我写了另一种解决方案，对我来说很好。当您希望计算合同的结束时，它很有用。例如，start=2016-01-15, months=6, end=2016-7-14(即最后一天-1):

<script>
function daysInMonth(year, month)
{
    return new Date(year, month + 1, 0).getDate();
}

function addMonths(date, months)
{
    var target_month = date.getMonth() + months;
    var year = date.getFullYear() + parseInt(target_month / 12);
    var month = target_month % 12;
    var day = date.getDate();
    var last_day = daysInMonth(year, month);
    if (day > last_day)
    {
        day = last_day;
    }
    var new_date = new Date(year, month, day);
    return new_date;
}

var endDate = addMonths(startDate, months);
</script>

例子:

addMonths(new Date("2016-01-01"), 1); // 2016-01-31
addMonths(new Date("2016-01-01"), 2); // 2016-02-29 (2016 is a leap year)
addMonths(new Date("2016-01-01"), 13); // 2017-01-31
addMonths(new Date("2016-01-01"), 14); // 2017-02-28

var a=new Date();
a.setDate(a.getDate()+5);

如上所述的方法，您可以添加月到日期功能。

考虑到这些答案中没有一个会在月份变化时解释当年的情况，你可以在下面找到我做的一个答案，它应该可以处理这个问题:

方法:

Date.prototype.addMonths = function (m) {
    var d = new Date(this);
    var years = Math.floor(m / 12);
    var months = m - (years * 12);
    if (years) d.setFullYear(d.getFullYear() + years);
    if (months) d.setMonth(d.getMonth() + months);
    return d;
}

用法:

return new Date().addMonths(2);

容易的,简单的

function addMonths(date, months) {date.setMonth(date.getMonth() + months); return date;};

使用它作为

 alert(new Date().toLocaleString()); //will say today
 alert(addMonths(new Date(),12).toLocaleString()); //will say next year, same day and month

从上面的答案，唯一一个处理边缘情况(bmpasini的datejs库)有一个问题:

var date = new Date("03/31/2015");
var newDate = date.addMonths(1);
console.log(newDate);
// VM223:4 Thu Apr 30 2015 00:00:00 GMT+0200 (CEST)

好吧,但是:

newDate.toISOString()
//"2015-04-29T22:00:00.000Z"

更糟糕的是:

var date = new Date("01/01/2015");
var newDate = date.addMonths(3);
console.log(newDate);
//VM208:4 Wed Apr 01 2015 00:00:00 GMT+0200 (CEST)
newDate.toISOString()
//"2015-03-31T22:00:00.000Z"

这是由于时间没有设置，因此返回到00:00:00，然后可能由于时区或节省时间的更改或其他原因而故障到前一天…

下面是我提出的解决方案，它不存在这个问题，而且我认为它更优雅，因为它不依赖于硬编码的值。

/**
* @param isoDate {string} in ISO 8601 format e.g. 2015-12-31
* @param numberMonths {number} e.g. 1, 2, 3...
* @returns {string} in ISO 8601 format e.g. 2015-12-31
*/
function addMonths (isoDate, numberMonths) {
    var dateObject = new Date(isoDate),
        day = dateObject.getDate(); // returns day of the month number

    // avoid date calculation errors
    dateObject.setHours(20);

    // add months and set date to last day of the correct month
    dateObject.setMonth(dateObject.getMonth() + numberMonths + 1, 0);

    // set day number to min of either the original one or last day of month
    dateObject.setDate(Math.min(day, dateObject.getDate()));

    return dateObject.toISOString().split('T')[0];
};

单元测试成功，使用:

function assertEqual(a,b) {
    return a === b;
}
console.log(
    assertEqual(addMonths('2015-01-01', 1), '2015-02-01'),
    assertEqual(addMonths('2015-01-01', 2), '2015-03-01'),
    assertEqual(addMonths('2015-01-01', 3), '2015-04-01'),
    assertEqual(addMonths('2015-01-01', 4), '2015-05-01'),
    assertEqual(addMonths('2015-01-15', 1), '2015-02-15'),
    assertEqual(addMonths('2015-01-31', 1), '2015-02-28'),
    assertEqual(addMonths('2016-01-31', 1), '2016-02-29'),
    assertEqual(addMonths('2015-01-01', 11), '2015-12-01'),
    assertEqual(addMonths('2015-01-01', 12), '2016-01-01'),
    assertEqual(addMonths('2015-01-01', 24), '2017-01-01'),
    assertEqual(addMonths('2015-02-28', 12), '2016-02-28'),
    assertEqual(addMonths('2015-03-01', 12), '2016-03-01'),
    assertEqual(addMonths('2016-02-29', 12), '2017-02-28')
);

最简单的解决方法是:

const todayDate = Date.now();
return new Date(todayDate + 1000 * 60 * 60 * 24 * 30* X); 

其中X是我们想要增加的月份数。