You cannot programmatically focus an element after removing its focus handler

[JoolsCaesar]

Description

I'm seeing this in the latest chromium browsers Windows Chrome & Edge 89, using jquery 3.6.

If you add and remove an element's focus handler, subsequent calls to $element.focus(), will do nothing.
HTML:

<div tabindex="-1" class="fdiv"></div>

CSS:

.fdiv{
  height:100px;
  width:100px;
  border:1px solid black;
}
.fdiv:focus{
  background-color:green;
}

See the linked to test case below. I have a simple div that turns green when you focus it and some js that will focus said div after 2 seconds.
Before setting this timeout I add and then immediately remove an empty focus handler:

//Using https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js

const $origDiv = $('.fdiv');

// Comment out the following line to fix
$origDiv.on('focus',function(){}).off('focus');

setTimeout(function(){
	$origDiv.focus();
},2000)

If you run the fiddle, the div should turn green (gain focus) after 2 seconds, but it doesn't!
If you comment out the focus handler line, all works as expected.

Link to test case

https://jsfiddle.net/JoolsCaesar/ut371acd/

---

^{EDIT by @mgol: I fixed syntax highlighting in code blocks.}

[JoolsCaesar]

FWIW I tracked this down to this bit in jquery:

function leverageNative( el, type, expectSync ) {

	// Missing expectSync indicates a trigger call, which must force setup through jQuery.event.add
	if ( !expectSync ) {
		if ( dataPriv.get( el, type ) === undefined ) {
			jQuery.event.add( el, type, returnTrue );
		}
		return;
	}

dataPriv.get( el, type ), where el is the element we're attempting to focus and type is 'focus', returns false, so we just drop out without doing anything.

[mgol]

Thanks for the report! The code you mentioned exists since jQuery 3.4.0, I suspect it only became a problem after #4813 landed.

[JoolsCaesar]

Makes sense. I spotted this after upgrading from 3.0.0 to 3.6.0, so couldn't narrow it down much.

[mgol]

I meant the bug is only reproducible in jQuery 3.6.0, it works fine in 3.5.1 despite the fact 3.5.1 contains the code you linked to. Hence, most likely it only causes the issue in connection with #4813 (although I haven't verified it yet).

[mgol]

PR: #4885