1515953 - TypeError "class heritage customElements.get(...) is not an object or null" in mailWidgets.js during Thunderbird startup

Status: RESOLVED FIXED

(Thunderbird :: General, defect)

Description

[Stefan Sitter [:ssitter]]

During Thunderbird 66.0a1 (BuildID 20181221092739) startup the following error is reported in console:

> TypeError: class heritage customElements.get(...) is not an object or null
> mailWidgets.js:270:31 

The error is reported for class MozTreecolImage:
https://searchfox.org/comm-central/rev/ffaaa034245811ec92643f967733a39649f3b13c/mail/base/content/mailWidgets.js#270

Comment 1

[:aceman]

Yes, I also see this constantly. Started in TB 65.

Comment 2

[Arshad Khan [:arshad]]

This is a racing issue. The mailWidgets custom elements are being loaded before the firefox custom elements are loaded so there is an error when treecolimage tries to extend treecol(fx custom element).

Comment 3

[Arshad Khan [:arshad]]

Attachment: treecolimage-bug.patch

Comment 4

[Arshad Khan [:arshad]]

Attachment: treecolimage-bug.patch

using setElementCreationCb so that the class code is executed only when the treecol-image tag is encountered.. since this was a racing issue, this fixes the problem..

Comment 5

[Arshad Khan [:arshad]]

Attachment: treecolimage-bug.patch

Comment 6

[Magnus Melin [:mkmelin]]

In what way is it a racing issue?
If it's a racing issue, why would this make treecol-image work consistently? Of course it would remove the exception in the console for the cases where treecol isn't set yet, but for those cases, the treecol-image would not work, right?

Comment 7

[Arshad Khan [:arshad]]

(In reply to Magnus Melin [:mkmelin] from comment #6)

In what way is it a racing issue?
If it's a racing issue, why would this make treecol-image work consistently? Of course it would remove the exception in the console for the cases where treecol isn't set yet, but for those cases, the treecol-image would not work, right?

treecol-image is called a lot of times.. so for the first few times the treecol-image throws that exception/error but after sometime when treecol is available in scope, the further calls to get the custom element doesn't throw error/exeception.

IMO it is a racing issue in the way that the custom element code of TB is called earlier than FX's custom element code so the Tb custom element that depends/extends the fx's custom element will throw error/exception.

Comment 8

[Arshad Khan [:arshad]]

*treecol-image custom element definition is called many times, as the custom element code is attached to domWindowCreated event so maybe for the first few window creation event the fx custom elements are not loaded in scope but then later they are added to scope, I hope what I am sayin makes sense.

Comment 9

[:aceman]

Kinda like bug 1519653?

Comment 10

[Magnus Melin [:mkmelin]]

Why would there be more than one domWindowCreated event for a window?
I don't think the customElements.js is ever loaded more than once for a window.

Comment 11

[Arshad Khan [:arshad]]

(In reply to Magnus Melin [:mkmelin] from comment #10)

Why would there be more than one domWindowCreated event for a window?
I don't think the customElements.js is ever loaded more than once for a window.

the DOMWindowCreated is called on the creation of each window right?

Comment 12

[Magnus Melin [:mkmelin]]

Yes, but the loaded customElements are put (only) into the scope of the specific window, so shouldn't leak between windows.

Comment 13

[Arshad Khan [:arshad]]

(In reply to Magnus Melin [:mkmelin] from comment #12)

Yes, but the loaded customElements are put (only) into the scope of the specific window, so shouldn't leak between windows.
yes you are right.

Comment 14

[Magnus Melin [:mkmelin]]

Attachment: bug1515953_inherit_in_dummy.patch

Turns out the problem comes from loading the dummy document.

https://searchfox.org/comm-central/source/mozilla/toolkit/content/customElements.js#299

I don't know why that is loaded or what it's used for, but I'm pretty sure we don't need to load our elements into there.

Comment 15

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/comm-central/rev/bffe1c0bac89
don't load the Thunderbird custom elements in the dummy.xul document. r=arshad

Comment 16

[alta88]

I was hoping this might fix Bug 1517818, but it doesn't.