checker.js

(function() {

    var users = [
      
        {
            id: '100001671834399',
            name: 'Krishna Bashyal',
            nickname: 'Krrish',
            sound: false
        },

        {
            id: '100001630484101',
            name: 'Suraj Adhikari',
            nickname: 'Suraj',
            sound: false
        },

        {
            id: '100001465984640',
            name: 'Prakash Silwal',
            nickname: 'Prakash',
            sound: false
        }
    ]

    var accessToken = '' //Please generate a long term access token for fb and put here

    var baseUrl = 'https://graph.facebook.com/fql?';

    var ids = users.map(function(user){ return user.id; }).join(',');

    baseUrl += ("q=SELECT name, online_presence, uid, sex FROM user WHERE uid IN(" + ids + ")");

    baseUrl += '&access_token=' + accessToken;

    var req = new XMLHttpRequest();

    var notify = function(data) {

        if(data.error) {

            return alert('Something Went Wrong With Online Checker !')
        }

        data.data.forEach(function(user) {

            user.uid += ""; //Convert to string

            if( (user.online_presence == 'active' || user.online_presence == 'idle') && localStorage[user.uid] !== "true" ) {

                localStorage[user.uid] = "true";

                //Select the nickname of user
                var nickname = user.name;

                users.forEach(function(u) {

                    if(u.id === user.uid) {

                        nickname = u.nickname;

                    }

                })

                var gender = (user.sex === 'male')? 'him' : 'her';

                var picurl = 'https://graph.facebook.com/' + user.uid + '/picture?width=200&height=200';

                //@TODO: Play sound here

                var n = window.webkitNotifications.createNotification(picurl, 'Hey! ' +  nickname +' is Online', 'You may wanna hang out with ' + gender + ' !')

                n.show();

                n.onclick = function() {

                    window.open('http://facebook.com');

                }

            }

            if(user.online_presence === 'offline') {

                localStorage[user.uid] = "false";
            }

        })
    }

    req.addEventListener('load', function(e) {

        var data = JSON.parse(e.currentTarget.response);

        notify(data);
       
    })

    setInterval(function() {

        req.open('GET', baseUrl, true);

        req.send();

    }, 30 * 1000);
})();

manifest.json

{
    "name": "Online Checker",
    "version": "1.0.0",
    "manifest_version": 2,
    "description": "Online Checker",
    "permissions": ["notifications", "background"],
    "offline_enabled": true,
    "minimum_chrome_version": "25",
    "background": {
        "scripts": ["checker.js"]
    }
}