cetra/lib/core/Emitter.js

class Emitter {
	#listeners;
	constructor() {
		this.#listeners = new Map();
	}

	/**
	 * Registers a callback function for the specified event.
	 *
	 * @param {string} event - The name of the event.
	 * @param {Function} callback - The callback function to be executed when the event is triggered.
	 */
	on(event, callback) {
		if (!this.#listeners.has(event)) {
			this.#listeners.set(event, new Set());
		}
		this.#listeners.get(event).push(callback);
	}

	/**
	 * Removes an event listener callback for the specified event.
	 * If no callback is provided, removes all callbacks for the event.
	 *
	 * @param {string} event - The name of the event.
	 * @param {Function} [callback] - The callback function to be removed.
	 */
	off(event, callback = undefined) {
		if (typeof event != 'string') return;

		if (!this.#listeners.has(event)) return false;

		if (!callback || this.#listeners.get(event).size === 0) {
			return this.#listeners.delete(event);
		}

		this.#listeners.get(event).delete(callback);
	}

	/**
	 * Emits an event and invokes all registered listeners for that event.
	 *
	 * @param {string} event - The name of the event to emit.
	 * @param {...any} args - The arguments to pass to the event listeners.
	 */
	emit(event, ...args) {
		if (!this.#listeners.has(event)) {
			return;
		}

		for (const callback of [...this.#listeners.get(event)]) {
			callback(this, ...args);
		}
	}
}

export default Emitter;