pubsubby

Typed PubSub library for TypeScript (publish-subscribe). It is a lightweight and depedency-free package.

When is this useful?

Whenever you need to create a typed event emitter and have consumers (functions) subscribe to it. For instance:

1. Domain Events
2. Use cases in (Clean Architecture) expose typed events (e.g. UserRegistered, PostDeleted)
3. Event-based browser interactions

Concepts

Event – a type or interface that describes the contents of the event

EventEmitter (interface) – the publisher that stores consumers and emits Event

SimpleEventEmitter – a simple-yet-working implemention of the EventEmitter interface

Consumer – a function that subscribes to an EventEmitter and receives its published Event data

Subscription – a simple object containing the subscription's key and an unsubscribe method

The source code is very simple so take a look at the src/ folder.

Example

Check out the tests/ folder for quick examples but otherwise the below should work too.

type DateTimeChanged = {
    datetime: Date
}

// Instanciate the emitter (e.g. in your use case's class)
const emitter = new SimpleEventEmitter<DateTimeChanged>()

// Create your event consumer
const consumer = async (event: DateTimeChanged) => {
    // Handle the event the way you want:
    // 1. parse, convert and publish to Kafka, AWS SQS, or GCP PubSub
    // 2. persist this to disk, or database
    // 3. here we just log that to the console
    console.log(`new event received:`, event)
}

// Subscribe that consumer to the emitter
const subscription = await emitter.subscribe(consumer)

// Emit an event (typed as DateTimeChanged automatically)
await emitter.publish({
    datetime: new Date(),
})

// You should see the event in the console

// f you want, unsubscribe the from subscription
subscription.unsubscribe()
// or from the emitter with the subscription key
emitter.unsubscribe(subscription.key)