Intent to Implement: Treat Document Level Wheel/Mousewheel Event Listeners as Passive

[Sahel Sharifymoghaddam]

Contact emails sa...@chromium.org Explainer

explainer: https://github.com/sahel-sh/Document-level-passive-wheel-event-listeners/blob/master/Explainer.md

design doc: https://docs.google.com/document/d/1dLxnzyixmR9MeHXE75Uz2nIVA0PaEjN4W3V_-df0sYI/edit?ts=5b6ad2d9

Summary wheel/mousewheel event listeners that are registered on document level targets (window.document, window.document.body, or window) will be treated as passive if not specified otherwise and Calling preventDefault inside such listeners will be ignored. This is the wheel version of the scrolling intervention which is shipped in M56: https://developers.google.com/web/updates/2017/01/scrolling-intervention Motivation On Windows and Mac platforms scrolling by mouse wheel (and touchpad) accounts for more than 90% and 96% of scrolling respectively.

75% of the wheel event listeners added to a document level element do not specify passive option, in these cases the browser needs to wait for the event to get handled before it starts scrolling even though more than 98% of such listeners do not call preventDefault().

Interoperability risk Firefox: No public signals Edge: No public signals Safari: No public signals Web developers: No signals

I have not added a new issue to WICG/interventions, yet, but considering that Firefox and Safari have enabled the equivalent touch scroll intervention, I expect to see positive responses on this intervention as well.

Compatibility risk Less than 0.3% of the pages might be impacted negatively. These are the pages that have a document level wheel event listener that has not specified passive option but calls preventDefault(). Explicitly setting passive:false for such listeners resolves the issue. UKM use counts will be added to find such URLs and approach them as needed. Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)? Yes or no.

Yes OWP launch tracking bug https://crbug.com/626196 Link to entry on the Chrome Platform Status https://www.chromestatus.com/features/6662647093133312 Requesting approval to ship?

No

[Rick James MSFT]

What is the best way to report site regressions caused by this change?

Opened crbug.com/931466

[Emil A Eklund]

Filing a bug is the best way. I cc:ed the contact person.

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