bindMidiHandler.js

// Binds events from the first midi device
function bindMidiHandler(myMIDIMessagehandler){
  var m = null; // m = MIDIAccess object for you to make calls on

  function onsuccesscallback( access ) {
    m = access;

    // Things you can do with the MIDIAccess object:
    var inputs = m.inputs; // inputs = MIDIInputMaps, you can retrieve the inputs with iterators
    var outputs = m.outputs; // outputs = MIDIOutputMaps, you can retrieve the outputs with iterators

    var iteratorInputs = inputs.values() // returns an iterator that loops over all inputs
    var input = iteratorInputs.next().value // get the first input

    if (input) {
      input.onmidimessage = myMIDIMessagehandler;
    }
  };

  function onerrorcallback( err ) {
    console.log( "uh-oh! Something went wrong! Error code: " + err.code );
  }

  navigator.requestMIDIAccess().then( onsuccesscallback, onerrorcallback );
}