JS获取上个月(转)

1.yyyy-mm-dd获取上个月

function getUpMonth(t){
    var tarr = t.split('-');
    var year = tarr[0];                //获取当前日期的年
    var month = tarr[1];            //获取当前日期的月
    var day = tarr[2];                //获取当前日期的日
    var days = new Date(year,month,0);
    days = days.getDate();//获取当前日期中的月的天数
    var year2 = year;
    var month2 = parseInt(month)-1;
    if(month2==0) {
        year2 = parseInt(year2)-1;
        month2 = 12;
    }
    var day2 = day;
    var days2 = new Date(year2,month2,0);
    days2 = days2.getDate();
    if(day2>days2) {
        day2 = days2;
    }
    if(month2<10) {
        month2 = '0'+month2;
    }
    var t2 = year2+'-'+month2+'-'+day2;
    return t2;
}

2.yyyymm获取上个月

function getUpMonth(t){
    var year =t.substring(0,4);            //获取当前日期的年
    var month = t.substring(4,6);              //获取当前日期的月

    var year2 = year;
    var month2 = parseInt(month)-1;
    if(month2==0) {
        year2 = parseInt(year2)-1;
        month2 = 12;
    }

    if(month2<10) {
        month2 = '0'+month2;
    }
    var m = year2.toString();
    var n= month2.toString();
    var t2 = m+n;
    return t2;
}