Bug 76607 – event.preventedDefault is not reset after an event is dispatched

• Component: UI Events
• Status: RESOLVED WONTFIX

[Pablo Flouret]

DOM Level 3 Events sez:

[[
As the final step of the event dispatch, for reasons of backwards compatibility, the implementation must reset the event object's internal-propagation and default-action-prevention states. This ensures that an event object may be properly dispatched multiple times while also allowing to prevent the event object's propagation or default actions prior to the event dispatch.
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[Pablo Flouret]

Created attachment 123081 [details]
patch

[Alexey Proskuryakov]

Does the new behavior match other browsers, or only the spec?

[Pablo Flouret]

(In reply to comment #2)
> Does the new behavior match other browsers, or only the spec?

Matches IE, not firefox or opera, so yeah, might be a better idea to hold off on this one and see if anyone else is going to match the spec as well.

[Alexey Proskuryakov]

I wonder where the "backwards compatibility" part comes from then. Maybe you'd be willing to search working group archives, or even e-mail them?

[Pablo Flouret]

There's some info on that here:
http://lists.w3.org/Archives/Public/www-dom/2011JanMar/0063.html

It seems that the wording didn't just confuse me.

I'd say it's mostly an unresolved issue, at least for the dom level 3 spec, dom core says that the flags should be reset in initEvent.

[Ryosuke Niwa]

Comment on attachment 123081 [details]
patch

View in context: https://bugs.webkit.org/attachment.cgi?id=123081&action=review

> Source/WebCore/dom/EventDispatcher.cpp:393
> +    return !defaultPrevented;

We normally return defaultPrevented, instead of !defaultPrevented, so you might want to do that here.

[Ryosuke Niwa]

It appears that DOM4 doesn't have that clause so it's likely that we don't need to fix this bug:
http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#dispatching-events

[Ehsan Akhgari [:ehsan]]

I think we can implement this in Gecko as well, as the webcompat risk seems rather low.  I filed this bug for Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=722437

[Ryosuke Niwa]

smaug from Mozilla told me IE started this behavior in 9. So I'll be shocked if this had a backward compatibility issue. On the other hand, I don't think this will cause a serious compatibility with us either so I'm fine with going forward with this patch as well.

[Pablo Flouret]

(In reply to comment #7)
> It appears that DOM4 doesn't have that clause so it's likely that we don't need to fix this bug:
> http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#dispatching-events

It was moved to initEvent(), see step 3 here: http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#dom-event-initevent

I think the idea is to make events re-usable, i can make a new patch if we want to go that way as well.

[Pablo Flouret]

Filed a new patch at bug 83964 with what the spec actually says now. This one should probably be closed as invalid.

[Ryosuke Niwa]

Comment on attachment 123081 [details]
patch

The spec has been changed NOT to reset these changes when re-dispatching events.

[Ryosuke Niwa]

Won't fix since this behavior is no longer mandated by the spec, and may pose backward compatibility issues.