Consider "new.target" for constructor callbacks

[jasongin]

Reference nodejs/node#11975 (comment), nodejs/node#9293, nodejs/node#10915

In mixed JS/native inheritance scenarios, it can be necessary to get the "new target" for the constructor, via v8::FunctionCallbackInfo<T>::NewTarget(). In N-API this would be exposed as napi_get_cb_new_target() or something similar.

[boingoing]

Should this be added as an optional out parameter to napi_get_cb_info? If we remove the other methods in this family since one method could handle all of their use cases, it seems to make sense. Would make sense to do that together with #196.

[jasongin]

@boingoing I don't think it should be added to napi_get_cb_info() because it would be very rarely needed, only by some constructors. Maybe it could be combined with napi_is_construct_call() into a napi_get_cb_construct_info() or something like that.

[boingoing]

Maybe it could be combined with napi_is_construct_call() into a napi_get_cb_construct_info() or something like that.

This sounds like a good plan to me. Only constructors would be interested in this flag or new.target generally.

[jasongin]

Actually a callback is a constructor call if and only if a new target is defined. So I think we can just change napi_is_construct_call() to napi_get_new_target().

[mhdawson]

That makes sense to me.

[sampsongao]

nodejs/node#14698

[mhdawson]

Looks like related PR landed, closing.