js根据当前日期 求一个月前 半年前 一年前的日期

   function p(s) {
        return s < 10 ? '0' + s: s;
}
getlastmonth() 
function getlastmonth() {
    var myDate = new Date();
    var currentYear=myDate.getFullYear();
    var currentMonth=myDate.getMonth()+1;  
    var lastMonth=myDate.getMonth();
    var currentDate=myDate.getDate();
    var lastDate;
    //一个月前的时间
    var prevCurrentYear=0;
    var prevCurrentMonth=0;
    var preDay = 0;
    //三个月前的时间
    var tmY =0;
    var tmM = 0;
    var tmD = 0;
    
    //半年前的时间
 var halfY =0;
 var halfM = 0;
 var halD = 0;
 
 //一年前的时间
 var oneY = 0;
 var oneM = 0;
 var oneD  = 0;
    var daysInMonth = new Array(0,31,28,31,30,31,30,31,31,30,31,30,31);
    isYears(currentYear);
 if(currentMonth==0){
     //一月前的时间
     prevCurrentYear=currentYear-1;
     prevCurrentMonth=12;
     isYears(prevCurrentYear)
     preDay = monthTime(prevCurrentMonth,currentDate)
     
     //三个月前的时间
     tmY = currentYear-1;
     tmM = 10;
     tmD = monthTime(tmM,currentDate);
     
     //半年前的时间
     halfY = currentYear-1;
     halfM = 6;
     halfD = monthTime(halfM,currentDate);
     
     //一年前的时间
      oneY = currentYear-1;
      oneM = 0;
      oneD = monthTime(oneM,currentDate);
     
 }else{
     //一个月前的时间
     prevCurrentYear=currentYear;
     prevCurrentMonth=isZero(currentMonth-1);
     preDay = monthTime(prevCurrentMonth,currentDate);
     
     //三个月前的时间
     if(currentMonth-3 < 0){
         tmY = currentYear-1;
         tmM = isZero(12+(currentMonth-3));
         isYears(tmY);
         tmD = monthTime(tmM,currentDate)
     }else{
         tmY = currentYear;
         tmM = isZero(currentMonth-3);
         isZero(tmM);
         isYears(tmY);
         tmD = monthTime(tmM,currentDate)
     }
     
     //半年前的时间
     if(currentMonth -6 < 3){
         halfY = currentYear-1;
         halfM = isZero(12+(currentMonth-6));
         isZero(halfM);
         isYears(halfM);
         halfD =monthTime(halfM,currentDate) 
     }else{
         halfY = currentYear;
         halfM = isZero(currentMonth-6);
         isZero(halfM);
         isYears(halfM);
         halfD =monthTime(halfM,currentDate) 
     }
     
     //一年前的时间
     oneY = currentYear-1;
     oneM =12+(currentMonth-12);
     isYears(halfM);
     oneD =monthTime(oneM,currentDate) 
 }
 function isYears(years){
     if(years%4 == 0 && years%100 != 0  || years%400 == 0 ){
            daysInMonth[2]= 29;
        }
 }
 function monthTime(a,b){
     if(daysInMonth[a] < b){
             lastDate =  daysInMonth[a]
        }else{
             lastDate = b;                
        }
     return lastDate;
 } 
 
 function isZero(s){
     if(s ==0 ){
         return s =12;
     }else{
         return s;
     }
 }
    var now=currentYear+'-'+p(currentMonth)+"-"+p(currentDate);
 var priceLastMonth = prevCurrentYear+"-"+p(prevCurrentMonth)+"-"+p(lastDate);
 //三个月前的时间
 var threeMonth = tmY + "-" + p(tmM) + '-' + p(tmD);
 
 //半年期的时间
 var halfTime = halfY +"-" + p(halfM) + "-" + p(halfD);
 
 //一年前的时间
 var oneTime = oneY + "-" + p(oneM) + "-" + p(oneD)
 var timeArr=[now,priceLastMonth,threeMonth,halfTime,oneTime]
 return timeArr;
}