instanceof.cc

bool napi_instanceof(napi_env e, napi_value o, napi_value c) {
  v8::Isolate *isolate = v8impl::V8IsolateFromJsEnv(e);
  v8::Local<v8::Value> obj = v8impl::V8LocalValueFromJsValue(o);
  v8::Local<v8::Value> consProto = v8impl::V8LocalValueFromJsValue(c)
    ->ToObject()->Get(v8::String::NewFromUtf8(isolate, "prototype"));
  v8::Local<v8::String> protoString =
    v8::String::NewFromUtf8(isolate, "__proto__");

  while (!obj->IsNull()) {
    if (obj->StrictEquals(consProto)) {
      return true;
    }
    obj = obj->ToObject()->Get(protoString);
  }

return false;
}