is there a way to use socket.io in a local area network without connection to the internet

Question

I built a flask chat app that uses socket.io to handle user to user communication. My problem is that the app is supposed to be working only in a LAN and when I am not connected to the internet, the app won't work.

Is there a way to preinstall scripts or to use another technology and to rewrite the code for the app to work?

Thanks for your answers.