The documentation for this parameter says:
"Refer to the MouseEvent.initMouseEvent() method for a description of this parameter."
However MouseEvent.initMouseEvent does not have this parameter.
There should not be an initWheelEvent() method to begin with I think.
(In reply to comment #1)
> There should not be an initWheelEvent() method to begin with I think.
Implementers have noted that initWheelEvent is widely used <https://bugs.webkit.org/show_bug.cgi?id=68791>.
Assigning to myself to take action on these open bugs.
Duping this to Bug 15330 (which came first). They are the same issue. This will be fixed with the next update--I'll resolve it once I've pushed the changes to the server.
*** This bug has been marked as a duplicate of bug 15330 ***
Duped bug verified--same goes for this one.