WebRTC sample hello world

p2p.ts

interface Signaller {
  send(data: unknown): void;
  onmessage(data: unknown): void;
}

const ls = {
  send: (x) => rs.onmessage(x),
} as Signaller;
const rs = {
  send: (x) => ls.onmessage(x),
} as Signaller;

const local = createPc(ls);

const remote = createPc(rs);
remote.ondatachannel = (dc) => {
  dc.channel.onmessage = (e) => {
    console.log(dc.channel.label, e.data);
  };
};

const dc = local.createDataChannel('txt');
dc.onopen = () => {
  dc.send('hello');
};

function createPc(signaller: Signaller, cfg = null, polite = true) {
  const pc = new RTCPeerConnection(cfg);

  let makingOffer = false;
  pc.onnegotiationneeded = async () => {
    try {
      makingOffer = true;
      await pc.setLocalDescription(undefined);
      signaller.send({ description: pc.localDescription });
    } finally {
      makingOffer = false;
    }
  };

  pc.onicecandidate = ({ candidate }) => {
    if (candidate) {
      signaller.send({ candidate });
    }
  };

  signaller.onmessage = async ({
    description,
    candidate,
  }: {
    description: RTCSessionDescription;
    candidate: RTCIceCandidate;
  }) => {
    let ignoreOffer = false;
    if (description) {
      const isOffer = description.type == 'offer';
      const offerCollision =
        isOffer && (makingOffer || pc.signalingState != 'stable');

      ignoreOffer = !polite && offerCollision;
      if (ignoreOffer) {
        return;
      }

      await pc.setRemoteDescription(description);
      if (isOffer) {
        await pc.setLocalDescription(undefined);
        signaller.send({ description: pc.localDescription });
      }
    } else if (candidate) {
      try {
        await pc.addIceCandidate(candidate);
      } catch (err) {
        if (!ignoreOffer) {
          throw err;
        }
      }
    }
  };

  return pc;
}

https://developer.mozilla.org/en-US/docs/Web/API/WebRTC_API/Perfect_negotiation