cqrs-eda/dist/observers/handler.js

Lightweight CQRS and Event-Driven Architecture library using TypeScript decorators, handlers and typings. Perfect for scalable event-driven apps.

import { getObserverRegistry } from "./decorators";
/**
 * Handles the registration and execution of observers for events.
 * Supports instantiation of observer classes, optionally via a custom factory.
 *
 * @template O - A mapping of event names to their payload types.
 */
export class ObserverHandler {
    /**
     * @param factory Optional factory function to instantiate observer classes.
     * This can be used to:
     * - Integrate with a dependency injection library, e.g., tsyringe or inversify.
     * - Customize instance creation with initialization logic.
     *
     * Example:
     * ```ts
     * const handler = new ObserverHandler((cls) => container.resolve(cls));
     * ```
     */
    constructor(factory) {
        this.factory = factory;
        // Map of event names to arrays of observer instances
        this.observers = new Map();
        const registry = getObserverRegistry();
        for (const [eventName, classes] of registry.entries()) {
            const instances = classes.map((cls) => this.factory ? this.factory(cls) : new cls());
            this.observers.set(eventName, instances);
        }
    }
    /**
     * Publishes an event to all registered observers.
     *
     * @param eventName - The event name to publish.
     * @param payload - The payload to send to each observer.
     * @throws Error if no observers are registered for the event.
     */
    async publish(eventName, payload) {
        const observers = this.observers.get(eventName);
        if (!observers || observers.length === 0) {
            throw new Error(`No observers registered for event "${String(eventName)}"`);
        }
        for (const observer of observers) {
            await observer.execute(payload);
        }
    }
    /**
     * Returns all events names registered.
     *
     */
    getRegisteredEventNames() {
        return Array.from(this.observers.keys());
    }
}