I understand adding the env to New() but not removing napi_enumerable as the signature seems like it requires that:

According to InstanceWrap doc:

template <typename T>
static Napi::ClassPropertyDescriptor<T>
Napi::InstanceWrap<T>::InstanceValue(const char* utf8name,
                            Napi::Value value,
                            napi_property_attributes attributes = napi_default);

napi_enumerable can be set but it is not required. I have verified that this code works.

But if you think that napi_enumerable needs to be included into this example then it still needs to be fixed because of wrong position of brackets:

InstanceValue("subObject", DefineProperties(Napi::Object::New(env), {
    InstanceMethod("decrement", &ExampleAddon::Decrement) // <- missing bracket
})/*) <- wrong bracket */, napi_enumerable)

Without napi_enumerable the items cannot be seen from JS without some effort. Please leave it in place! Everything else LGTM.

@gabrielschulhof I thought napi_enumerable means this items can be seen through for..in iteration or Object.keys as stated in the MDN's Enumerability and ownership of properties article. I thought without napi_enumerable the property still can be accessed through dot (obj.property) or brackets (obj['property']) or destructuring assignment ({ property } = obj) and there is no harm to remove napi_enumerable because there is no for..in iteration in addon.md.

So, I was wrong. I put napi_enumerable back in place. Does it mean that napi_enumerable needs to be added to other items too?

DefineAddon(exports, {
  InstanceMethod("increment", &ExampleAddon::Increment, napi_enumerable), // <- here

  // We can also attach plain objects to `exports`, and instance methods as
  // properties of those sub-objects.
  InstanceValue("subObject", DefineProperties(Napi::Object::New(env), {
    InstanceMethod("decrement", &ExampleAddon::Decrement, napi_enumerable) // <- and here
  }), napi_enumerable)
});