PubSub (publish/subscribe)

Pubsub is a class implementing publisher/subscriber design pattern where messages are sent as promises

subscribe - event subscription

pubsub.subscribe('type', callback) - subscribe to event with name type. callback accepts as arguments payload from pubsub.publish. callback can return promise which will can be awaited from call pubsub.publish.
pubsub.subscribe returns the function to unsubscribe callback from the event.

publish - event publish

pubsub.publish('type', ...args) - publish event with name type. args will be passed as arguments to the subscribers. Return promise which will be resolved after resolve of all subscriptions.

Typed PubSub

PubSub can use typed events. For example: a common PubSub with many events and subscriptions.

In order to enable type checking for event subscriptions:

1. Create a new type with all event definitions:

type MyAwesomeFeatureEvents = {
  event1: (payload: number) => any;
  event2: (payload: { prop: boolean }) => any;
};

2. Do a typecast in code when using PubSub instance. It will enable type checks for every usage for a new typed instance

const featurePubSub = (pubSub as any) as PubSub<MyAwesomeFeatureEvents>;

// OK! 👍
featurePubSub.subscribe('event1', (payload) => console.log(1 + payload));
featurePubSub.publish('event1', 2);

// Error 👎
featurePubSub.subscribe('event3', (payload) => console.log(1 + payload)); // No such event
featurePubSub.publish('event3', 2); // НNo such event

featurePubSub.subscribe('event1', (payload) => payload.toLowerCase()); // Wrong payload type
featurePubSub.publish('event1', 'string'); // number expected