function getLastMonth(){//獲取上個月日期
    var date = new Date; 
    var year = date.getFullYear();
    var month = date.getMonth();
    if(month == 0){
         year = year -1;
         month = 12; 
    }
    return year+"年"+month+"月";
}

/**
 * 獲取上個月月底日期
 */
function getLastMonthAndDay(){
    var nowDate = new Date();
    var year = nowDate.getFullYear();
    var month = nowDate.getMonth();
    if(month == 0){
        month = 12;
        year = year - 1;
    }
    var lastDay = new Date(year,month,0);
    var yyyyMMdd = year+"年"+month+"月"+lastDay.getDate()+"日";
    console.log(yyyyMMdd);
}