The source code

    /**
     * @class Ext.util.Cookies
     * Utility class for managing and interacting with cookies.
     * @singleton
     */
    Ext.util.Cookies = {
        /**
         * Create a cookie with the specified name and value. Additional settings
         * for the cookie may be optionally specified (for example: expiration,
         * access restriction, SSL).
         * @param {String} name The name of the cookie to set.
         * @param {Mixed} value The value to set for the cookie.
         * @param {Object} expires (Optional) Specify an expiration date the
         * cookie is to persist until.  Note that the specified Date object will
         * be converted to Greenwich Mean Time (GMT).
         * @param {String} path (Optional) Setting a path on the cookie restricts
         * access to pages that match that path. Defaults to all pages (<tt>'/'</tt>).
         * @param {String} domain (Optional) Setting a domain restricts access to
         * pages on a given domain (typically used to allow cookie access across
         * subdomains). For example, "extjs.com" will create a cookie that can be
         * accessed from any subdomain of extjs.com, including www.extjs.com,
         * support.extjs.com, etc.
         * @param {Boolean} secure (Optional) Specify true to indicate that the cookie
         * should only be accessible via SSL on a page using the HTTPS protocol.
         * Defaults to <tt>false</tt>. Note that this will only work if the page
         * calling this code uses the HTTPS protocol, otherwise the cookie will be
         * created with default options.
         */
        set : function(name, value){
            var argv = arguments;
            var argc = arguments.length;
            var expires = (argc > 2) ? argv[2] : null;
            var path = (argc > 3) ? argv[3] : '/';
            var domain = (argc > 4) ? argv[4] : null;
            var secure = (argc > 5) ? argv[5] : false;
            document.cookie = name + "=" + escape(value) + ((expires === null) ? "" : ("; expires=" + expires.toGMTString())) + ((path === null) ? "" : ("; path=" + path)) + ((domain === null) ? "" : ("; domain=" + domain)) + ((secure === true) ? "; secure" : "");
        },

        /**
         * Retrieves cookies that are accessible by the current page. If a cookie
         * does not exist, <code>get()</code> returns <tt>null</tt>.  The following
         * example retrieves the cookie called "valid" and stores the String value
         * in the variable <tt>validStatus</tt>.
         * <pre><code>
         * var validStatus = Ext.util.Cookies.get("valid");
         * </code></pre>
         * @param {String} name The name of the cookie to get
         * @return {Mixed} Returns the cookie value for the specified name;
         * null if the cookie name does not exist.
         */
        get : function(name){
            var arg = name + "=";
            var alen = arg.length;
            var clen = document.cookie.length;
            var i = 0;
            var j = 0;
            while(i < clen){
                j = i + alen;
                if(document.cookie.substring(i, j) == arg){
                    return Ext.util.Cookies.getCookieVal(j);
                }
                i = document.cookie.indexOf(" ", i) + 1;
                if(i === 0){
                    break;
                }
            }
            return null;
        },

        /**
         * Removes a cookie with the provided name from the browser
         * if found by setting its expiration date to sometime in the past.
         * @param {String} name The name of the cookie to remove
         */
        clear : function(name){
            if(Ext.util.Cookies.get(name)){
                document.cookie = name + "=" + "; expires=Thu, 01-Jan-70 00:00:01 GMT";
            }
        },
        /**
         * @private
         */
        getCookieVal : function(offset){
            var endstr = document.cookie.indexOf(";", offset);
            if(endstr == -1){
                endstr = document.cookie.length;
            }
            return unescape(document.cookie.substring(offset, endstr));
        }
    };