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_step5_server.js

const socket = new binaryServer({
  port: 3001,
});

function playTone(tone, stream) {
  if (tone > 61 || tone < 1) {
    console.log('undefined tone', tone);
    return;
  }
  const filePath = path.resolve(__dirname, 'wav', `${tone}.wav`);
  const file = fs.createReadStream(filePath);
  file.pipe(stream);
  file.on('end', () => {
    file.unpipe(stream);
  });

  return file;
}
socket.on('connection', (client) => {
  client.on('stream', (stream, meta) => {

    stream.on('data', (data) => {
      console.log(data);
      const tone = data.readInt8(1);
      playTone(tone, stream);
    });

    stream.on('end', () => {
      console.log('end of stream');
    });
  });
});