`useCheckpointIdsListener`

The useCheckpointIdsListener hook registers a listener function with the Checkpoints object that will be called whenever its set of checkpoints changes.

useCheckpointIdsListener(
  listener: CheckpointIdsListener,
  listenerDeps?: DependencyList,
  checkpointsOrCheckpointsId?: any,
): void

	Type	Description
`listener`	`CheckpointIdsListener`	The function that will be called whenever the checkpoints change.
`listenerDeps?`	`DependencyList`	An optional array of dependencies for the `listener` function, which, if any change, result in the re-registration of the listener. This parameter defaults to an empty array.
`checkpointsOrCheckpointsId?`	`any`	The `Checkpoints` object to register the listener with: omit for the default context `Checkpoints` object, provide an `Id` for a named context `Checkpoints` object, or provide an explicit reference.
returns	`void`	This has no return value.

This hook is useful for situations where a component needs to register its own specific listener to do more than simply tracking the value (which is more easily done with the useCheckpointIds hook).

Unlike the addCheckpointIdsListener method, which returns a listener Id and requires you to remove it manually, the useCheckpointIdsListener hook manages this lifecycle for you: when the listener changes (per its listenerDeps dependencies) or the component unmounts, the listener on the underlying Checkpoints object will be deleted.

Example

This example uses the useCheckpointIdsListener hook to create a listener that is scoped to a single component. When the component is unmounted, the listener is removed from the Store.

const App = ({checkpoints}) => (
  <Provider checkpoints={checkpoints}>
    <Pane />
  </Provider>
);
const Pane = () => {
  useCheckpointIdsListener(() => console.log('Checkpoint Ids changed'));
  return <span>App</span>;
};

const store = createStore().setTables({pets: {fido: {sold: false}}});
const checkpoints = createCheckpoints(store);

const app = document.createElement('div');
const root = ReactDOMClient.createRoot(app);
root.render(<App checkpoints={checkpoints} />);
console.log(checkpoints.getListenerStats().checkpointIds);
// -> 1

store.setCell('pets', 'fido', 'sold', true);
// -> 'Checkpoint Ids changed'
checkpoints.addCheckpoint();
// -> 'Checkpoint Ids changed'

root.unmount();
console.log(checkpoints.getListenerStats().checkpointIds);
// -> 0