1 月份加减方法（公共方法）
//月份加减
function addMonths(yearMonthDay,monthNum){var arr=yearMonthDay.split('-');//2020-08-19或2020-08var year=parseInt(arr[0]);var month=parseInt(arr[1]);month=month+monthNum;if(month>12){//月份加var yearNum=parseInt((month-1)/12);month=month%12==0?12:month%12;year+=yearNum;}else if(month<=0){//月份减month=Math.abs(month);var yearNum=parseInt((month+12)/12);year-=yearNum;}month=month<10?"0"+month:month;return year+"-"+month;
}
2 方法调试
var yearMonth1=addMonths("2020-08",-20);//2018-12
var yearMonth2=addMonths("2020-08",-8);//2019-12
var yearMonth3=addMonths("2020-08",-19);//2019-01
var yearMonth4=addMonths("2020-08",5);//2021-01
var yearMonth5=addMonths("2020-08",16);//2021-12
var yearMonth6=addMonths("2020-08",17);//2022-01