<script>
window.addEventListener('load', async () => {
  const offerer = new RTCPeerConnection();
  const answerer = new RTCPeerConnection();
  offerer.addTransceiver('audio');
  await offerer.setLocalDescription();
  await answerer.setRemoteDescription(offerer.localDescription);
  const answer = await answerer.createAnswer();
  await offerer.setRemoteDescription(answer);
  // relay candidate with TCP!
  const candidate = 'candidate:3 1 tcp 18087935 20.253.151.225 3478 typ relay raddr 10.0.48.153 rport 3478 tcptype passive';
  await offerer.addIceCandidate({candidate, sdpMLineIndex: 0});
  await new Promise(r => setTimeout(r, 2000));
  self.close();
})
</script>
