fix(eventPool): check existance of handler in EventTarget._unlisten

[mhagmajer]

Fixes #2120

[mhagmajer]

Failing check seems like false negative

[layershifter]

@levithomason I've marked this as ready for review, however I'm not sure that this is fixes something. We don't have reproduction and I don't see how this can be covered by unit tests.

[codecov-io]

Codecov Report

Merging #2246 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2246   +/-   ##
=======================================
  Coverage   99.73%   99.73%           
=======================================
  Files         151      151           
  Lines        2624     2624           
=======================================
  Hits         2617     2617           
  Misses          7        7

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5841dd7...d65569d. Read the comment docs.

[levithomason]

As I've shown here #2120 (comment), both our code and the browser's native code already gracefully handle removing undefined handlers. I want to get a broken test case that this fixes before merging.

[levithomason]

I should note, I spent 20-30 minutes researching and also trying to reproduce this. I could not do so in Chrome nor PhantomJS no matter what abuse I threw at our EventTarget and eventStack. I was also unabled to reproduce this in Chrome with removeEventListener.

The closest I could find was this angular/zone.js#21 issue. They had this error, but they also seemed unable to reproduce it. It seemed to resolve itself, unfortunately.

Lastly, neither _bound nor bound are properties that occur in our codebase. This leads me to believe the error is something native to the browser, or some other conflicting lib.

[levithomason]

Any more progress on this one?

[mhagmajer]

Not yet, I'll get back to you when I have something

…

On Sun, Nov 5, 2017, 00:47 Levi Thomason ***@***.***> wrote: Any more progress on this one? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#2246 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACmsIqp-_Npy3uihJ_39_tCZeEUaQSzHks5szPd-gaJpZM4QEIMT> .

[layershifter]

Closing for housekeeping. Will be reopened if we will have a repro case.