context.cc

NAN_METHOD(Context::createEvent) {
  NanScope();

  Local<Object> obj = NanNew<Object>();
  NanSetInternalFieldPointer(obj, 1, Context::get());
  Handle<Value> argv[1] = { obj };

  // Handle<Value> argv[1] = { NanNew<External>((void *) Context::get()) };
  NanReturnValue(NanNew(Event::constructor)->NewInstance(1, argv));
}

equivalent.js

// I'm trying to approximate this;
Context.prototype.createEvent = function () {
  return new Event(this)
}

event.cc

NAN_METHOD(Event::New) {
  NanScope();

  if (!args.IsConstructCall()) {
    return NanThrowError("Event() must be called as a constructor");
  }

  Event* event;
  if (args.Length() == 1) {
    void* ptr = NanGetInternalFieldPointer(args[0].As<Object>(), 1);
    metadata_t* context = static_cast<metadata_t*>(ptr);
    // ptr is a nullptr here....
    event = new Event(context, false);
  } else {
    event = new Event();
  }

  event->Wrap(args.This());
  NanSetInternalFieldPointer(args.This(), 1, &event->event);
  NanReturnValue(args.This());
}

void Event::Init(Handle<Object> exports) {
  NanScope();

  // Prepare constructor template
  Handle<FunctionTemplate> ctor = NanNew<FunctionTemplate>(New);
  ctor->InstanceTemplate()->SetInternalFieldCount(2);
  ctor->SetClassName(NanNew<String>("Event"));
  NanAssignPersistent(constructor, ctor->GetFunction());

  exports->Set(NanNew<String>("Event"), ctor->GetFunction());
}