[webkit-dev] mouseenter and mouseleave events

Maciej Stachowiak mjs at apple.com
Tue Apr 16 15:54:27 PDT 2013

On Apr 16, 2013, at 5:08 AM, Allan Sandfeld Jensen <kde at carewolf.com> wrote:

> Hi webkit-dev
> I have recently uploaded a new patch to 
> https://bugs.webkit.org/show_bug.cgi?id=18930 to implement mouseenter and 
> mouseleave events.
> These events are part of DOM3 http://www.w3.org/TR/DOM-Level-3-Events/#events-mouseevents and supported by MSIE, Mozilla and pre-blink Opera. They are also 
> listed as issues jQuery needs to work around in WebKit 
> https://bugs.webkit.org/show_bug.cgi?id=110007
> Previously they have not been implemented because they were not considered 
> important, and could cause performance regression by issuing more events on 
> every mouse-move that may not even be used by many websites.
> After I refactored hit-testing in the fall and especially moved the update of 
> hover/active state out of hit-testing, it is now possible to dispatch these 
> events where the hover state is updated, which makes the logic of dispatching 
> mouseenter and mouseleave events correctly simple. It is also possible to only 
> do one check for possible capturing listeners before issuing any mouseenter or 
> mouseleave events for a mousemove.
> This is what the new patch does. It does incur an additional overhead by 
> checking for the existence of capturing listeners, but the check is of lower 
> magnitude than existing iterations over the tree, and should keep performance 
> comparable, and is in all circumstances faster than issuing new events that 
> fall for deaf ears.
> Are there more objections for the support of mouseenter and mouseleave events 
> in WebKit?

Seems like a reasonable feature to add.

 - Maciej

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