js獲取時間(上一個季度)

function getLastQuarter(){
        var today = new Date();   
        var dayMSec = 24 * 3600 * 1000; 
        //得到上一個季度的第一天    
        var lastQuarterFirstDay = new Date(today.getFullYear() , today.getMonth() - 3 , 1);    
        //得到本月第一天    
        var nowMonthFirstDay = new Date(today.getFullYear() , today.getMonth(), 1);    
        //得到上一個季度的最後一天的毫秒值    
        var lastQuarterLastDayMSec = nowMonthFirstDay.getTime() - 1 * dayMSec;    
        var lastQuarterLastDay = new Date(lastQuarterLastDayMSec);    
            
        return lastQuarterFirstDay.format('yyyy-MM-dd') +","+lastQuarterLastDay.format('yyyy-MM-dd');    
    }