Javascript WebRTC Failed to set remote answer sdp: Called in wrong state: kHaveRemoteOffer and Called in wrong state: kStable

My website where I use it: https://www.camspark.com/
Fixed myself I figured out I had 2 problems with this code.

First problem was then createOffer() must only be sent by 1 person not both people.. you have to randomly pick which person which does the createOffer().

Second problem is the ICE Candidate's you have to create a queue/array for both sides, which holds all the incoming ice_candidates. Only do the peerConnection.addIceCandidate(new IceCandidate(candidate)); when the response to createOffer() is received and the setRemoteDescription from createOffer() response is set up.

Both getAnswer() and getOffer() use exactly same code, but one is received for 1 client while the other is received for the other client. Both need to flush the IceCandidates array when either of them is triggered.. Maybe if anyone wants you could combine both functions into 1 function as the code is the same.

Final working code looks like this

var ws;

var peerConnection, localStream;  
//STUN = (Session Traversal Utilities for NAT)  
var rtc_server = {
  iceServers: [
                {urls: "stun:stun.l.google.com:19302"},
                {urls: "stun:stun.services.mozilla.com"},
                {urls: "stun:stun.stunprotocol.org:3478"},
                {url: "stun:stun.l.google.com:19302"},
                {url: "stun:stun.services.mozilla.com"},
                {url: "stun:stun.stunprotocol.org:3478"},
  ]
}

//offer SDP = [Session Description Protocol] tells other peers what you would like
var rtc_media_constraints = {
  mandatory: {
    OfferToReceiveAudio: true,
    OfferToReceiveVideo: true
  }
};

var rtc_peer_options = {
  optional: [
              {DtlsSrtpKeyAgreement: true}, //To make Chrome and Firefox to interoperate.
  ]
}
var finishSDPVideoOffer = false;
var isOfferer = false;
var iceCandidates = [];
var PeerConnection = RTCPeerConnection || window.PeerConnection || window.webkitPeerConnection || window.webkitRTCPeerConnection || window.mozRTCPeerConnection;
var IceCandidate = RTCIceCandidate || window.mozRTCIceCandidate || window.RTCIceCandidate;
var SessionDescription = RTCSessionDescription || window.mozRTCSessionDescription || window.RTCSessionDescription;
var getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;

function hasSupportForVideoChat() {
   return window.RTCPeerConnection && window.RTCIceCandidate && window.RTCSessionDescription && navigator.mediaDevices && navigator.mediaDevices.getUserMedia && (RTCPeerConnection.prototype.addStream || RTCPeerConnection.prototype.addTrack) ? true : false;
}

function loadMyCameraStream() {
    if (getUserMedia) {
      getUserMedia.call(navigator, { video: {facingMode: "user", aspectRatio: 4 / 3/*height: 272, width: 322*/}, audio: { echoCancellation : true } },
        function(localMediaStream) {
          //Add my video
          $("div#videoBox video#you")[0].muted = true;
          $("div#videoBox video#you")[0].autoplay = true;
          $("div#videoBox video#you").attr('playsinline', '');
          $("div#videoBox video#you").attr('webkit-playsinline', '');
          $("div#videoBox video#you")[0].srcObject = localMediaStream;
          localStream = localMediaStream;
        },
        function(e) {
          addStatusMsg("Your Video has error : " + e);
        }
      );
    } else {
      addStatusMsg("Your browser does not support WebRTC (Camera/Voice chat).");
      return;
    }
}

function loadStrangerCameraStream(isOfferer_) {
    if(!hasSupportForVideoChat())
      return;

    //Only add pending ICE Candidates when getOffer() is finished.
    finishSDPVideoOfferOrAnswer = false;
    iceCandidates = []; //clear ICE Candidates array.
    isOfferer = isOfferer_;

    peerConnection = new PeerConnection(rtc_server, rtc_peer_options);
    if (peerConnection.addTrack !== undefined)
      localStream.getTracks().forEach(track => peerConnection.addTrack(track, localStream));
    else
      peerConnection.addStream(localStream);

    peerConnection.onicecandidate = function(e) {
      if (!e || !e.candidate)
        return;    
      ws.send(JSON.stringify(['ice_candidate', {"candidate": e.candidate}]));
    };

    if (peerConnection.addTrack !== undefined) {
      //newer technology
      peerConnection.ontrack = function(e) {
        //e.streams.forEach(stream => doAddStream(stream));
        addStatusMsg("ontrack called");
        //Add stranger video
        $("div#videoBox video#stranger").attr('playsinline', '');
        $("div#videoBox video#stranger").attr('webkit-playsinline', '');
        $('div#videoBox video#stranger')[0].srcObject = e.streams[0];
        $("div#videoBox video#stranger")[0].autoplay = true;
      };
    } else {
      //older technology
      peerConnection.onaddstream = function(e) {
        addStatusMsg("onaddstream called");
        //Add stranger video
        $("div#videoBox video#stranger").attr('playsinline', '');
        $("div#videoBox video#stranger").attr('webkit-playsinline', '');
        $('div#videoBox video#stranger')[0].srcObject = e.stream;
        $("div#videoBox video#stranger")[0].autoplay = true;
      };
    }

    if(isOfferer) {
      peerConnection.createOffer(
        function(offer) {
          peerConnection.setLocalDescription(offer, function () {
            //both offer and peerConnection.localDescription are the same.
            addStatusMsg('createOffer, localDescription: ' + JSON.stringify(peerConnection.localDescription));
            //addStatusMsg('createOffer, offer: ' + JSON.stringify(offer));
            ws.send(JSON.stringify(['send_offer', {"offer": peerConnection.localDescription}]));
          },
          function(e) {
            addStatusMsg('createOffer, set description error' + e);
          });
        },
        function(e) {
          addStatusMsg("createOffer error: " + e);
        },
        rtc_media_constraints
      );
    }
}

function closeStrangerCameraStream() {
    $('div#videoBox video#stranger')[0].srcObject = null
    if(peerConnection)
      peerConnection.close();
}     

function iceCandidate(candidate) {
  //ICE = Interactive Connectivity Establishment
  if(!finishSDPVideoOfferOrAnswer) {
    iceCandidates.push(candidate);
    addStatusMsg("Queued iceCandidate");
    return;
  }

  if(!peerConnection) {
    addStatusMsg("iceCandidate peerConnection not created error.");
    return;
  }

  peerConnection.addIceCandidate(new IceCandidate(candidate));
  addStatusMsg("Added on time, Peer Ice Candidate = " + JSON.stringify(candidate));
}

function getAnswer(answer) {    
    if(!hasSupportForVideoChat())
      return;

    if(!peerConnection) {
      addStatusMsg("getAnswer peerConnection not created error.");
      return;
    }

    peerConnection.setRemoteDescription(new SessionDescription(answer), function() {
      addStatusMsg("getAnswer SessionDescription answer is ok");
      finishSDPVideoOfferOrAnswer = true;
      while (iceCandidates.length) {
        var candidate = iceCandidates.shift();
        try {
          peerConnection.addIceCandidate(new IceCandidate(candidate));
          addStatusMsg("Adding queued ICE Candidates");
        } catch(e) {
          addStatusMsg("Error adding queued ICE Candidates error:" + e);
        }
      }
      iceCandidates = [];
    },
    function(e) {
      addStatusMsg("getAnswer SessionDescription fail error: " + e);
    });
}

function getOffer(offer) {
    if(!hasSupportForVideoChat())
      return;

    if(!peerConnection) {
      addStatusMsg("getOffer peerConnection not created error.");
      return;
    }

    addStatusMsg("getOffer setRemoteDescription offer: " + JSON.stringify(offer));
    peerConnection.setRemoteDescription(new SessionDescription(offer), function() {
      finishSDPVideoOfferOrAnswer = true;
      while (iceCandidates.length) {
        var candidate = iceCandidates.shift();
        try {
          peerConnection.addIceCandidate(new IceCandidate(candidate));
          addStatusMsg("Adding queued ICE Candidates");
        } catch(e) {
          addStatusMsg("Error adding queued ICE Candidates error:" + e);
        }
      }
      iceCandidates = [];
      if(!isOfferer) {
        peerConnection.createAnswer(
          function(answer) {
            peerConnection.setLocalDescription(answer);
            addStatusMsg("getOffer create answer sent: " + JSON.stringify(answer));
            ws.send(JSON.stringify(['send_answer', {"answer": answer}]));
          },
          function(e) {
            addStatusMsg("getOffer setRemoteDescription create answer fail: " + e);
          }
        );
      }
    });
}

Here is the patch I did on server-side WebSocket (Java) server.

//JSON
 //["connected", {videoChatOfferer: true}]
 //["connected", {videoChatOfferer: false}]
 JSONObject obj = new JSONObject();
 JSONArray list = new JSONArray();
 list.put("loadStrangerCameraStream");
 obj.put("videoChatOfferer", true); //first guy offerer for WebRTC.
 list.put(obj);
 server.sendMessage(websocket, list.toString()); //connected to chat partner
 obj.put("videoChatOfferer", false); //second guy isn't offerer.
 list.put(obj);
 server.sendMessage(stranger.getWebSocket(), list.toString()); //connected to chat partner