Hey Xiaocheng,
Thanks for working on improving interop! A few thoughts and questions below.
On 2/8/22 7:25 PM, Xiaocheng Hu wrote:
Contact emails
xiaoche...@chromium.org
Explainer
None
Specification
None. Not a standard feature.
Summary
Event.path is a non-standard API that returns the event's path, which
is an array of the objects on which listeners will be invoked. It is
supported by Blink only, causing web compatibility issues. Web
developers should switch to the equivalent standard API
Event.composedPath(), which returns the same result.
Blink component
Blink>DOM
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3EDOM>
TAG review
TAG review status
Not applicable
Risks
Interoperability and Compatibility
The removal of this API should improve interoperability, as it's
supported by Blink only. It still has 18% usage as of Feb 2022
(https://chromestatus.com/metrics/feature/timeline/popularity/345), so
we will only deprecate it for now, and will not remove it before the
usage drops low enough. We expect low compatibility risks, since there
is an equivalent standard API (Event.composedPath()) by all browsers,
and the following polyfill should also keep existing sites functioning
with minimum changes:
18% is a _lot_ of usage. So much that I'm surprised there aren't dozens
of compat bugs reported against Firefox. In
https://bugzilla.mozilla.org/show_bug.cgi?id=1697590#c0 there are only 2
linked site bugs. And there's only 3 in
https://github.com/webcompat/web-bugs/issues?q=is%3Aissue+composedPath
(the last one being from 2019).
I wonder how much of that 18% is feature detection and fallback
codepaths
<https://github.com/search?l=JavaScript&q=composedPath+event.path&type=Code>.
Are we aware of bug reports from Apple caused by event.path? I'm not
able to find any on bugs.webkit.org, but I could be doing it wrong.
Have you thought of ways to measure when event.path is called, and
event.composedPath isn't (not sure if that's even possible)? Maybe that
would show it's actually safe to remove.
if (!Event.prototype.path) { Object.defineProperty(Event.prototype,
'path', { get() { return this.composedPath(); } }); }
Given how simple this appears to be, I wonder if a better approach would
be to ask Mozilla and Apple if they would be willing to accept patches
to make event.path a legacy alias to event.composedPath - and then we
can spec it in DOM or Compat. The alternative is to send deprecation
messages for possibly a very long time, which doesn't really improve the
compat situation for a very long time. Or, we can figure out how to
measure the actual non-fallback usage of event.path and go from there.
Gecko: No signal Firefox does not support Event.path
WebKit: No signal Safari does not support Event.path
Web developers: Positive
(https://github.com/web-platform-tests/interop-2022/issues/26)
That should probably be counted as positive support from Mozilla, rather
than webdev support (no offense to James).
Other signals:
Debuggability
Usage of this deprecated feature will be reported to the DevTools
Issues Tab.
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/master/docs/testing/web_platform_tests.md>?
No
Flag name
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1277431
Estimated milestones
No milestones specified
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5726124632965120
This intent message was generated by Chrome Platform Status
<https://chromestatus.com/>.
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