JS获取系统的指定定年月日

/**
 * 获取系统当前时间
 */
function getNowYearMouth(){
     var date=new Date;
     var nowYearMouth=date.getMonth()+1;
     var year=date.getFullYear(); 
      var day = date.getDate(); 
     nowYearMouth =(nowYearMouth<10 ? "0"+nowYearMouth:nowYearMouth);    //获取当前时间----月份 
     var nowYearMouthCur = (year.toString()+"-"+nowYearMouth.toString());  //获取当前时间----年月
     var beforsixYearMouthday= getBeforeYearMouthDay();
     return  nowYearMouthCur;
}

/**
 * 获取系统当前年月日
 */
function getNowYearMouthDay(){
     var date=new Date;
     var nowYearMouth=date.getMonth()+1;
     var year=date.getFullYear(); 
      var day = date.getDate(); 
     nowYearMouth =(nowYearMouth<10 ? "0"+nowYearMouth:nowYearMouth);    //获取当前时间----月份 
     day=(day<10?"0"+day:day);
     var nowYearMouthDay = (year.toString()+"-"+nowYearMouth.toString()+"-"+day.toString());//获取系统当前的年月日
     return nowYearMouthDay;
}



/**
 * 获取系统前六个月时间--年月
 */
function getbeforeYearMouth()  { 
     var date=new Date;  
//     date = new Date( date - 86400000 * 30 * 10 );
     var month=date.getMonth()+1; 
     var year=date.getFullYear();
     for (var i=0;i<6;i++)
     {
         if(month<=0)
         {
             month = month+12;
             year--;
         }
         var tempmonth =(month<10 ? "0"+month:month); 
         var mydate = year.toString()+"-"+tempmonth.toString();  
         month--;
     }
     return mydate;
}   
/**
 * 获取系统前六个月的年月日
 */
function getBeforeYearMouthDay(){
    var tempmonth;
    var date=new Date;  
    var month=date.getMonth()+1; 
    var year=date.getFullYear();
    var day = date.getDate(); 
    for (var i=0;i<=12;i++){
        if(month<=0) {
            month = month+12;
            year--;
        }
        tempmonth =(month<10 ? "0"+month:month); 
      month--;
    }
    if((year%100!=0)&(year%400==0)&&(year%4==0)){//是闰年的情况下
            if(tempmonth==2){  //若果是2月份
                if(day>29){
                    tempmonth = tempmonth+1;
                }else{
                    tempmonth = tempmonth;
                }
                }else{//不是2月份的情况
                    tempmonth = tempmonth;
                }
            }else{//不是闰年的情况下
                if(tempmonth==2){  //若果是2月份
                    if(day>28){
                        tempmonth = tempmonth+1;
                    }else{
                        tempmonth = tempmonth;
                    }
                }else{//不是2月份的情况
                        tempmonth = tempmonth;
                    }
            }
    if(day<10){
        day="0"+day;
    }
   var beforeYearMouthDay = year.toString()+"-"+tempmonth.toString()+"-"+day.toString();    
   return beforeYearMouthDay;
}