withSubscribe

withSubscribe<T, E>(target: T & Partial<{ subscribe: SubscribeFunc<E>; }>): T & { subscribe: SubscribeFunc<E>; }

Defined in: extras/with-subscribe.ts:30

Enhances a StateMachine with a subscribe method for event notifications. Powered by emitter, this function allows external code to subscribe to events emitted by the state machine.

Use cases:

• Adding pub/sub capability to state machines
• Allowing external listeners to react to state changes or events
• Useful for event-driven architectures and reactive programming

Type Parameters

Type Parameter	Description
T extends Pick<StateMachine<any>, "notify">	The StateMachine type with a notify method
E extends any	The event type handled by notify

Parameters

Parameter	Type	Description
target	T & Partial<{ subscribe: SubscribeFunc<E>; }>	The state machine to enhance

Returns

T & { subscribe: SubscribeFunc<E>; }

The enhanced state machine with a subscribe method

Example

const machine = { notify: (ev: string) => undefined };
const enhanced = withSubscribe(machine);
enhanced.subscribe((ev: string) => console.log('Event:', ev));
enhanced.notify('test'); // Logs: 'Event: test'

Source

This function is useful for scenarios where you want to allow external code to subscribe to events or changes emitted by a state machine. It wraps the notify method to emit events to subscribers, enabling reactive patterns and decoupled event handling.

export const withSubscribe = <
  T extends Pick<StateMachine<any>, "notify">,
  E extends Parameters<T["notify"]>[0],
>(
  target: T & Partial<{ subscribe: SubscribeFunc<E> }>
) => {
  if (!target.subscribe) {
    const notify = target.notify.bind(target);
    const [subscribe, emit] = emitter<Parameters<T["notify"]>[0]>();
    target.notify = (ev) => {
      notify(ev);
      emit(ev);
    };
    target.subscribe = subscribe;
  }
  return target as T & { subscribe: typeof target.subscribe };
};

See

emitter for the underlying pub/sub implementation