js 獲取當前日期或者前、後N天yyyy-MM-dd的方法

//js獲取當前日期、當前日期前、後N天的標準年月日

//day=0爲當前天，day=7爲前7天，day=-7爲當前日期的後7天

function getstartdate(day) {
            var beginDate;
            var curr_time = new Date();
            var week_time = new Date(curr_time.getTime() - 1000 * 60 * 60 * 24 * day);
            var curyear = week_time.getFullYear();
            var curmonth = week_time.getMonth() + 1;
            curmonth = curmonth > 9 ? curmonth.toString() : '0' + curmonth.toString();
            var curday = week_time.getDate();
            curday = curday > 9 ? curday.toString() : '0' + curday.toString();
            beginDate = curyear + "-" + curmonth + "-" + curday;
            return beginDate
        }