1743735 - TouchEvent.targetTouches list saved on touchstart is empty on touchmove

Status: NEW

(Core :: DOM: UI Events & Focus Handling, defect)

Description

[Ksenia Berezina [:ksenia]]

Attachment: test.html

This was initially reported in https://github.com/webcompat/web-bugs/issues/94490 where it's impossible to "navigate" a canvas game by swiping on https://www.starbucks.co.jp/egift_holiday2021/find_gift_santa/

I've attached a reduced test case to replicate the behaviour, it's reproducible in RDM or a Firefox Android device.

The site is saving a reference to event.targetTouches on touchstart and accessing it on touchmove, however in Firefox at that point the list is empty, which causes an error. This is not happening in Chrome.

Comment 1

[Ksenia Berezina [:ksenia]]

I found another example similar to this on https://patrickhlauke.github.io/touch/touchlist-objects/ (on touch the green circle representing targetTouches becomes visible in Chrome, but not in Firefox).

Comment 2

[Henri Sivonen (:hsivonen) (away from Bugzilla likely until 2022-07-11)]

From the description, seems to meet the definition of S2. Edgar, please downgrade if this should be S3 instead.