JavaScript Observer Pattern

var Users = {
list: [],
listeners: {},
add: function(name) {
this.list.push({name: name});
this.dispatch("user-added");
},
on: function(eventName, listener) {
if(!this.listeners[eventName]) this.listeners[eventName] = [];
this.listeners[eventName].push(listener);
},
dispatch: function(eventName) {
if(this.listeners[eventName]) {
for(var i=0; i<this.listeners[eventName].length; i++) {
this.listeners[eventName][i](this);
}
}
},
numOfAddedUsers: function() {
return this.list.length;
}
}

Users.on("user-added", function(obj) {
alert(Users.numOfAddedUsers());
console.log("obj:",obj);
});

Users.add("Krasimir");
Users.add("Tsonev");