window.onload = function demo() {

  // create peer connection
  let pc = new RTCPeerConnection({
    iceCandidatePoolSize: 4
  });

  // create websocket for signaling channel
  let ws = new WebSocket('ws://localhost:8080');

  // (callback) called upon discovery of new local ICE candidate
  pc.onicecandidate = function(event) {
    if (event.candidate) {
      console.log("local candidate:\n%c%s", "color: green", event.candidate.candidate);
      ws.send(JSON.stringify(event.candidate));
    }
  };

  // (callback) called upon reception of new remote video track
  pc.ontrack = function(event) {
    document.getElementById("remoteVideo").srcObject = event.streams[0];
  };

  // receive remote answer or candidate
  ws.onmessage = function(event) {
    try {
      let d = JSON.parse(event.data);
      if ('candidate' in d) {
        if (d.candidate) {
          console.log("remote candidate:\n%c%s", "color: blue;", d.candidate);
					pc.addIceCandidate(d).catch((e) => {
						console.log("addIceCandidate:\n%c%s", "color: red;", e);
					});
        }
      } else if ('sdp' in d) {
				pc.setRemoteDescription(d).catch((e) => {
					console.log("setRemoteDescription:\n%c%s", "color: red;", e);
				});
        console.log("remote answer:\n%c%s", "color: blue;", d.sdp);
      }
    } catch(e) {
      console.log("remote error:\n%c%s", "color: red;", event.data);
    }
  };

  // create offer and set to remote peer
  ws.onopen = function(event) {
    pc.createOffer({ offerToReceiveVideo: true }).then(function(offer) {
      console.log("local offer:\n%c%s", "color: green;", offer.sdp);
      pc.setLocalDescription(offer);
      ws.send(JSON.stringify(offer));
    });
  };
}