Alright, this is the last of the straightforward ones. The remaining ones: map, filter, take, drop, flatMap require creating a wrapping iterator AFAIS. Any pointers on how to go about it are most welcome! Perhaps we need a helper class a la async-from-sync iterator?

W.r.t. wrapping iterators: I imagine you add a new JS_CLASS_ITERATOR_HELPER and instantiate it with JS_NewObjectClass().

The class probably needs to be defined as such:

ctx->class[JS_CLASS_ITERATOR_HELPER] = JS_NewObjectProto(ctx, ctx->iterator_proto);

And have .next and .return methods that call the methods of the same name on the wrapped object (edit: and have mark and finalize callbacks.)

That's what I had in mind. Great, I'll try to give it a go this week!