lib: add weak event handlers

[benjamingr]

This is a first attempt at "weak listeners".

Still a draft since I have no idea how to test this :] Do we have any idea how to test WeakRefs? EDIT: added a test.

Also still playing with this - but I think this is generally very useful and I will move certain APIs to it.

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

[benjamingr]

The motivation for this is:

• Improve the retention of handlers if a signal argument if a signal is passed to addEventListener.
• Eventually migrate all (most?) the places that do addEventListener for abort.
• Upstream this as .follow (or a different solution) to the DOM specification so that users (and not just core) can use it.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35051/

[benjamingr]

@jasnell @addaleax any chance this could get a review :]?

[benjamingr]

I need to think about this more.

[benjamingr]

Re-applied the changes with weak event handlers based on the comment (using an object as the retainer key)

[benjamingr]

Pinging @jasnell @addaleax @nodejs/events to make sure this doesn't land without a chance to object since the design changed (very so slightly though)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35935/

[aduh95]

Do you plan to add documentation for this feature?

[benjamingr]

@aduh95

Do you plan to add documentation for this feature?

Not really since this feature is internal to core - users cannot create weak listeners. This is because that is a spec requirement (we cannot add things to the standard EventTarget).

In the future - I'd like to use the mechanics of this in several utilities (and internally) namely:

• In new AbortController(...signals) (or .follow) which is being worked on in whatwg/dom
• In aborted (or a similar utility, see Add a utility for knowing an AbortSignal was aborted #37220 )

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35941/

[benjamingr]

@jasnell @addaleax @aduh95 I would really prefer not to land this without a review of the latest changes ^^

A review would be appreciated (the main change I want a LGTM on is passing a retainer object and not a boolean since that didn't work)

[benjamingr]

Landed in 5ef4c64 🎉