JS中给指定时间增加月份

function addMonth(){     var date = "2018-11-30 23:59:59";     //var date = "2018-11-30";     var addNum = "3";     var num = parseInt(addNum);     var d=new Date(date);           var thisMonth = d.getMonth()+1;     var thisYear = d.getFullYear();     var thisDay = d.getDate();     var thisHour = d.getHours();     var thsiMinu = d.getMinutes();     var thisSecon = d.getSeconds();          var addCount = thisMonth + num;     var diffMonthCount = parseInt(addCount/12);    //取整          if((thisMonth + num) == 12*diffMonthCount){    //如果是本年         if((thisMonth + num) == 12){             diffMonthCount = 0;         }else{             diffMonthCount = diffMonthCount-1;         }     }     if(thisMonth + num > 12){    //如果是大于一年         thisYear += diffMonthCount;     }     thisMonth = (addCount)-12*diffMonthCount;     if(thisMonth < 10){         thisMonth = "0"+thisMonth;     }     if(thisHour < 10){         thisHour = "0"+thisHour;     }     if(thsiMinu < 10){         thsiMinu = "0"+thsiMinu;     }     if(thisSecon < 10){         thisSecon = "0"+thisSecon;     }          var thatDate = new Date(thisYear,thisMonth,0); //当天数为0 js自动处理为上一月的最后一天     var thatDay = thatDate.getDate();//指定年月的当月最大天数          var diffDay = thatDay - thisDay;     if((thatDay - thisDay) > 0 || (thatDay - thisDay) < 0){         thisDay = thatDay;     }     var dateStr = "";     if(thsiMinu == 0 && thisSecon == 0){         dateStr = thisYear + "-" + thisMonth + "-" + thisDay;     }else{         dateStr = thisYear + "-" + thisMonth + "-" + thisDay +" " +thisHour+":"+ thsiMinu+":"+thisSecon;     }     return dateStr;      }