addmonths/dist/addmonths.auto.js

Adds or sustract X months to any JavaScript Date.

(function () {
'use strict';

function addMonths(startdate, count) {
  var date = startdate && startdate.setUTCDate && new Date(+startdate);
  if (!(date instanceof Date)) {
    return startdate
  }
  count |= 0;
  if (!count || isNaN(date)) {
    return date
  }
  var offset = +date - date.setUTCHours(12, 0, 0, 0);
  var day = date.getUTCDate();
  date.setUTCMonth(date.getUTCMonth() + count, 2);
  var month = date.getUTCMonth();
  date.setUTCDate(day);
  if (date.getUTCMonth() !== month) {
    date.setUTCDate(0);
  }
  date.setMilliseconds(offset);
  return date
}

Object.defineProperty(Date.prototype, 'addMonths', {
  value: function (count) {
    return addMonths(this, count)
  },
  configurable: true,
  writable: true
});

}());