Script laves browser-sikket ?

Hvordan gør jeg dette script Browser-sikkert???

var nVal;
(function() {
    if (!navigator.cookieEnabled) return;
    if (document.cookie.indexOf("chart=")!=-1) {
        var aVal = document.cookie.split("chart=");
        if (aVal.length>1) {
            nVal = aVal[1].split(";")[0];
        }
        else setCook();
    }
    else setCook();

    function setCook() {
        var oExp = new Date(), nNewTime = oExp.getTime() + (1000*60*60*24*365);
        oExp.setTime(nNewTime);
        nVal = Math.round(Math.random()*10000000000);
        document.cookie="chart="+nVal+";expires=" + oExp.toGMTString();
    }
})();