650619 - FF4: javascript errors not reported in web console when they occur in async called function

Status: RESOLVED INVALID

(Core :: General, defect)

Description

[Paul]

User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0
Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0

When a piece of JS code causes an error, it is normally visible in the web console or error console. However, on FF4 when a function called asynchronously causes an error, it is not visible in the web console or error console. On FF3, javascript errors are shown as expected.

Code snippet from http://paultv.xs4all.nl/ff4/jspoc.html:

var request

function oops() {
    // The following line would give a message in the web console:
    //document.getElementById('doesnt_exist').innerHTML = 'oops'

    request = new XMLHttpRequest()
    request.onreadystatechange = listen
    request.open('POST', 'bogus')
    request.send('')
}

function listen() {
    // Set something to prove listen function is started
    document.getElementById('does_exist').innerHTML = request.readyState

    // The following line DOES NOT give a message in the web console,
    // but it DOES give a message in the FF3 error console
    document.getElementById('doesnt_exist').innerHTML = 'oops'
}


Reproducible: Always

Steps to Reproduce:
1. Create a web page on a webserver that creates a javascript error in an async called function, or use http://paultv.xs4all.nl/ff4/jspoc.html
2. Open web console
3. Go to the page

Actual Results:  
On FF4: no javascript errors are reported in the web console
On FF3: javascript errors are reported in the error console

Expected Results:  
FF4 should show all javascript errors, like FF3

Comment 1

[Paul]

The error console in FF4 doesn't show the errors either.

Comment 2

[Josh Matthews [:jdm]]

Paul, I ran that snippet on an FF4 nightly and it worked fine.  Can you reproduce on a nightly?  I filed a bug very similar to this one several months ago and it was fixed, so I think this is probably a dup.

http://nightly.mozilla.org/

Comment 3

[Josh Matthews [:jdm]]

Woah, this is weird.  The testcase you linked works fine in a debug build corresponding to the nightly, while the actual nightly does not.  Color me confused.

Comment 4

[Paul]

Josh, I'm downloading the nightly right now, but it's kinda slow. I'll let you know the results when I have it installed.

With a C/C++ project in the past, I've encountered a similar problem, in my case:
- I didn't explicitly initialize a certain var in the code
- The debug version initialized every local var when it was created automatically
- The optimized version didn't initialize vars anymore

Dunno if it might be something similar in this case.

Comment 5

[Paul]

Hmmm... I donwloaded the nightly (Mozilla/5.0 (Windows NT 6.1; rv:6.0a1) Gecko/20110417 Firefox/6.0a1), and that worked fine; I did get the JS errors in the web console there.

Comment 6

[Josh Matthews [:jdm]]

Hmm, I see the errors in a fresh profile, but not my main browsing one.  How peculiar.

Comment 7

[Paul]

Now this is funny... The one I downloaded first was a 32 bits version; works as expected. Just for fun and giggles I also tested the 64 bits nightly, and there I did not get the JS errors.

Comment 8

[Josh Matthews [:jdm]]

There's a bug worth investigating here, it appears.

Comment 9

[Paul]

It's the same case on the regular FF4 build: the 32 bits version shows the JS errors in the web console as expected, while the 64 bits version doesn't.

At least there's a workaround then :) It also limits the scope for the bug hunting significantly, I suppose.

Comment 10

[Paul]

It also makes me wonder if the debug versions behave the same... does your debug version happen to be 32 bits?

Comment 11

[Josh Matthews [:jdm]]

All of my tests are on 32 bits, so that's not the cause here.

Comment 12

[Paul]

Goody. I did a fresh FF4 on another Windows 7 64 bits machine, and there I do get the JS error messages. The other machine has far less software installed (e.g. no virus scanner), and on the original machine it was a FF 3->4 upgrade at some time though... I'll continue testing with yet another W7 64 bits machine that has an FF 3->4 upgrade.

Comment 13

[Paul]

Since I couldn't reproduce the issue on another machine, I started testing with FF on my main machine. As soon as I created a clean profile, I got the JS errors in the web console. Given your test results (test vs main profile), this may be kinda significant.

Comment 14

[Paul]

Nice, I do have it reproduced on another machine as well. The only difference between the working and non-working situation is that I installed the Windows Malicious Software Removal Tool of April 2011, and rebooted the machine.

Comment 15

[Paul]

Creating a new profile also helped on the machine where I reproduced the problem. Comparing the profiles gives a lot of differences on both machines, because of the add-ons installed on them.

I haven't managed to reproduce it yet on a cleaner FF4 install, to make comparing the profiles easier. I can't spend much more time on testing this today.

Since we have seen this on 3 separate installations already between two people, it's more than an incident, so I think it's worth investigating further.

Comment 16

[Paul]

This situation turns out to be caused by AdBlock Plus.

- In FF3, with ABP active, the JS errors are displayed
- In FF4, without ABP active (fully disabled or not installed), the JS errors are reported
- In FF4, with ABP active, the JS errors caused by async called JS functions are not reported anymore

Since this is an ABP problem, and not a core problem, I'll close the bug report as resolved/invalid, and create a bug report on the ABP site.

Comment 17

[Wladimir Palant]

Note: I ended up filing bug 653533 on this, this *is* a core problem.