Tutorial. How to create MIDI synthesizer with MIDI API and Node JS https://medium.com/nebo-15/tutorial-how-to-create-midi-synthesizer-with-midi-api-and-node-js-48d41c162009

midi-api_step6_client.js

function playSound(audioBuffer) {
  var source = context.createBufferSource();
  source.buffer = audioBuffer;
  source.connect(context.destination);
  source.start(0);
  console.timeEnd('send');
}
function handleMidiMessage(e) {
  if (!MIDIStream || e.data[0] !== 0x90) return;
  console.log(e);
  console.time('send');
  MIDIStream.write(e.data);
}