获取指定日期加月份

function AddMouth(date, num){
var mouthnum = parseInt(num);
var year = parseInt(date.substring(0, 4));
var mouth = parseInt(date.substring(5, 7));
var day = parseInt(date.substring(8, 10));
if (mouth + mouthnum > 12){
var newyear = year + 1;
var newmouth = mouth + mouthnum - 12;
while(newmouth>12){
newyear=newyear+1;
newmouth=newmouth-12;
}
var newday = day;
}else{
var newyear = year
var newmouth = mouth + mouthnum;
var newday = day;
}
var newdate = newyear + “-” + newmouth + “-” + newday;
return newdate;
}