Design a pub sub pattern in vanilla JS

// publisher// Subscriber// unsubscribe// Some place to store callbacks that are registered from subscribers.function pubSub() {  // object which will track of all events and subscription  const subscribers = {}  // Publisher:   function publish(eventName, data) {    // return if event is not subscribed    if (!Array.isArray(subscribers[eventName])) {      return    }    // Whenever you publish any event, it will trigger callback for all stored event in subscriber object    subscribers[eventName].forEach((callback) => {      callback(data)    })  }  // Subscriber  function subscribe(eventName, callback) {    if (!Array.isArray(subscribers[eventName])) {      subscribers[eventName] = []    }    //on subscribe we will we will push callback to subscribers[eventName] array    subscribers[eventName].push(callback);    const index = subscribers[eventName].length - 1    // subscribed callbacks to be removed when they are no longer necessary.    return {      unsubscribe() {        subscribers[eventName].splice(index, 1);      },    }  }  return {    publish,    subscribe,  }}