Signal

Signals are dispatchable events.

import { signal } from 'amos';

const signOutSignal = signal<{ userId: number; keepData: boolean }>('user.signOut');

Subscribe to a signal:

signOutSignal.subscribe((dispatch, select, event) => {
  if (!event.keepData) {
    dispatch(currentUserIdBox.setState(0));
  }
});

Dispatch it like any other dispatchable:

dispatch(signOutSignal({ userId: 1, keepData: false }));

Why Signals Exist

Actions are good for workflows. Signals are good for events that many modules may care about.

For example, the user module can dispatch signOutSignal, while the todo module subscribes to clean todo state.

todoMapBox.subscribe(signOutSignal, (state, event) => {
  return event.keepData ? state : state.clear();
});

The user module does not need to import todo cleanup code.

The simplest signal uses its first argument as data.

const selected = signal<number>('item.selected');

dispatch(selected(1));

You can also provide a creator that derives signal data from current state.

const currentUserChanged = signal('user.currentChanged', (select) => {
  return select(currentUserIdBox);
});

dispatch(currentUserChanged());

Every box has subscribe(signal, fn).

currentUserIdBox.subscribe(signOutSignal, () => 0);

This helper subscribes to the signal and dispatches box.setState(nextState) for you.