how to get the Napi::Function constructor of an object?

[sezanzeb]

I can't figure out how to get the Napi::Function& constructor of an object. I would like to use InstanceOf (https://github.com/nodejs/node-addon-api/blob/main/doc/object.md#instanceof)

It looks like a constructor is extracted from an object using Napi::Type::Type, like in https://github.com/nodejs/node-addon-api/blob/main/doc/function.md#constructor, but when I use Napi::Date::Date, I get the following problem:

error: cannot convert ‘<unresolved overloaded function type>’ to ‘const Napi::Function&’
   59 |       bool is_date = value.ToObject().InstanceOf(Napi::Date::Date);
      |                            

I don't know much about c++ by the way

[KevinEady]

There is no way to retrieve an object's constructor within Node API. You might be able to call Object.getPrototypeOf(), maybe like (untested):

auto objGlobal = env.Global().Get("Object");
auto getPrototypeOf = objGlobal.As<Object>().Get("getPrototypeOf").As<Function>();
auto prototype = getPrototypeOf.Call(objGlobal, { value }); // where `value` is the object whose prototype you want to receive

[sezanzeb]

thanks, but I think I'm not trying to get an objects constructor, but rather the constructor for a given type.

How would you recommend to check if an object is of type Date? I'll try value.ToObject().Has('getTime') tomorrow

[NickNaso]

Hi @sezanzeb,
to check if a value is a JavaScript object you could use the Napi::Value::IsDate method see: https://github.com/nodejs/node-addon-api/blob/main/doc/value.md#isdate
Es.

Napi::Value Method(const Napi::CallbackInfo& info) {
  bool isDate = info[0].IsDate();
  return Napi::Boolean::New(env, isDate);
}

I hope tha this help you.

[github-actions]

This issue is stale because it has been open many days with no activity. It will be closed soon unless the stale label is removed or a comment is made.

[mhdawson]

Closing since there as been no follow up since Nick's response. Please let us know if that was not the right thing to do.