I 'm wondering if i can add my own nodejs application server to this loraServer
Yes you can, when your nodejs application-server implements the application-server gRPC API interface: https://github.com/brocaar/loraserver/blob/master/api/as/as.proto
Or do you mean you want to integrate your nodejs application with LoRa App Server?
yes i want to integrate my own nodejs, backend application which supports mqtt, with only your lorawan network server.
In addition, I am using a private single channel lora gateway with rfm95w.