C Header file

Class Header file

class PiWorker : public Napi::AsyncWorker {
public:
  PiWorker(Napi::Env &env, int points)
      : Napi::AsyncWorker(env), points(points), estimate(0),
        deferred(Napi::Promise::Deferred::New(env)) {}
  ~PiWorker() {}
  void Execute();
  void OnOK();
  void OnError(Napi::Error const &error);
  Napi::Promise GetPromise();

private:
  int points;
  double estimate;
  Napi::Promise::Deferred deferred;
};

void PiWorker::OnOK() {
  Object obj = Napi::Object::New(Env());
  obj.Set("estimate", Number::New(Env(), estimate));
  deferred.Resolve(obj);
}
void PiWorker::Execute() { estimate = 4.0; }
void PiWorker::OnError(Error const &error) { deferred.Reject(error.Value()); }
Promise PiWorker::GetPromise() { return deferred.Promise(); }

Separating class code into a header and cpp file

Asked I am confused on how to separate implementation and declarations code of a simple class into a new header and cpp file. For example, how would I separate the code for the following class?

https://stackoverflow.com/questions/9579930/separating-class-code-into-a-header-and-cpp-file