event-emitter.ts

// by Simon Sturmer
// TypeScript: Building a better EventEmitter
// https://www.youtube.com/watch?v=Pl7pDjWd830
// Creative Commons-licence

type Listener<T extends Array<any>> = (...args: T) => void;

export class Eventemitter<EventMap extends Record<string, Array<any>>> {
    private eventListeners: {
        [K in keyof EventMap]?: Set<Listener<EventMap[K]>>;
    } = {};

    on<K extends keyof EventMap>(eventName: K, listener: Listener<EventMap[K]>) {
        const listeners = this.eventListeners[eventName] ?? new Set();
        listeners.add(listener);
        this.eventListeners[eventName] = listeners;
    }

    emit<K extends keyof EventMap>(eventName: K, ...args: EventMap[K]) {
        const listeners = this.eventListeners[eventName] ?? new Set();
        for (const listener of listeners) {
            listener(...args);
        }
    }
}

// ---

type User = {
    id: string;
    name: string;
}

type EventMap = {
    login: [user: User],
    logout: [],
}

const userAuthEmitter = new Eventemitter<EventMap>();

userAuthEmitter.on('login', (user) => {});

userAuthEmitter.emit('login', {id:'', name: ''});