Events (revised)

[Daniel Dietrich]

Candid claims to be unopinionated but ships with its own messaging solution (pub-sub). It is better to move pub-sub to its own library.

export type Topic = string;
export type Subscriptions = Set<Subscriber<any>>;
export type Subscriber<T> = (e: T) => void;
export type Unsubscribe = () => void;

export default {
    publish,
    subscribe
};

const topics: Map<Topic, Subscriptions> = new Map();

/**
 * Subscribes a subscriber to a certain topic.
 * Returns an unsubscribe function.
 */
function subscribe<T>(topic: Topic, subscriber: Subscriber<T>): Unsubscribe {
    let subscriptions = topics.get(topic);
    if (!subscriptions) {
        topics.set(topic, subscriptions = new Set());
    }
    subscriptions.add(subscriber);
    return () => { subscriptions!.delete(subscriber) };
}

/**
 * Publishes a message to all subscribers of a given topic.
 * The subscribers are informed in no particular order.
 */
function publish(topic: Topic, message: any): void {
    topics.get(topic)?.forEach(subscriber => {
        try {
            subscriber(message);
        } catch (err) {
            console.error("[pubsub] error publishing message:", err, "\n", { topic, message });
        }
    });
}