WeakMap support

[gabrielschulhof]

N-API can already create and manipulate a Array, but there is no support
to create and manipulate a WeakMap, which may sometimes be useful for
internally attaching extra data to arbitrary objects.

(You might be able to define your own finalizer callbacks also using a
WeakMap anyways, by giving a key for the object to check, and the value
being a external value with a finalizer callback defined, so that it will
be called when the key object is finalized; I don't know whether or not it
will work, but it seems like it is allowed to work, at least.)

[gabrielschulhof]

Re: nodejs/node#14256

[bnoordhuis]

but there is no support to create and manipulate a WeakMap

There's no support for that in the V8 C++ API either.

[gabrielschulhof]

There is always the roundabout way of obtaining the JS API using napi_get_global() and napi_get_named_property().

[bnoordhuis]

Sure, but why would you want to? At that point you're just adding API sugar.

[gabrielschulhof]

Oh, definitely. There's not even a performance benefit, since you're not saving yourself a trip into JS by using a native API, because, as you pointed out, the native API does not exist. Of course, other engines may have such an API, but I guess when we're faced with that, we can reconsider this issue. I guess we can close this issue.