1454525 - Touch event listener demo won't scroll in Firefox until you release the first touch

Status: RESOLVED INVALID

(Core :: DOM: Events, defect, P3)

Description

[Chris Peterson [:cpeterson]]

@ Olli: Is this a bug in our passive touch listeners or a bug in the CodePen demo?

STR:
1. Set "dom.event.default_to_passive_touch_listeners" pref to true.
2. Load https://codepen.io/alexreardon/pen/yKEKby
3. On a touch screen, press down on the blue frame with the "Can you use event.preventDefault() inside a dynamic event handler? Press your device and move to test" message.
4. While still pressing down, try to drag the frame up and down.

RESULT:
Nothing happens. The frame or text do not move in Firefox like they do in Chrome.

If you release the press and press down again, then you can drag the frame up and down as expected. This test requires addEventListener support for passive and `once` event listeners, but I see the same Firefox behavior whether the "dom.event.default_to_passive_touch_listeners" pref is true or false.

I see the same console log messages in both Firefox and Chrome:

> touchstart fired
> touchend fired
> was event prevented? true

Note that "touchend fired" is a test typo. It should read "touchmove fired".

Comment 1

[Chris Peterson [:cpeterson]]

I can still reproduce this bug in Firefox 66. The "dom.event.default_to_passive_touch_listeners" pref is now true by default in Firefox 61 (bug 1454107), so this test's dragging problem is now the default behavior in Firefox.

Comment 2

[Olli Pettay [:smaug][[e-mail]](vacation until Nov 16)]

I don't understand this. The test explicitly doesn't use passive listeners.

Comment 3

[Chris Peterson [:cpeterson]]

(In reply to Olli Pettay [:smaug] (massive needinfo queue, ping on IRC on anything urgent) from comment #2)

I don't understand this. The test explicitly doesn't use passive listeners.

Oops. I'm not sure how I missed the passive: false option. I don't recall where I found this CodePen test case.

However, with passive: false, I do still see Firefox and Chrome behave differently on my Windows touchscreen laptop as described in comment 0:

1. On the first touchstart, Chrome and Firefox both change the "Press your device and move to test" message to "yeah! 🤘", but only Chrome will allow you to scroll the page while dragging on this first touch.
2. If you touchend and then touchstart a second time, then Firefox will allow you to scroll the page by dragging.

Is this difference in behavior expected?

Comment 4

[Olli Pettay [:smaug][[e-mail]](vacation until Nov 16)]

Chrome's behavior looks broken to me.

Comment 5

[Olli Pettay [:smaug][[e-mail]](vacation until Nov 16)]

And are you using a Chrome version which actually dispatches touch events :)

Comment 6

[Chris Peterson [:cpeterson]]

(In reply to Olli Pettay [:smaug] (massive needinfo queue, ping on IRC on anything urgent) from comment #5)

And are you using a Chrome version which actually dispatches touch events :)

I think so. The CodePen test listens for touchstart and touchmove events. It responds to my Windows touchscreen in Chrome and Firefox, but not to my trackpad clicks.

https://codepen.io/alexreardon/pen/yKEKby