1642147 - preventDefault does not work for unhandledrejection event

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect, P3)

Description

[Tom S. (please needinfo tschuster)]

It seems like the code add for dispatching unhandledrejection events intentionally ignores preventDefault and will always trigger a error message in the console: https://searchfox.org/mozilla-central/rev/d9d492eda787a6eda66016e6f8398ee759f7bc25/xpcom/base/CycleCollectedJSContext.cpp#709-710

Chrome will however prevent logging when preventDefault() is called in the event handler.

Comment 1

[Edgar Chen [:edgar]]

Attachment: test.html

Comment 2

[Edgar Chen [:edgar]]

The error message in the console is from https://searchfox.org/mozilla-central/rev/0e09b9191c02097034e46b193930f91c45b7885d/dom/promise/PromiseDebugging.cpp#277 and suppress if onLeftUncaught callback of UncaughtRejectionObserver returns true. Right now UncaughtRejectionObserver is handled independently with the unhandled event, there is no easy way to suppress the error from event.preventDefault(). However, I could try to handle them together if possible, but after my other works.

Comment 3

[Edgar Chen [:edgar]]

Won't work on this in a short time.

Comment 4

[valentin.lab]

can reproduce behavior on 112.0.2. This break MDN's description:

Many environments (such as Node.js) report unhandled promise rejections to the console by default. You can prevent that from happening by adding a handler for unhandledrejection events that—in addition to any other tasks you wish to perform—calls preventDefault() to cancel the event, preventing it from bubbling up to be handled by the runtime's logging code.

And Chrome handles this correctly (as described by MDN).

Comment 5

[brunoc]

I am on mac with firefox 124.0.2.
The bug is still reproductible. Any progress on this issue ?
Is there a workaround to this ?
I am using the unhandledrejection event to call preventDefault() on controlled exceptions. Still logging in the console

Comment 6

[CoolCmd]

From https://html.spec.whatwg.org/multipage/webappapis.html#unhandled-promise-rejections:

This algorithm results in promise rejections being marked as handled or not handled. These concepts parallel handled and not handled script errors. If a rejection is still not handled after this, then the rejection may be reported to a developer console.

Firefox ignores the standard and sends spam to the console.

Comment 7

[xmo]

Beyond the console spam which is annoying, this actively hinders automated testing: generally if an error bubbles up to the console / test runner it's a failure, here if the system makes use of preventDefault (generally specifically to test error paths) the test will fail on firefox, and requires significant alterations to the behaviour of the runner in order to work around the lack of a behaviour mozilla itself documents.

Comment 8

[Sławomir Osoba]

I kindly ask you to consider this mistake in 2025.

Comment 9

[Sławomir Osoba]

I renew my request in 2026

Comment 10

[Jan Jaeschke [:jjaschke]]

Attachment: Bug 1642147 - Respect preventDefault() on unhandledrejection for console reporting. r=edgar!

Comment 11

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/19e891e863bd
https://hg.mozilla.org/integration/autoland/rev/017ded32d9d5
Respect preventDefault() on unhandledrejection for console reporting. r=edgar

Comment 12

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/22142cab1d26
https://hg.mozilla.org/integration/autoland/rev/57b47548f41f
Revert "Bug 1642147 - Respect preventDefault() on unhandledrejection for console reporting. r=edgar" for causing devtools failures in browser_jsterm_await_error.js.

Comment 13

[Serban Stanca [:SerbanS]]

Reverted this because it was causing devtools failures in browser_jsterm_await_error.js.

• Revert link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | devtools/client/webconsole/test/browser/browser_jsterm_await_error.js | Test timed out

Comment 14

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/61eca2a337a9
https://hg.mozilla.org/integration/autoland/rev/0ad1c0949922
Respect preventDefault() on unhandledrejection for console reporting. r=edgar

Comment 15

[Jan Jaeschke [:jjaschke]]

Sorry for keeping you waiting for so long. I hope this works, if it doesn't please feel free to file a new bug and needinfo me. :)

Comment 16

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/0ad1c0949922