Simple PubSub implementation

functional-pubsub.js

const pubSub = () => {
  // The core of our pubsub implementation
  const subscriptions = {}
  
  // Stupid naive way to generate an ID for each subscription.
  // Should really be something more robust, but this is a simple implementation after all
  const generateID = () => Math.floor(Math.random() * 100);
  
  // Publish handler. Runs all the callbacks for a given eventName
  const publish = (eventName, data) => subscriptions[eventName] && subscriptions[eventName].map(subscription => subscription.callback(...data));
  
  // Subscribe Handler. Adds a subscriber for an event, with an ID so we can unsubscribe each unique subscriber
  const subscribe = (eventName, callback) => {
    const eventID = generateID();

    // If there's no existing subscriptions, create an empty array for it.
    if(!subscriptions[eventName]) {
      subscriptions[eventName] = []
    }

    // Push the subscriber to the event array
    subscriptions[eventName].push({id: eventID, callback});
    
    // Return an unsubscribe function.
    return () => subscriptions[eventName] = subscriptions[eventName].filter(event => event.id !== eventID)
  }

  // Method for clearing all subscribers from an event
  const clearSubscribers = (eventName) => subscriptions[eventName] = []

  return {
    publish,
    subscribe,
    clearSubscribers,
  }
}