How is BackHandler is working in react Native

I was seeing the code of backhandler in react native. I understand that they are pushing the handler in _backPressSubscriptions. But after if condition they are removing it using removeEventListener in the return.

  addEventListener: function (
    eventName: BackPressEventName,
    handler: () => ?boolean,
  ): {remove: () => void, ...} {
    if (_backPressSubscriptions.indexOf(handler) === -1) {
      _backPressSubscriptions.push(handler);
    }
    return {
      remove: (): void => BackHandler.removeEventListener(eventName, handler),
    };
  },

Full code: https://github.com/facebook/react-native/blob/main/Libraries/Utilities/BackHandler.android.js

Also will BackHandler work on emulator?