midi-ble-peripheral.js

var midiService = {
    uuid: MIDI_SERVICE_UUID,
    characteristics: [
        {
            uuid: MIDI_CHARACTERISTIC_UUID,
            properties: property.WRITE | property.READ | property.NOTIFY,
            permissions: permission.WRITEABLE | permission.READABLE,
            descriptors: [
                {
                    uuid: '2901',
                    value: 'MIDI'
                }
            ]
        }
    ]
};

blePeripheral.createServiceFromJSON(midiService);

// https://github.com/don/cordova-plugin-ble-peripheral

send-note.js

var channel = 10;
var midiNote = 49; // crash cymbal
var velocity = 127;

var noteOn = new Uint8Array([0x80, 0x80, 0x90 + channel, midiNote, velocity]);

blePeripheral.setCharacteristicValue(
  MIDI_SERVICE_UUID, 
  MIDI_CHARACTERISTIC_UUID, 
  noteOn.buffer
).then(success, failure);