events: Start porting WPT tests

[benjamingr]

I tried porting the WPT tests through git node wpt - it worked pretty well initially but there were several big issues:

• All the meaningful tests are HTML files.
• Even the JS files contained a lot of DOM logic.
• The WHATWG tests don't test EventTarget directly - rather they test document and window as event targets.

I started down the path of implementing a document, window, appendChild and then decided it would probably be easier to just manually port these tests after changing them to terms Node understands.

Ideally, we could contribute these back to WPT as less-tried-to-document tests for EventTarget.

For example where the test does document.addEventListener I do let document = new EventEmitter() first.

When I tried porting https://github.com/web-platform-tests/wpt/blob/master/dom/events/AddEventListenerOptions-once.html#L36-L57 it threw ERR_EVENT_RECURSION indicating that that behavior is probably not spec compliant. @jasnell any objections to changing it to align with the spec and allow dispatching an event while in an event handler for the same handler?

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[jasnell]

We had a similar issue when introducing the WHATWG URL parser which is why we have so many test-whatwg-url-* tests and don't rely so much on the WPT tests for those. I suspect we'll have to do the same.

When I tried porting web-platform-tests/wpt:dom/events/AddEventListenerOptions-once.html@master#L36-L57 it threw ERR_EVENT_RECURSION indicating that that behavior is probably not spec compliant. @jasnell any objections to changing it to align with the spec and allow dispatching an event while in an event handler for the same handler?

Yeah, I suspect we should actually file this as an issue with the EventTarget standard itself. The following test case actually crashes Chrome for me and Firefox throws with an error about too much recursion:

const et = new EventTarget();
et.addEventListener('foo', () => et.dispatchEvent(new Event('foo')));
et.dispatchEvent(new Event('foo'));

It's an obvious footgun that really shouldn't be allowed. Note that we currently have the same issue with EventEmitter in that we allow ee.on('foo', () => ee.emit('foo')) which throws a max call stack exceeded error. It's a deeper problem with EventTarget because the error is just pushed to uncaught error and does not necessarily stop the progression of the code in browsers. The ERR_EVENT_RECURSION may not be fully spec compliant here but it prevents these issues and should be kept.

[benjamingr]

@jasnell

. I suspect we'll have to do the same.

Roger, I'll start porting the whatwg tests that route. I'm also checking with the #whatwg people on IRC to see if they're interesting in upstreaming those tests (for example: tests directly testing EventTarget rather than document)

I think I fixed the root cause for the recursion issue in #33624 - it's fine to dispatch events from events with the same type as long as they're not the same isntance.

If you'd like we can add a "max call depth" or similar check though I would rather not and have the user just reach "Maximum call stack exceeded" like any other non-event-related recusion and like browsers do.

I'll add a "WIP" to the title in the meantime (at least until #33624 and some other fixes land).

[benjamingr]

@jasnell any feelings regarding just porting all the WPTs in one PR (with a pass/fail status, a bunch failing) rather than make a lot of smaller changes?

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/34053/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/34087/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/34100/

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----------------------------------- PR info ------------------------------------
Title      events: Start porting WPT tests (#33621)
   ⚠  Could not retrieve the email or name of the PR author's from user's GitHub profile!
Branch     benjamingr:event-target-wpt-start -> nodejs:master
Labels     events, eventtarget, test
Commits    1
 - events: port some wpt tests
Committers 1
 - Benjamin Gruenbaum 
PR-URL: https://github.com/nodejs/node/pull/33621
Reviewed-By: James M Snell 
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/33621
Reviewed-By: James M Snell 
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   ⚠  Commits were pushed since the last review:
   ⚠  - events: port some wpt tests
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   ℹ  This PR was created on Thu, 28 May 2020 17:18:14 GMT
   ✔  Approvals: 1
   ✔  - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/33621#pullrequestreview-421144116
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[benjamingr]

I'll land it manually

[benjamingr]

Landed in 2a1273c 🎉

[Ethan-Arrowood]

this creates conflicts with tests added in #34169