parallel-universe/PubSub.mjs

The set of async flow control structures and promise utils.

import { AbortablePromise } from './AbortablePromise.mjs';

/**
 * Publish–subscribe pattern implementation that guarantees the delivery of published messages even if any of listeners
 * would throw an error.
 *
 * @template T The published message.
 */
class PubSub {
    constructor() {
        this._listeners = [];
    }
    /**
     * The number of subscribed listeners.
     */
    get listenerCount() {
        return this._listeners.length;
    }
    /**
     * Synchronously invokes listeners with the published message.
     *
     * @param message The published message.
     */
    publish(message) {
        for (const listener of this._listeners.slice(0)) {
            try {
                listener(message);
            }
            catch (error) {
                setTimeout(() => {
                    // Force uncaught exception
                    throw error;
                }, 0);
            }
        }
    }
    /**
     * Waits for a message that satisfies the given predicate to be published and resolves with that message.
     *
     * @param predicate A function that takes the message as a parameter and returns true if the message satisfies the condition, otherwise false.
     * @returns An {@link AbortablePromise} that resolves with the published message that satisfies the predicate.
     */
    waitFor(predicate) {
        return new AbortablePromise((resolve, _reject, signal) => {
            const unsubscribe = this.subscribe(message => {
                if (predicate(message)) {
                    resolve(message);
                    unsubscribe();
                }
            });
            signal.addEventListener('abort', unsubscribe);
        });
    }
    /**
     * Adds a listener that would receive all messages published via {@link publish}.
     *
     * @param listener The callback.
     * @returns The callback that unsubscribes the listener.
     */
    subscribe(listener) {
        if (this._listeners.indexOf(listener) === -1) {
            this._listeners.push(listener);
        }
        return () => this.unsubscribe(listener);
    }
    /**
     * Unsubscribes a listener.
     *
     * @param listener The callback that was previously {@link subscribe subscribed}.
     */
    unsubscribe(listener) {
        const index = this._listeners.indexOf(listener);
        if (index !== -1) {
            this._listeners.splice(index, 1);
        }
    }
    /**
     * Unsubscribes all listeners.
     */
    unsubscribeAll() {
        this._listeners = [];
    }
}

export { PubSub };