pubsub for Experience Builder sites

pubsub.js

/**
 * Copyright (c) 2021.  7Summits Inc. All rights reserved.
 */

/**
 * A basic pub-sub mechanism for sibling component communication.
 * To be replaced by messageService when out of beta in experience builder:
 *
 * https://developer.salesforce.com/docs/component-library/documentation/en/lwc/lwc.use_message_channel
 * 
 * Reference: https://github.com/developerforce/pubsub/blob/master/force-app/main/default/lwc/pubsub/pubsub.js
 */

const events = {};

/**
 * Confirm that two page references have the same attributes
 * @param {object} pageRef1 - The first page reference
 * @param {object} pageRef2 - The second page reference
 */
const samePageRef = (pageRef1, pageRef2) => {
	const obj1 = pageRef1.attributes;
	const obj2 = pageRef2.attributes;
	return Object.keys(obj1)
		.concat(Object.keys(obj2))
		.every(key => {
			return obj1[key] === obj2[key];
		});
};

/**
 * Registers a callback for an event
 * @param {string} eventName - Name of the event to listen for.
 * @param {function} callback - Function to invoke when said event is fired.
 * @param {object} thisArg - The value to be passed as the this parameter to the callback function is bound.
 *
 * PageRef Example:
 *
 * import { CurrentPageReference } from 'lightning/navigation';
 * @wire(CurrentPageReference) pageRef;
 *
 */
const registerListener = (eventName, callback, thisArg) => {
	// Checking that the listener has a pageRef property. We rely on that property for filtering purpose in fireEvent()
	if (!thisArg.pageRef) {
		throw new Error(
			'pubsub listeners need a "@wire(CurrentPageReference) pageRef" property'
		);
	}
	
	if (!events[eventName]) {
		events[eventName] = [];
	}
	const duplicate = events[eventName].find(listener => {
		return listener.callback === callback && listener.thisArg === thisArg;
	});
	if (!duplicate) {
		events[eventName].push({ callback, thisArg });
	}
};

/**
 * Unregisters a callback for an event
 * @param {string} eventName - Name of the event to unregister from.
 * @param {function} callback - Function to unregister.
 * @param {object} thisArg - The value to be passed as the this parameter to the callback function is bound.
 */
const unregisterListener = (eventName, callback, thisArg) => {
	if (events[eventName]) {
		events[eventName] = events[eventName].filter(
			listener =>
				listener.callback !== callback || listener.thisArg !== thisArg
		);
	}
};

/**
 * Unregisters all event listeners bound to an object.
 * @param {object} thisArg - All the callbacks bound to this object will be removed.
 */
const unregisterAllListeners = thisArg => {
	Object.keys(events).forEach(eventName => {
		events[eventName] = events[eventName].filter(
			listener => listener.thisArg !== thisArg
		);
	});
};

/**
 * Fires an event to listeners.
 * @param {object} pageRef - Reference of the page that represents the event scope.
 * @param {string} eventName - Name of the event to fire.
 * @param {*} payload - Payload of the event to fire.
 */
const fireEvent = (pageRef, eventName, payload) => {
	if (events[eventName]) {
		const listeners = events[eventName];
		listeners.forEach(listener => {
			if (samePageRef(pageRef, listener.thisArg.pageRef)) {
				try {
					listener.callback.call(listener.thisArg, payload);
				} catch (error) {
					// fail silently
				}
			}
		});
	}
};

export {
	registerListener,
	unregisterListener,
	unregisterAllListeners,
	fireEvent
};