问信号的RTCDataChannel？

EN

var dc = null, sc = null, pc = new mozRTCPeerConnection(), live = false;
pc.onaddstream = e => v2.mozSrcObject = e.stream;
pc.ondatachannel = e => dc? scInit(sc = e.channel) : dcInit(dc = e.channel);
v2.onloadedmetadata = e => { log("Face time!"); };

function addTrack() {
  navigator.mediaDevices.getUserMedia({video:true, audio:true})
  .then(stream => pc.addStream(v1.mozSrcObject = stream));
}

pc.onnegotiationneeded = e => {
  pc.createOffer().then(d => pc.setLocalDescription(d)).then(() => {
    if (live) sc.send(JSON.stringify({ "sdp": pc.localDescription }));
  }).catch(failed);
};

function scInit() {
  sc.onmessage = e => {
    var msg = JSON.parse(e.data);
    if (msg.sdp) {
      var desc = new mozRTCSessionDescription(JSON.parse(e.data).sdp);
      if (desc.type == "offer") {
        pc.setRemoteDescription(desc).then(() => pc.createAnswer())
        .then(answer => pc.setLocalDescription(answer)).then(() => {
          sc.send(JSON.stringify({ "sdp": pc.localDescription }));
        }).catch(failed);
      } else {
        pc.setRemoteDescription(desc).catch(failed);
      }
    } else if (msg.candidate) {
      pc.addIceCandidate(new mozRTCIceCandidate(msg.candidate)).catch(failed);
    }
  };
}

function dcInit() {
  dc.onopen = () => { live = true; log("Chat!"); };
  dc.onmessage = e => log(e.data);
}

function createOffer() {
  button.disabled = true;
  dcInit(dc = pc.createDataChannel("chat"));
  scInit(sc = pc.createDataChannel("signaling"));
  pc.createOffer().then(d => pc.setLocalDescription(d)).catch(failed);
  pc.onicecandidate = e => {
    if (e.candidate) return;
    if (!live) {
      offer.value = pc.localDescription.sdp;
      offer.select();
      answer.placeholder = "Paste answer here";
    } else {
      sc.send(JSON.stringify({ "candidate": e.candidate }));
    }
  };
};

offer.onkeypress = e => {
  if (e.keyCode != 13 || pc.signalingState != "stable") return;
  button.disabled = offer.disabled = true;
  var obj = { type:"offer", sdp:offer.value };
  pc.setRemoteDescription(new mozRTCSessionDescription(obj))
  .then(() => pc.createAnswer()).then(d => pc.setLocalDescription(d))
  .catch(failed);
  pc.onicecandidate = e => {
    if (e.candidate) return;
    if (!live) {
      answer.focus();
      answer.value = pc.localDescription.sdp;
      answer.select();
    } else {
      sc.send(JSON.stringify({ "candidate": e.candidate }));
    }
  };
};

answer.onkeypress = e => {
  if (e.keyCode != 13 || pc.signalingState != "have-local-offer") return;
  answer.disabled = true;
  var obj = { type:"answer", sdp:answer.value };
  pc.setRemoteDescription(new mozRTCSessionDescription(obj)).catch(failed);
};

chat.onkeypress = e => {
  if (e.keyCode != 13) return;
  dc.send(chat.value);
  log(chat.value);
  chat.value = "";
};

var log = msg => div.innerHTML += "<p>" + msg + "</p>";
var failed = e => log(e.name + ": " + e.message + " line " + e.lineNumber);

<video id="v1" height="120" width="160" autoplay muted></video>
<video id="v2" height="120" width="160" autoplay></video><br>
<button id="button" onclick="createOffer()">Offer:</button>
<textarea id="offer" placeholder="Paste offer here"></textarea><br>
Answer: <textarea id="answer"></textarea><br>
<button id="button" onclick="addTrack()">AddTrack</button>
<div id="div"></div><br>
Chat: <input id="chat"></input><br>