How could others, on a local network, access my NodeJS app while it's running on my machine?

I have a pretty straight-forward question. I made a web game with NodeJS, and I can successfully play it by myself with multiple browser windows open side-by-side; however, I'd like to know if it's possible for other local machines to be able to access and play the game with me too.

I naively tried using this url: my-ip-address:8000 and it won't work.

Your node.js server is running on a port determined at the end of the script usually. Sometimes 3000. but can be anything. The correct way for others to access is as you say...

http://your.network.ip.address:port/

e.g.

http://192.168.0.3:3000

Check you have the correct port - and the IP address on the network - not the internet IP.

Otherwise, maybe the ports are being blocked by your router. Try using 8080 or 80 to get around this - otherwise re-configure your router.