A type-safe implementation of EventEmitter for browser and Node.js.
Despite event emitters potentially accepting any runtime value, defining a strict event contract is crucial when developing complex event-driven architectures. Unfortunately, the native type definitions for Node's EventEmitter annotate event names as string, which forbids any stricter type validation.
// index.js const emitter = new EventEmitter() // Let's say our application expects a "ping" // event with the number payload. emitter.on('ping', (n: number) => {}) // We can, however, emit a different event by mistake. emitter.emit('pong', 1) // Or even the correct event with the wrong data. emitter.emit('ping', 'wait, not a number')
The purpose of this library is to provide an EventEmitter instance that can accept a generic describing the expected events contract.
import { Emitter } from 'strict-event-emitter' // Define a strict events contract where keys // represent event names and values represent // the list of arguments expected in ".emit()". type Events = { ping: [number] } const emitter = new Emitter<Events>() emitter.addListener('ping', (n) => { // "n" argument type is inferred as "number'. }) emitter.emit('ping', 10) // OK emitter.emit('unknown', 10) // TypeError (invalid event name) emitter.emit('ping', 'wait, not a number') // TypeError (invalid data)
This library is also a custom EventEmitter implementation, which makes it compatible with other environments, like browsers or React Native.
npm install strict-event-emitter
import { Emitter } from 'strict-event-emitter' // 1. Define a type that describes your events. // Set event names as the keys, and their expected payloads as values. type Events = { connect: [id: string] disconnect: [id: string] } // 2. Create a strict emitter and pass the previously defined "Events" // as its first generic argument. const emitter = new Emitter<Events>() // 3. Use the "emitter" the same way you'd use the regular "EventEmitter" instance. emitter.addListener('connect', (id) => {}) emitter.emit('connect', 'abc-123')
MIT