Event.target not set for mouseEnter/Leave w/o jQuery in IE11

[simonihmig]

While working on #17227, and having somehow figured out how to run the (ES5-transpiled, jQuery-less) tests in the browser (used /tests/index.html?ie=true&dist=prod&skipPackage=container%2Cember-testing%2C%40ember%2Fdebug&moduleId=4a92ac35&jquery=none), I found that a couple of tests are failing in IE11 due to Event.target being null when using the special handling of mouseEnter/Leave when jQuery is not used.

It's only those assertions for Event.target, the actual events get fired correctly. See here:

This brings up two questions:

1. why weren't these failing in CI? I guess the browserstack tests do not run the no-jquery tests, but not sure. @rwjblue can you confirm?

2. how to fix this? The event target is set here for the fake event used in the special handling of mouseEnter/Leave (introduced in [BUGFIX release] fix mouseEnter/Leave event delegation w/o jQuery #16999): https://github.com/emberjs/ember.js/blob/master/packages/%40ember/-internals/views/lib/system/event_dispatcher.js#L326
   It seems for IE11 this is a readonly, non-configurable property, so neither directly setting it nor using defineProperty() (as it is now) works for IE. And of course we cannot use a native Proxy. 🤔

[rwjblue]

why weren't these failing in CI? I guess the browserstack tests do not run the no-jquery tests, but not sure. @rwjblue can you confirm?

Yes, exactly. We only run IE11 with jQuery.

[pixelhandler]

@rwjblue would this be a fair statement, "Ember w/o jQuery is only supported on evergreen browsers, and Safari, so IE11 is must use jQuery" ?

[simonihmig]

FWIW, for one of our apps, we dropped jQuery long before we dropped IE11 support. And AFAIK the other tests run fine w/o jQuery (would need to be confirmed), only this rather edge-casey thing makes some problems...

[rwjblue]

I believe this is resolved, @simonihmig can you confirm and close if you agree?

[simonihmig]

I believe this is resolved, @simonihmig can you confirm and close if you agree?

@rwjblue I don't think so, unfortunately!

At least if you refer to #17227, which fixes that mouseEnter events are called on SVG nodes in IE11.

However this issue refers to the fact that mouseEnter events on any DOM element do not have a Event.target correctly set up for IE11. And I still have no idea how to fix this. 🤔

[locks]

Closing due to inactivity. Post-Octane we are also moving towards on for even handling, which should get a separate issue if there's any bug. Thanks for the discussion!