[Webkit-unassigned] [Bug 169789] I found one more onbeforeunload event return value coercion edge case

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=169789

--- Comment #2 from Chris Dumez <cdumez at apple.com> ---
(In reply to comment #1)
> (In reply to comment #0)
> > The newly-introduced test at
> > http://w3c-test.org/html/browsers/browsing-the-web/unloading-documents/
> > beforeunload-canceling.html named
> > 
> > > Returning false must not cancel the event, because it's coerced to the DOMString "false" which does not cancel CustomEvents: CustomEvent, cancelable
> > 
> > does not pass in Safari Tech Preview 25. Everything else does (except the
> > test "Returning a string must not cancel the event: BeforeUnloadEvent with
> > type "click", cancelable" which is fine since it's best if Safari doesn't
> > implement createEvent("beforeunload"); see
> > https://github.com/whatwg/dom/issues/362.)
> 
> I am not clear yet on what part of the spec says so.
> 
> I found:
> https://html.spec.whatwg.org/#the-event-handler-processing-algorithm (step 5)
> 
> which says:
> If return value is not null, then:
>     1. Set E's canceled flag.
>     ...
> 
> So if you return false, we cancel the event.

Oh, it is a CustomEvent, not a BeforeUnloadEvent. I get it now.

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