Notifications

Subscriptions deliver normalized DataView values and always return an unsubscribe function.

const characteristic = await service.getCharacteristic("2a19");
 
const unsubscribe = await characteristic.subscribe((value) => {
  console.log("battery:", value.getUint8(0));
});
 
// later
unsubscribe();

Why it works this way

Different runtimes deliver notifications through different event systems. The adapter normalizes them into one callback with one binary type, so application code written against the mock adapter behaves identically against hardware.

Lifecycle

Listen for the drop and reflect it:

device.on("disconnect", () => {
  // subscriptions are gone; update state, offer reconnect
});

Common failure

subscribe rejects with SUBSCRIPTION_FAILED when the characteristic does not support notifications. Check the device's characteristic properties — not every readable characteristic notifies.

Cleanup

Calling the returned unsubscribe function removes the listener and stops notifications best-effort. It is safe to call after a disconnect.

Next step

Error handling.