code/js-triad.html

<html>
<script>
  var audioCtx = new (window.AudioContext || window.webkitAudioContext)();

  var sample_rate = audioCtx.sampleRate; // 44100 hz
  var samples_per_frame = 1024;
  var inputChannelCount = 1; var outputChannelCount = 1;

  var scriptNode = audioCtx.createScriptProcessor(
    samples_per_frame, inputChannelCount, outputChannelCount
  );
  scriptNode.connect(audioCtx.destination);

  scriptNode.onaudioprocess = function (event) {
    var channelData = event.outputBuffer.getChannelData(0);

    for(var i = 0; i < samples_per_frame; i++) {
      var t = event.playbackTime + (i / sample_rate);

      channelData[i] =
          Math.sin(t * 2 * Math.PI * 440)
        + Math.sin(t * 2 * Math.PI * 556.875) / 2
        + Math.sin(t * 2 * Math.PI * 660) / 2;
    }
  }
</script>
<body>
</body>
</html>