GeezerVison

it's weird that heldValue: any but target: object and unregisterToken: object. I know the proposal uses the terms 'value' and 'object' but I don't think they exactly match the type system's definitions. In particular, object means "non-primitive". Can you provide null, undefined, "foo", false or 3 for target or unregisterToken?

1. target must be an object, i.e. non-primitive type.
   Specification: https://tc39.es/proposal-weakrefs/#sec-weak-ref-target

   2. If Type(target) is not Object, throw a TypeError exception.

   V8 implementation behavior:

   $ node --harmony-weak-refs
   Welcome to Node.js v14.0.0.
   Type ".help" for more information.
   > new WeakRef(null)
   Uncaught TypeError: WeakRef: target must be an object
       at new WeakRef (<anonymous>)
   > new WeakRef(undefined)
   Uncaught TypeError: WeakRef: target must be an object
       at new WeakRef (<anonymous>)
   > new WeakRef(1)
   Uncaught TypeError: WeakRef: target must be an object
       at new WeakRef (<anonymous>)
   > new WeakRef("str")
   Uncaught TypeError: WeakRef: target must be an object
       at new WeakRef (<anonymous>)
   

2. unregisterToken must be an object (non-primitive type), or undefined.

   Specification: https://tc39.es/proposal-weakrefs/#sec-finalization-registry.prototype.register

   5. If Type(unregisterToken) is not Object,
      a. If unregisterToken is not undefined, throw a TypeError exception.
      b. Set unregisterToken to empty.

   V8 implementation behavior (please note that v8 in Node.js still uses old specification name FinalizationGroup instead of FinalizationRegistry):

   $ node --harmony-weak-refs
   > var fg = new FinalizationGroup(() => {})
   undefined
   > fg.register({}, null, null)
   Uncaught TypeError: unregisterToken ('null') must be an object
       at FinalizationGroup.register (<anonymous>)
   > fg.register({}, null, undefined)
   undefined
   > fg.register({}, null, 1)
   Uncaught TypeError: unregisterToken ('1') must be an object
       at FinalizationGroup.register (<anonymous>)
   > fg.register({}, null, 'a')
   Uncaught TypeError: unregisterToken ('a') must be an object
       at FinalizationGroup.register (<anonymous>)
   > fg.register({}, null, false)
   Uncaught TypeError: unregisterToken ('false') must be an object
       at FinalizationGroup.register (<anonymous>)
   

3. heldValue can have any type.

   Specification: https://tc39.es/proposal-weakrefs/#sec-finalization-registry.prototype.register
   V8 implementation behavior:

   $ node --harmony-weak-refs
   > var fg = new FinalizationGroup(() => {})
   undefined
   > fg.register({}, null)
   undefined
   > fg.register({}, false)
   undefined
   > fg.register({}, 1)
   undefined
   > fg.register({}, {})
   undefined
   

I'd suggest omitting cleanupSome from .d.ts, or otherwise somehow mark it as dispreferred/not tab-complete it. It's "normative optional" in the specification, it's currently under some debate, and it's not going to be part of what V8/Chrome ships initially. See whatwg/html#5446 for context.

If it's "normative optional" in the specification, it can be marked as optional in .d.ts. Anyway this declaration is available only under --lib esnext compiler flag, which means that it isn't stable. If in final stage of the proposal this method will be removed, corresponding TypeScript declaration should reflect this change before move to stable es2020 lib.

If Chrome's not going to ship with it initially, let's make this optional to start so that people have to prove that it's available before using it. (Only when strict: true of course.)

If Chrome's not going to ship with it initially, let's make this optional to start so that people have to prove that it's available before using it. (Only when strict: true of course.)

Hi, any chance to expedite this change?

Yes, it got lost in my email, but I think it's good to go after I re-run the github CI.

It’s invalid to call WeakRef with undefined:

I’m fixing this in #42274.