publish subscribe in lwc code example

Example: publish and subscribe library in lwc

/**
 * A basic pub-sub mechanism for sibling component communication
 *
 * TODO - adopt standard flexipage sibling communication mechanism when it's available.
 */
 
const events = {};
 
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.
 */
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
};