A note about synchronous xmlhttp requests and Firefox

By Chris on Jun 5, 2007 | In Development & Design, Scripting, Bugs, "Features" & Things Not Right | 6 feedbacks »

Since I just spent the better part of Friday debugging this problem and then the better part of Friday night Googling for a work around, it's worth noting that there is a "bug" in the Firefox implimentation of the xmlHTTPRequest object when using it for synchronous calls (i.e. the rest of the script pauses and waits for the request to complete, unlike typical asynchronous AJAX calls). When using the xmlhttp object in a synchronous fashion, Firefox does not process the onreadystatechange handler. Thus, any libraries that are dependant on this (for running post processing functions for example) will fail to work under these conditions. Interestingly, having the Firebug extension installed causes the object to behave properly. So a secondary note is to always test your apps in a "clean" instance of Firefox.

Here are the details that I came across, along with a work around: Lukav’s Weblog » Blog Archive » Firefox firebug and synchronos calls problem.

I've also set up a set of tests to demonstrate the problem. Try in both Firefox and IE to see the differences.

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Comment from: Ritesh [Visitor] Email
yep :( even I am stuck with same issue not sure how to get the synchronous work with firefox. chris did you find a break thru ?
08/13/07 @ 08:34
Comment from: Neil [Visitor] Email · http://www.hencam.co.uk
Easiest way is to move to asynchronous calls :roll:

Not a brilliant solution I know!
04/16/08 @ 11:01
Comment from: Otto [Visitor] Email
but i need the syncronous call:no:
04/21/08 @ 13:08
Comment from: Chris [Member] Email
Here's the snippet of code that was giving me trouble.

http://snippets.dzone.com/posts/show/5416

It's an XHR request object based on the work of Brad Fults (http://xkr.us/code/javascript/XHConn/) with the patch mentioned above applied. For Brad's sake and mine, please keep all comments intact if you use this in your own applications.
04/21/08 @ 13:39
Comment from: Dharmesh [Visitor] Email
Great blog. Really saved me a lot of time debugging.


:D
05/06/08 @ 12:18
Comment from: javaeedeveloper [Visitor]
Here is a workaround
https://bugzilla.mozilla.org/attachment.cgi?id=234988

See
https://bugzilla.mozilla.org/show_bug.cgi?id=313646#c9
07/05/08 @ 16:03

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