Observer pattern // source http://jsbin.com/daquqiq

jsbin.daquqiq.js

console.clear();

var Subject = function() {
  var self = this;
  self.observers = [];

  return {
    subscribe: function(observer) {
      self.observers.push(observer);
    },
    unsubscribe: function(observer) {
      var index = self.observers.indexOf(observer);
      if (index > -1) {
        self.observers.splice(index, 1);
      }
    },
    notify: function(observer) {
      var index = self.observers.indexOf(observer);
      if (index > -1) {
        self.observers[index].notify(index);
      }
    },
    notifyAll: function() {
      for (var i = 0; i < self.observers.length; i++) {
        self.observers[i].notify(i);
      }
    }
  };
};


var Observer = function() {
  return {
    notify: function(index) {
      console.log("Observer " + index + " is notified!");
    }
  }
}


  var subject = new Subject();
  
  var observer1 = new Observer();
  var observer2 = new Observer();
  var observer3 = new Observer();
  var observer4 = new Observer();

  subject.subscribe(observer1);  
  subject.subscribe(observer2);  
  subject.subscribe(observer3);
  subject.subscribe(observer4);

  subject.notifyAll();

  subject.notify(observer3);