pubsub.js

function pubsubFactory() {
  let subscribers = [];
  const pub = publish;
  const sub = subscribe;
  const remove = unsubscribe;

  function publish(message) {
    if (!message) {
      throw new Error('Not going to publish an empty message to subscribers.', 'pubsub.js');
    }

    subscribers
      .forEach(x => x.fn(message));
  }

  function subscribe(fn) {
    if (!fn || typeof fn !== 'function') {
      throw new Error('Subscribe requires a Function as a subscription.', 'pubsub.js');
    }
    
    const id = Symbol(fn);

    subscribers
      .push({fn, id});
      
    return id;
  }

  function unsubscribe(id) {
    if (!id) {
      throw new Error('An identifier is required for removing a subscription.', 'pubsub.js');
    }

    subscribers = subscribers
      .filter(x => x.id !== id);
  }

  return {
      publish,
      subscribe,
      unsubscribe,
      pub,
      sub,
      remove
    };
}

export default pubsubFactory;