AJAX.htm.
I simply converted my .getJSON request to .ajax and added the timeout/error handling.
Thanks!
take a look at the jquery AJAX Queue/Cache/Abort/Block Manager, maybe this can help you to prevent you current situation.
来源：https://stackoverflow.com/questions/1287971/aborting-a-jquery-getjson-xmlhttprequest