MediaStreamTrackAudioSourceOptions.mediaStreamTrack

mediaStreamTrackAudioSourceOptions = {
  mediaStreamTrack: audioSourceTrack;
}

mediaStreamTrackAudioSourceOptions.mediaStreamTrack = audioSourceTrack;

let audioCtx = new (window.AudioContext || window.webkitAudioContext)();

if (navigator.mediaDevices.getUserMedia) {
  navigator.mediaDevices.getUserMedia (
    {
      audio: true,
      video: false
    }).then(function(stream) {
      let options = {
        mediaStreamTrack: stream.getAudioTracks()[0];
      }

      let source = new MediaStreamTrackAudioSourceNode(audioCtx, options);
      source.connect(audioCtx.destination);
    }).catch(function(err) {
      console.log('The following gUM error occurred: ' + err);
    });
} else {
  console.log('new getUserMedia not supported on your browser!');
}