[whatwg] Adding mouseenter and mouseleave events

Gareth Hay gazhay at gmail.com
Thu Mar 15 13:05:34 PDT 2007

I think I am clearly missing something.
If we take your example, a parent element and several child elements.

If you want to perform an action on mouseover of a child -> attach  
the event there and cancel bubble.
If you want to perform an action on parent mouseover -> attach to  
parent element and check the target of the event.

Maybe your use case requires something different, but I can't imagine  
that scenario.
It is not good programming to know that events bubble and not to  
check the target IMHO anyway.

As for redundancy, the keypress event can be distinct from keydown  
and keyup, in that kepress does not fire for meta-keys, but the other  
two do, in some browsers. (Although I do admit a consensus in  
implementation would be good here)

On 15 Mar 2007, at 19:51, Magnus Kristiansen wrote:

> On Thu, 15 Mar 2007 20:10:33 +0100, Gareth Hay <gazhay at gmail.com>  
> wrote:
>> I'm not so sure it is a workaround though.
>> If you know that the event will bubble, you can make your handler  
>> prevent bubbling.
>> I don't think we should be adding two new events to a spec, when  
>> the existing events can work in the way you want, albeit with a  
>> line more code. If we did, we'd be forever adding very specialized  
>> events.
> You don't seem to understand the situation. Imagine there's a  
> parent element and several child elements. Every time you mouse  
> over a child element, a mouseover event triggers (and mouseout on  
> the previous element). This event bubbles up until it reaches the  
> parent element. An event handler on the parent can only prevent the  
> events from bubbling event further (which is not relevant), not  
> from reaching itself.
> To prevent it using bubble cancelling you would have to attach  
> events stopping bubbling to every child element of the target. Not  
> only is this an unreliable way of doing it, it also interferes with  
> potential other elements which actually want bubbling. The other,  
> more practical workaround is to look at each incoming event and  
> check "did this one come bubbling up, or does it belong here".  
> However, workarounds do not solve the problem itself.
> With mouseenter/leave, there is no bubbling. There is no need to  
> attach handlers to arbitrary elements, and no need to manually  
> check each incoming event to see if it's bubbling or direct. These  
> events are linked to a significant enough use case. They are no  
> more redundant than existing events like click (mousedown+mouseup)  
> and keypress (keydown+keyup).
> -- 
> Magnus Kristiansen
> "Don't worry; the Universe IS out to get you."

More information about the whatwg mailing list