Class MIDIPlayer

If you want to use a particular MIDI output port, you must update the output property before calling start, otherwise a message will be sent to all connected MIDI outputs:

Example (easy mode):

   const player = new mm.MIDIPlayer();
   player.requestMIDIAccess().then(() => {
     // For example, use only the first port. If you omit this,
     // a message will be sent to all ports.
     player.outputs = [player.availableOutputs[0]];
     player.start(seq);
   })

If you want to specify which MIDI channel the messages should be sent on, you can set the outputChannel property before calling start. By default, the outputChannel is 0.

You can also explicitly request MIDI access outside of the player, in your application, and just update the output property before playing:

Example (advanced mode):

   navigator.requestMIDIAccess().then((midi) => {
      // Get all the MIDI outputs to show them in a <select> (for example)
      const availableOutputs = [];
      const it = midi.outputs.values();
      for (let o = it.next(); o && !o.done; o = it.next()) {
         availableOutputs.push(o.value);
      }
      // Populate the <select>
      const el = document.querySelector('select');
      el.innerHTML = availableOutputs.map(i =>
          `<option>${i.name}</option>`).join('');

      // Use the selected output port.
      player = new mm.MIDIPlayer();
      player.outputs = [availableOutputs[el.selectedIndex]];
      player.start(seq)
    });