The source code

    /**
     * @class Ext.state.CookieProvider
     * @extends Ext.state.Provider
     * The default Provider implementation which saves state via cookies.
     * <br />Usage:
     <pre><code>
       var cp = new Ext.state.CookieProvider({
           path: "/cgi-bin/",
           expires: new Date(new Date().getTime()+(1000*60*60*24*30)), //30 days
           domain: "extjs.com"
       });
       Ext.state.Manager.setProvider(cp);
     </code></pre>
     * @cfg {String} path The path for which the cookie is active (defaults to root '/' which makes it active for all pages in the site)
     * @cfg {Date} expires The cookie expiration date (defaults to 7 days from now)
     * @cfg {String} domain The domain to save the cookie for.  Note that you cannot specify a different domain than
     * your page is on, but you can specify a sub-domain, or simply the domain itself like 'extjs.com' to include
     * all sub-domains if you need to access cookies across different sub-domains (defaults to null which uses the same
     * domain the page is running on including the 'www' like 'www.extjs.com')
     * @cfg {Boolean} secure True if the site is using SSL (defaults to false)
     * @constructor
     * Create a new CookieProvider
     * @param {Object} config The configuration object
     */
    Ext.state.CookieProvider = Ext.extend(Ext.state.Provider, {

        constructor : function(config){
            Ext.state.CookieProvider.superclass.constructor.call(this);
            this.path = "/";
            this.expires = new Date(new Date().getTime()+(1000*60*60*24*7)); //7 days
            this.domain = null;
            this.secure = false;
            Ext.apply(this, config);
            this.state = this.readCookies();
        },

        // private
        set : function(name, value){
            if(typeof value == "undefined" || value === null){
                this.clear(name);
                return;
            }
            this.setCookie(name, value);
            Ext.state.CookieProvider.superclass.set.call(this, name, value);
        },

        // private
        clear : function(name){
            this.clearCookie(name);
            Ext.state.CookieProvider.superclass.clear.call(this, name);
        },

        // private
        readCookies : function(){
            var cookies = {},
                c = document.cookie + ";",
                re = /\s?(.*?)=(.*?);/g,
        	    matches,
                name,
                value;
        	while((matches = re.exec(c)) != null){
                name = matches[1];
                value = matches[2];
                if(name && name.substring(0,3) == "ys-"){
                    cookies[name.substr(3)] = this.decodeValue(value);
                }
            }
            return cookies;
        },

        // private
        setCookie : function(name, value){
            document.cookie = "ys-"+ name + "=" + this.encodeValue(value) +
               ((this.expires == null) ? "" : ("; expires=" + this.expires.toGMTString())) +
               ((this.path == null) ? "" : ("; path=" + this.path)) +
               ((this.domain == null) ? "" : ("; domain=" + this.domain)) +
               ((this.secure == true) ? "; secure" : "");
        },

        // private
        clearCookie : function(name){
            document.cookie = "ys-" + name + "=null; expires=Thu, 01-Jan-70 00:00:01 GMT" +
               ((this.path == null) ? "" : ("; path=" + this.path)) +
               ((this.domain == null) ? "" : ("; domain=" + this.domain)) +
               ((this.secure == true) ? "; secure" : "");
        }
    });