1688022 - Unship the `overflow`/`underflow` events

Status: RESOLVED FIXED

(Core :: Layout: Scrolling and Overflow, task)

Description

[Mats Palmgren (inactive)]

Given that these events are non-standard and not on track to become a standard I think we should unship them.
Chrome used to support a similar but incompatible overflowchanged event, but they removed it in ~2014 according to:
https://groups.google.com/a/chromium.org/g/blink-dev/c/1RCzsyEyNU8/m/5vNpxrhRbUIJ
(I checked a recent Chrome and it's still gone.)
That indicates to me that this functionality likely isn't needed by web developers.

FYI, the implementation of these events in Gecko have a history of causing crashes and security issues so we really want to remove them in their current form.

We use these events internally to implement a poly-fill for text-overflow:fade though:
https://searchfox.org/mozilla-central/search?q=%5Btextoverflow&path=
so we need to keep them "ChromeOnly" for now, until we implement that CSS feature.

Comment 1

[Olli Pettay [:smaug][[e-mail]]]

I moved to layout, since it is layout code which is creating and dispatching these events. So most of the work would be layout related.

Comment 2

[Mats Palmgren (inactive)]

Olli, do you know if we have (content process) counters for these events by chance? Or if not, where I could add them?

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

You mean counters for event listeners for them?
We don't, but something like https://searchfox.org/mozilla-central/rev/8dae1cc76a6b45e05198bc0d5d4edb7bf1003265/dom/events/EventListenerManager.cpp#382-403 could be done.

Comment 4

[Mats Palmgren (inactive)]

The numbers for Release appears to be 0.05% for both counters so far:
https://glam.telemetry.mozilla.org/firefox/probe/use_counter2_onoverflow_document/explore?activeBuckets=%5B%22no%22%2C%22yes%22%5D&channel=release&timeHorizon=ALL
https://glam.telemetry.mozilla.org/firefox/probe/use_counter2_onunderflow_document/explore?activeBuckets=%5B%22no%22%2C%22yes%22%5D&channel=release&timeHorizon=ALL

Comment 5

[Simon Pieters [:zcorpan]]

GitHub code search: 1.1k files
https://github.com/search?q=addeventlistener%28%27overflow%27+OR+addeventlistener%28%27underflow%27+OR+addeventlistener%28%22overflow%22+OR+addeventlistener%28%22underflow%22&type=code

httparchive query on sample_data (10k pages) finds nothing. I could run it on the full dataset if needed (NI me if so).

Comment 6

[Henri]

The change made in Bug 1888737 cause Tree Style Tab addon to not be able to scroll anymore.
TST issue: https://github.com/piroor/treestyletab/issues/3554
Maybe other addons are affected as well?

Comment 7

[Gregory Pappas [:gregp]]

Please file a new bug for this issue.

Comment 8

[Gregory Pappas [:gregp]]

I guess this can be considered fixed now, the events were disabled in release a while ago (bug 1907460)