js 获取当前日期或者前、后N天yyyy-MM-dd的方法

//js获取当前日期、当前日期前、后N天的标准年月日

//day=0为当前天，day=7为前7天，day=-7为当前日期的后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
        }