var MessageBus = function() {
  this.subscribers = [];
};

MessageBus.prototype.subscribe = function (topic, myCallback) {
  this.subscribers[topic] = this.subscribers[topic] || []
  this.subscribers[topic].push(myCallback);
};

MessageBus.prototype.publish = function (topic, payload) {
  this.subscribers[topic].forEach((cb) => {
    cb(payload);
  })
};

var messageBus = new MessageBus('new_signup');

messageBus.subscribe('new_signup', function(payload) {
  console.log(payload);
});

messageBus.subscribe('another_topic', function(payload) {
  console.log('new payload', payload);
});

messageBus.publish('new_signup', {'foo': 'bar', 'goo': 'gar'} );
messageBus.publish('new_signup', {'asd': 'asd', 'vb': 'xcv'} );

messageBus.publish('another_topic', {'asd': 'asd', 'vb': 'xcv'} );