js如何获取前几个月或后几个月时间

 /** ????*获取几个月前的输入日期 ????*{param:DateTime} date 输入日期(YYYY-MM-DD) ????*{param:number } monthNum 月数 ????*/ ????function GetPreMonthDay(date, monthNum) { ????????var dateArr = date.split(‘-‘); ????????var year = dateArr[0]; //获取当前日期的年份 ????????var month = dateArr[1]; //获取当前日期的月份 ????????var day = dateArr[2]; //获取当前日期的日 ????????var days = new Date(year, month, 0); ????????days = days.getDate(); //获取当前日期中月的天数 ????????var year2 = year; ????????var month2 = parseInt(month) - monthNum; ????????if (month2 <= 0) { ????????????var absM = Math.abs(month2); ????????????year2 = parseInt(year2) - Math.ceil(absM / 12 == 0 ? 1 : parseInt(absM) / 12); ????????????month2 = 12 - (absM % 12); ????????} ????????var day2 = day; ????????var days2 = new Date(year2, month2, 0); ????????days2 = days2.getDate(); ????????if (day2 > days2) { ????????????day2 = days2; ????????} ????????if (month2 < 10) { ????????????month2 = ‘0‘ + month2; ????????} ????????var t2 = year2 + ‘-‘ + month2 + ‘-‘ + day2; ????????return t2; ????} ????/** ????*获取下一个月的输入日期 ????*{param:DateTime} date 输入日期(YYYY-MM-DD) ????*{param:number } monthNum 月数 ????*/ ????function GetNextMonthDay(date, monthNum) { ????????var dateArr = date.split(‘-‘); ????????var year = dateArr[0]; //获取当前日期的年份 ????????var month = dateArr[1]; //获取当前日期的月份 ????????var day = dateArr[2]; //获取当前日期的日 ????????var days = new Date(year, month, 0); ????????days = days.getDate(); //获取当前日期中的月的天数 ????????var year2 = year; ????????var month2 = parseInt(month) + parseInt(monthNum); ????????if (month2 > 12) { ????????????year2 = parseInt(year2) + parseInt((parseInt(month2) / 12 == 0 ? 1 : parseInt(month2) / 12)); ????????????month2 = parseInt(month2) % 12; ????????} ????????var day2 = day; ????????var days2 = new Date(year2, month2, 0); ????????days2 = days2.getDate(); ????????if (day2 > days2) { ????????????day2 = days2; ????????} ????????if (month2 < 10) { ????????????month2 = ‘0‘ + month2; ????????} ????????var t2 = year2 + ‘-‘ + month2 + ‘-‘ + day2; ????????return t2; ????}