channel - WebRTC DataChannel Errors -

i'm trying connect 2 peers webrtc , datachannel without camera , microphone.

try {             socket = new websocket("ws://localhost:1337/");             var servers = {iceservers:[{url:"stun:stun.l.google.com:19302"}]};             peerconn = new webkitrtcpeerconnection(servers, {optional:[{rtpdatachannels: true}]});             channel = peerconn.createdatachannel("abcd1234", {reliable: false});              peerconn.onicecandidate = function(evt) {                 if(evt.candidate) {                     socket.send(json.stringify({"candidate": evt.candidate}));                 }             };              channel.onopen = function () {                 console.log("channel open");                 channel.send('first text message on rtp data ports');             };              channel.onmessage = function (event) {                 console.log('received message:', event.data);             };              peerconn.createoffer(function(desc) {                 peerconn.setlocaldescription(desc);                 socket.send(json.stringify({"sdp": desc}));             });              socket.onmessage = function(evt) {                 var signal = json.parse(evt.data);                 if(signal.sdp) {                      peerconn.setremotedescription(new rtcsessiondescription(signal.sdp));                     alert("desc");                 } else {                      peerconn.addicecandidate(new rtcicecandidate(signal.candidate));                     alert("ice");                 }             }         } catch(e) {             console.log(e.message);         } 

in chrome errors out with:

uncaught error: invalidstateerror: dom exception 11 

open 2 tabs; click "create offer" button 1st tab; , watch console logs:

<script>     // webkitrtcpeerconnection && rtcdatachannel specific code goes here     var iceservers = {         iceservers: [{             url: 'stun:stun.l.google.com:19302'         }]     };      var optionalrtpdatachannels = {         optional: [{             rtpdatachannels: true         }]     };      var mediaconstraints = {         optional: [],         mandatory: {             offertoreceiveaudio: false, // hmm!!             offertoreceivevideo: false // hmm!!         }     };      var offerer, answerer, answererdatachannel, offererdatachannel;      function createoffer() {         offerer = new webkitrtcpeerconnection(iceservers, optionalrtpdatachannels);          offererdatachannel = offerer.createdatachannel('rtcdatachannel', {             reliable: false         });          setchannelevents(offererdatachannel, 'offerer');          offerer.onicecandidate = function (event) {             if (!event.candidate) returnsdp();         };          offerer.ongatheringchange = function (event) {             if (event.currenttarget && event.currenttarget.icegatheringstate === 'complete') returnsdp();         };          function returnsdp() {             socket.send({                 sender: 'offerer',                 sdp: offerer.localdescription             });         }          offerer.createoffer(function (sessiondescription) {             offerer.setlocaldescription(sessiondescription);         }, null, mediaconstraints);     }       function createanswer(offersdp) {         answerer = new webkitrtcpeerconnection(iceservers, optionalrtpdatachannels);         answererdatachannel = answerer.createdatachannel('rtcdatachannel', {             reliable: false         });          setchannelevents(answererdatachannel, 'answerer');          answerer.onicecandidate = function (event) {             if (!event.candidate) returnsdp();         };          answerer.ongatheringchange = function (event) {             if (event.currenttarget && event.currenttarget.icegatheringstate === 'complete') returnsdp();         };          function returnsdp() {             socket.send({                 sender: 'answerer',                 sdp: answerer.localdescription             });         }          answerer.setremotedescription(new rtcsessiondescription(offersdp));         answerer.createanswer(function (sessiondescription) {             answerer.setlocaldescription(sessiondescription);         }, null, mediaconstraints);     }      function setchannelevents(channel, channelnameforconsoleoutput) {         channel.onmessage = function (event) {             console.debug(channelnameforconsoleoutput, 'received message:', event.data);         };          channel.onopen = function () {             channel.send('first text message on rtp data ports');         };     }      // websocket specific code goes here     var socket = new websocket('ws://localhost:1337');     socket.onmessage = function (e) {         var data = json.parse(e.data);         console.log(data);         if (data.sdp) {             if (data.sender == 'offerer') createanswer(data.sdp);             else offerer.setremotedescription(new rtcsessiondescription(data.sdp));         }     };      socket.push = socket.send;     socket.send = function (data) {         socket.push(json.stringify(data));     }; </script>  <button id="create-offer">create offer</button> <script>     document.getelementbyid('create-offer').onclick = function () {         this.disabled = true;         createoffer();     }; </script>