So iroh is basically WebRTC, except it works in and outside of a browser. Relays seems quite similar to TURN/STUN servers except they also handle fallback traffic much like TOR guard/relay nodes
For browser / webapps you want webrtc.
[1]: PeerJS(https://peerjs.com/) is a library to use WebRTC w/o any boilerplate code. [2]: WebRTC functionality can be enabled in non-browser envs like Node.js by using third-party native addons (like node-webrtc) that provide bindings to the underlying C++ WebRTC library.