Permission file and folder in Magento

sudo find /var/www/html/magentoInstallationFolder/ -type d -exec chmod 775 {} \;

sudo find /var/www/html/magentoInstallationFolder/ -type f -exec chmod 664 {} \;

sudo find -type d -exec chmod 775 {} \;

sudo find -type f -exec chmod 664 {} \;

Set Writable for 3 folders in root magento: var, media, app/etc
sudo chmod -R 777 var/  media/ app/etc/ downloader/

Done. Good Luck!

==== Magento UseGuide ====

find . -type f -exec chmod 400 {} \;
find . -type d -exec chmod 500 {} \; 
find var/ -type f -exec chmod 600 {} \; 
find media/ -type f -exec chmod 600 {} \;
find var/ -type d -exec chmod 700 {} \; 
find media/ -type d -exec chmod 700 {} \;
chmod 700 includes
chmod 600 includes/config.php

Store Session in Javascript

File session.js

/**
 * Implements cookie-less JavaScript session variables
 * v1.0
 *
 * By Craig Buckler, Optimalworks.net
 *
 * As featured on SitePoint.com
 * Please use as you wish at your own risk.
 *
 * Usage:
 *
 * // store a session value/object
 * Session.set(name, object);
 *
 * // retreive a session value/object
 * Session.get(name);
 *
 * // clear all session data
 * Session.clear();
 *
 * // dump session data
 * Session.dump();
 */

if (JSON && JSON.stringify && JSON.parse) var Session = Session || (function() {

    // window object
    var win = window.top || window;

    // session store
    var store = (win.name ? JSON.parse(win.name) : {});

    // save store on page unload
    function Save() {
        win.name = JSON.stringify(store);
    };

    // page unload event
    if (window.addEventListener) window.addEventListener("unload", Save, false);
    else if (window.attachEvent) window.attachEvent("onunload", Save);
    else window.onunload = Save;

    // public methods
    return {

        // set a session variable
        set: function(name, value) {
            store[name] = value;
        },

        // get a session value
        get: function(name) {
            return (store[name] ? store[name] : undefined);
        },

        // clear session
        clear: function() { store = {}; },

        // dump session data
        dump: function() { return JSON.stringify(store); }

    };

})();

========================================

File json-serial.js

/**
 * Implements JSON stringify and parse functions
 * v1.0
 *
 * By Craig Buckler, Optimalworks.net
 *
 * As featured on SitePoint.com
 * Please use as you wish at your own risk.
 *
 * Usage:
 *
 * // serialize a JavaScript object to a JSON string
 * var str = JSON.stringify(object);
 *
 * // de-serialize a JSON string to a JavaScript object
 * var obj = JSON.parse(str);
 */

var JSON = JSON || {};

// implement JSON.stringify serialization
JSON.stringify = JSON.stringify || function (obj) {

    var t = typeof (obj);
    if (t != "object" || obj === null) {

        // simple data type
        if (t == "string") obj = '"'+obj+'"';
        return String(obj);

    }
    else {

        // recurse array or object
        var n, v, json = [], arr = (obj && obj.constructor == Array);

        for (n in obj) {
            v = obj[n]; t = typeof(v);

            if (t == "string") v = '"'+v+'"';
            else if (t == "object" && v !== null) v = JSON.stringify(v);

            json.push((arr ? "" : '"' + n + '":') + String(v));
        }

        return (arr ? "[" : "{") + String(json) + (arr ? "]" : "}");
    }
};


// implement JSON.parse de-serialization
JSON.parse = JSON.parse || function (str) {
    if (str === "") str = '""';
    eval("var p=" + str + ";");
    return p;
};

=========================

var firstTime = Session.get("firstTime") || {
    first: true
};

if (firstTime.first == true) {
 console.log("lan dau");
 Session.set("firstTime", {first: false});
}
else {
 console.log("lan n");
 Session.clear();
}