Bug 218860 – Events delivered when all event listeners in the ancestor chain are passive should be cancelable=false

• Component: DOM
• Status: NEW

[Simon Fraser (smfr)]

Wheel/touch events delivered to passive event listeners should have their `cancelable` property set to false.

[Radar WebKit Bug Importer]

<rdar://problem/71334287>

[Simon Fraser (smfr)]

Note that Chrome does this, Gecko does not.

[Emilio Cobos Álvarez (:emilio)]

Should the cancelability of the event really depend on the listener? What do we do for other events, or if there are both passive and non-passive listeners?

[Chris Dumez]

https://w3c.github.io/touch-events/#cancelability

"""
In particular, a user agent may generate only uncancelable touch events when it observes that there are no non-passive listeners for the event.
"""

[Chris Dumez]

Corresponding spec for Wheel events:
https://w3c.github.io/uievents/#cancelability-of-wheel-events

[Simon Fraser (smfr)]

I filed https://github.com/w3c/uievents/issues/282 on clarifying this for wheel events.

[Simon Fraser (smfr)]

Looking at blink code, it appears (for touch events at least) to set the event to non-cancelable if all the event listeners in the ancestor chain of the target element have passive listeners. My testing suggests that the same is true for wheel event listeners.

[Ryosuke Niwa]

Changing the event type based on the type of event listeners seem very strange & weird.

[Simon Fraser (smfr)]

We'll do this now if the event starts in the passive event listener region.

[Ahmad Saleem]

Safari is failing quite a few tests:

https://wpt.fyi/results/dom/events/non-cancelable-when-passive?label=master&label=experimental&aligned&view=subtest&q=non-cancelable