70427 - Button in mouse events

Status: NEW

(Core :: DOM: Events, defect, P5)

Description

[Erik Arvidsson]

I've noticed that the event.button property does not return the correct value 
in the following mouse related events:

mouseover
mouseout
mousemove

This is not a bug according to the W3C Dom level 2 specs but it makes event 
handling soo much harder to do cerrectly. IE4+ supports the button property on 
all mouse related events and I think that makes sense.

The following is from the W3C spec:

button of type unsigned short, readonly 
During mouse events caused by the depression or release of a mouse button, 
button is used to indicate which mouse button changed state. The values for 
button range from zero to indicate the left button of the mouse, one to 
indicate the middle button if present, and two to indicate the right button. 
For mice configured for left handed use in which the button actions are 
reversed the values are instead read from right to left.

A good example where there might be problems without this property is in simple 
drag and drop scripts where the mouse button was released outside the element 
listening for the mouseup.

(I assigned this to Blake Ross since he is the one assigned to bug 60703 which 
is related to the button as well.)

Comment 1

[Blake Ross]

Do we want to do this?

Comment 2

[Taras Tielkes]

Erik, I think Mozilla has implemented event.button for a *loong* time.

Comment 3

[Taras Tielkes]

Erik, what's the difference between this one and 60703?

Both seem to cover incorrectly numbered mouse buttons.

Comment 4

[Erik Arvidsson]

The problem as I see it is that the button property gives garbage in non click 
realted mouse events. It should optionally be possible to tell what button is 
pressed in a mousemove event for exmaple.

There are however issues with how button is defined in the W3C specs. IE solved 
this in a much better way.

The following is taken from the MSDN

iWhichButton Integer that specifies or receives one of the following values:
0 Default. No button is pressed. 
1 Left button is pressed. 
2 Right button is pressed. 
3 Left and right buttons are both pressed. 
4 Middle button is pressed. 
5 Left and middle buttons both are pressed. 
6 Right and middle buttons are both pressed. 
7 All three buttons are pressed.


I don't see a solution for when multiple buttons are pressed that follows the 
W3C specs but when a sinlge button is pressed a good idea would be to return 
that value instead of the garbage value.

The best value (IMO) for no button pressed would be null (or possibly -1)


Bug 60703 was filed because the property was off by one for mousedown, up and 
click. This bug is for the non click related mouse events.

Comment 5

[Erik Arvidsson]

Attachment: This shows that the button property gives incorrect (garbage) value for mousemove events

Comment 6

[Taras Tielkes]

The next is just my opinion, of course:

1) Can you give a scenario where multiple simultaneous button clicks could be 
used. I know of no Win32 program that uses this. (Well, except Quake :-) )
2) I think the button value in non-click mouse events should be treated as 
garbage. It'a pity that the DOM mouse buttons don't start at 1 though.
3) In the example you give in your first comment, it would be easy to catch 
mouseout for the element.

Comment 7

[Blake Ross]

-> joki

Comment 8

[Madhur Bhatia]

QA contact updated

Comment 9

[Asa Dotzler [:asa]]

Bugs targeted at mozilla1.0 without the mozilla1.0 keyword moved to mozilla1.0.1 
(you can query for this string to delete spam or retrieve the list of bugs I've 
moved)

Comment 10

[Vladimir Ermakov]

this is dom events

Comment 11

[Mike Kaply [:mkaply]]

Can someone be more specific as to what I am supposed to notice in this testcase
please?

Or create a testcase that just shows the button issue?

Thanks

Comment 12

[Erik Arvidsson]

This seems to have changed a little since the last time I checked on this.

Now eventObject.button always return 0 when a non-click related event is fired.

To see this scroll the page down so you can see the object.button row. Now press
the mouse buttons and move the mouse around and you'll see that the button
property is always 0 (which means left button).

In a perfect world it would be possible to tell which buttons are pressed in a
mouse move event.

Comment 13

[Doron Rosenberg (IBM)]

mkaply: basically .button should tell us which mouse button(s) are pressed.  I
think most uses can be workarouned using existing event attributes though.

Comment 14

[Felipe]

mouseover et al still appear to return 0 in all cases, regardless of which
button is pressed or whether any button is pressed at all.

And since everyone agrees that Microsoft's solution is better here, perhaps add
a 'buttons' property to the MouseEvent object that uses Microsoft's model? (W3C
could adopt it for DOM3....)

Comment 15

[Firefox Bug Husbandry Bot]

https://bugzilla.mozilla.org/show_bug.cgi?id=1472046

Move all DOM bugs that haven’t been updated in more than 3 years and has no one currently assigned to P5.

If you have questions, please contact :mdaly.