Simple TypeScript EventBus

event-bus.ts

export type Event<T> = {
    event: T;
};

export type BaseEvent = Event<string>;

export type GenericCallback<T extends BaseEvent> = (data: Extract<T, { event: T['event'] }>) => void;
export type Callback<T extends BaseEvent, K extends T['event']> = (data: Extract<T, { event: K }>) => void;

export class EventBus<T extends BaseEvent> {
    private channel: BroadcastChannel;
    private listeners: Map<T['event'], [unknown, GenericCallback<T>][]>;

    constructor(name: string) {
        this.channel = new BroadcastChannel(name);
        this.listeners = new Map();
    }

    emit<K extends T['event']>(event: K, data: Omit<Extract<T, { event: K }>, 'event'>) {
        this.channel.postMessage({ event, data });
    }

    subscribe<K extends T['event']>(owner: unknown, event: K, callback: Callback<T, K>) {
        if (!this.listeners.has(event)) {
            this.listeners.set(event, []);
        }
        this.listeners.get(event)?.push([owner, callback as unknown as GenericCallback<T>]);
    }

    unsubscribe(owner: unknown) {
        for (const [event, listeners] of this.listeners) {
            this.listeners.set(event, listeners.filter(([listenerOwner]) => listenerOwner !== owner));
        }
    }
}