Bug 144309 – Web Inspector: Exception under ObjectTreeView.js on specific code.tutsplus.com page

• Status: RESOLVED
• Resolution: FIXED
• Component: Web Inspector

[Timothy Hatcher]

Load http://code.tutsplus.com/tutorials/say-hello-to-webkit-filters--net-23318 with the Inspector open. Didn't do anything special.

TypeError: null is not an object (evaluating 'a.match(chunk)')
comparePropertyDescriptors@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Views/ObjectTreeView.js:134:29
sort@[native code]
_updateProperties@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Views/ObjectTreeView.js:287:24
_updateChildren@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Views/ObjectTreeView.js:257:21
_updateChildren@[native code]
_getPropertyDescriptorsResolver@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Protocol/RemoteObject.js:510:17
_getPropertyDescriptorsResolver@[native code]
_dispatchCallback@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Protocol/InspectorBackend.js:181:31
dispatch@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Protocol/InspectorBackend.js:86:35
dispatchNextQueuedMessageFromBackend@file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Protocol/MessageDispatcher.js:42:34
file:///Users/Timothy/Work/Safari-TOT.git/OpenSource/WebKitBuild/Release/WebInspectorUI.framework/Resources/Controllers/FormatterContentBuilder.js:156:23: CONSOLE ERROR

[Radar WebKit Bug Importer]

<rdar://problem/20721693>

[Joseph Pecoraro]

I don't understand how this is possible.

Here is the code, annotated with some comments.

        ...

        // By this point, a and b should be strings. If they aren't something else went wrong in surrounding code.

        // 1. Rule out equivalent names.
        if (a === b)
            return 0;

        while (diff === 0) {

            // 2. Rule out one being shorter then the other.
            if (!a && b)
                return -1;
            if (!b && a)
                return 1;

            chunka = a.match(chunk)[0];
            chunkb = b.match(chunk)[0];
            anum = !isNaN(chunka);
            bnum = !isNaN(chunkb);

            // 3. Number versus non number cases.
            if (anum && !bnum)
                return -1;
            if (bnum && !anum)
                return 1;

            // 4. Number differences, if the same we continue.
            if (anum && bnum) {
                diff = chunka - chunkb;
                if (diff === 0 && chunka.length !== chunkb.length) {
                    if (!+chunka && !+chunkb) // chunks are strings of all 0s (special case)
                        return chunka.length - chunkb.length;
                    else
                        return chunkb.length - chunka.length;
                }
            }
            
            // 5. Different strings
            else if (chunka !== chunkb)
                return (chunka < chunkb) ? -1 : 1;

            // 6. Proceed to the next part of the string.
            a = a.substring(chunka.length);
            b = b.substring(chunkb.length);

        }

        ...


For us to have encountered a.match(chunk) and have "a" be null then, I think something must have gone wrong.

I believe Geoff just re-wrote Array.prototype.sort, so maybe that is related?

[Joseph Pecoraro]

Tim, it looks like Geoff's sort changes (r183288) got rolled out a bit later (r183308). My ToT (r183442) was not encountering the issue. Do you know what r### your JavaScriptCore was?

[Timothy Hatcher]

I had Geoff's change at the time. Rebuilding to see if it is better.

[Timothy Hatcher]

Looks fine now.

[Geoffrey Garen]

I see this in TOT, and in 183568, just before the Array.prototype.sort patch re-landed: 

Uncaught exception in inspector page while handling event Network.responseReceived:  (2)
TypeError: undefined is not an object (evaluating 'b.resource.type')
"[e-mail]:6957:63
[e-mail]:6968:114
[e-mail]:516:107
[e-mail]:535:96
[e-mail]:6825:240
[e-mail]:6238:130
[e-mail]:6992:112
[e-mail]:100:158
[e-mail]:102:9
[e-mail]:3576:30
[e-mail]:14444:51
[e-mail]:797:69
[e-mail]:723:34
[e-mail]:687:55
[e-mail]:651:20
[e-mail]:786:32"
_dispatchEventMain.js:687:105
dispatchMain.js:651
dispatchNextQueuedMessageFromBackend

[Timothy Hatcher]

Geoff, was that loading the same page linked above?

[Geoffrey Garen]

(In reply to comment #7)
> Geoff, was that loading the same page linked above?

Yeah, same page.

[Timothy Hatcher]

Seems to be fine.(In reply to comment #8)
> (In reply to comment #7)
> > Geoff, was that loading the same page linked above?
> 
> Yeah, same page.

Filed new bug about that. Bug 147451.