Record internal audio of a website via javascript

<html>
<head>
<script>

const context = new(window.AudioContext || window.webkitAudioContext)()

async function run()
{
    var myArrayBuffer = context.createBuffer(2, context.sampleRate, context.sampleRate);
    // Fill the buffer with white noise;
    // just random values between -1.0 and 1.0
    for (var channel = 0; channel < myArrayBuffer.numberOfChannels; channel++) {
      // This gives us the actual array that contains the data
      var nowBuffering = myArrayBuffer.getChannelData(channel);
      for (var i = 0; i < myArrayBuffer.length; i++) {
        // audio needs to be in [-1.0; 1.0]
        nowBuffering[i] = Math.random() * 2 - 1;
      }
    }
    playAudio(myArrayBuffer)
}

function playAudio(buf){
    const streamNode = context.createMediaStreamDestination();
    const stream = streamNode.stream;
    const recorder = new MediaRecorder( stream );
    const chunks = [];
    recorder.ondataavailable = evt => chunks.push( evt.data );
    recorder.onstop = evt => exportAudio( new Blob( chunks ) );

    const source = context.createBufferSource()
    source.onended = () => recorder.stop();
    source.buffer = buf
    source.playbackRate.value = 0.2
    source.connect( streamNode );
    source.connect(context.destination);
    source.start(0)
    recorder.start();
}

function exportAudio( blob ) {
  const aud = new Audio( URL.createObjectURL( blob ) );
  aud.controls = true;
  document.body.prepend( aud );
}


</script>
</head>
<body onload="javascript:run()">
<input type="button" onclick="context.resume()" value="play"/>
</body>
</html>