How to make a web app for your own Bluetooth Low Energy device? Step 12

main.js

// Enable the characteristic changes notification
function startNotifications(characteristic) {
  log('Starting notifications...');

  return characteristic.startNotifications().
      then(() => {
        log('Notifications started');
        // Added line
        characteristic.addEventListener('characteristicvaluechanged',
            handleCharacteristicValueChanged);
      });
}

function disconnect() {
  if (deviceCache) {
    log('Disconnecting from "' + deviceCache.name + '" bluetooth device...');
    deviceCache.removeEventListener('gattserverdisconnected',
        handleDisconnection);

    if (deviceCache.gatt.connected) {
      deviceCache.gatt.disconnect();
      log('"' + deviceCache.name + '" bluetooth device disconnected');
    }
    else {
      log('"' + deviceCache.name +
          '" bluetooth device is already disconnected');
    }
  }

  // Added condition
  if (characteristicCache) {
    characteristicCache.removeEventListener('characteristicvaluechanged',
        handleCharacteristicValueChanged);
    characteristicCache = null;
  }

  deviceCache = null;
}

// Data receiving
function handleCharacteristicValueChanged(event) {
  let value = new TextDecoder().decode(event.target.value);
  log(value, 'in');
}