js得到本周和下周的日期（在線等）,该如何处理

 //获取日期差        function getDate(date, dayspan)        {            var time = date.valueOf();            time += (dayspan * 24 * 60 * 60 * 1000);            return new Date(time);        }                // w为0为当前周,1为下周        function getWeek(w)        {            var date = new Date();            var x = date.getDay();            var msg = "";                        var weekFirst = getDate(date, w * 7 - x);            var weekLast = getDate(date, 6 - x + w * 7);            msg = weekFirst.getFullYear() + "-" + eval(weekFirst.getMonth() + 1) + "-" + weekFirst.getDate();            msg += "___" + weekLast.getFullYear() + "-" + eval(weekLast.getMonth() + 1) + "-" + weekLast.getDate();                        return msg;        }        alert(getWeek(0));        alert(getWeek(1));