uhateoas
8/19/2013 - 1:56 PM

Observer Pattern Wherever you see subscription or dispatching of events, you'll likely see this pattern. There are observers which are inte

Observer Pattern

Wherever you see subscription or dispatching of events, you'll likely see this pattern. There are observers which are interested in something related to a specific object. Once the action occurs, the object notifies the observers. The example below shows how we can add an observer to the Users object:

observer-pattern.js
content_copyfile_download
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() {
    alert(Users.numOfAddedUsers());
});
 
Users.add("Krasimir");
Users.add("Tsonev");