advanced-events.js

function Event() {
  let subscribers = [];
  const subscribe = (...values) => {
    values.forEach((s) => { 
      if (typeof s === 'function') subscribers.push(s);
    });
  };
  const unsubscribe = (...values) => {
    values.forEach((v) => {
      if (subscribers.lastIndexOf(v) > -1) subscribers.splice(subscribers.lastIndexOf(v),1);
    });
  };
  const emit = function(...args) {
    const subscribersCopy = subscribers.slice();
    subscribersCopy.forEach((s) => s.apply(this, args));
    return args;
  };
  
  return {
    subscribe,
    unsubscribe,
    emit
  }
}