1882903 - MouseEvent offsetX, offsetY return 0 value when accessed outside of event handler stack

Status: RESOLVED DUPLICATE of bug 1359440

(Core :: DOM: Events, defect)

Description

[Stephen [:st3v0]]

Steps to reproduce:

I debounced the mouse event to avoid reflows. And tried to access the offsetX property from the debounced event.
This doc (https://gist.github.com/paulirish/5d52fb081b3570c81e3a) states that offsetX/Y can trigger a reflow.

I've created a codesandbox example to demonstrate the issue:
https://codesandbox.io/p/sandbox/dreamy-sun-xrspkl

Demo: https://xrspkl.csb.app/

Just run the demo in both chrome/firefox and notice that the offset values always return 0 in firefox only.

Actual results:

The mouse event offset values always return 0 in firefox only, when accessed from a deferred callback.

Expected results:

I would expect the offset values to be non-zero and accurately reflect the the current offset x/y. I would also expect it to behave the same across all browsers, currently this is only broken in firefox; chrome, safari & edge all work the same.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::DOM: Events' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Hsin-Yi Tsai (she/her) [:hsinyi]]

What is the expected behavior per spec?