Errors when ICE Candidates are received before answer is sent

The solution from Episodex helped me.

First setRemoteDescription, then create own stream, then create and send the answer.

  // On read message
  if (msg.sdp.type === 'offer') {

        this.peerConnection.setRemoteDescription(new RTCSessionDescription(msg.sdp))
          .then(() => navigator.mediaDevices.getUserMedia({audio: true, video: true}))
          .then(stream => this.peerConnection.addStream(stream));
          .then(() => this.peerConnection.createAnswer())
          .then(answer => this.peerConnection.setLocalDescription(answer))
          .then(() => this.sendMessage({sdp: this.peerConnection.localDescription}))

  } 

After I wrote this question an answer came into my mind... There is no need for attaching local stream before receiving ICE candidates, but remoteDescription should be set (which should be done at the moment of receiving offer). In my code I waited with setting remoteDescription and sending answer until browser gets the local stream.