Cohort Anarisis in Google Analytics

ga-cohort.js

    try {
        var f = function (d) {
            return d.getFullYear() + ("0" + (d.getMonth() + 1)).slice(-2) + ("0" + d.getDate()).slice(-2);
        };
        var c = document.cookie;
        var i = c.indexOf('__utma');
        var s = null;
        if (i < 0) { 
            s = f(new Date());
        } else {
            var utma = c.substring(i, c.indexOf(';', i));
            if (utma) {
                var v = utma.split('.');
                if (v[2]) {
                    var date = new Date();
                    date.setTime(v[2] * 1000);
                    s = f(date);
                }
            }
        }
        if(s) {
            _gaq.push(['_setCustomVar', 1, 'FirstVisit', s, 1]);
        }
    } catch (e) {
    }