Type safe event emitter

event_emitter.ts

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

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

    constructor() {}

    on<K extends keyof EventMap>(
        eventName: K,
        listener: Listener<EventMap[K]>,
    ) {
        //super.on(eventName as string, listener as (...args: any) => void);
        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 = {
    name: string;
    age: number;
};

type sUser = {
    dob: Date;
    city: string;
} & User;

type EventMap = {
    login: [user: User];
    signup: [user: sUser];
    logout: [];
};

const emitter = new MyEmitter<EventMap>();

emitter.on('login', (user) => {
    console.log(user);
});

emitter.on('signup', (user) => {
    console.log('signup ', user);
});

emitter.emit('login', {
    age: 10,
    name: 'John',
});

emitter.emit('signup', {
    age: 10,
    city: 'New York',
    dob: new Date(),
    name: 'John',
});

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