date-fns/add_months/index.js

Modern JavaScript date utility library

var parse = require('../parse/index.js')
var getDaysInMonth = require('../get_days_in_month/index.js')

/**
 * @category Month Helpers
 * @summary Add the specified number of months to the given date.
 *
 * @description
 * Add the specified number of months to the given date.
 *
 * @param {Date|String|Number} date - the date to be changed
 * @param {Number} amount - the amount of months to be added
 * @returns {Date} the new date with the months added
 *
 * @example
 * // Add 5 months to 1 September 2014:
 * var result = addMonths(new Date(2014, 8, 1), 5)
 * //=> Sun Feb 01 2015 00:00:00
 */
function addMonths (dirtyDate, amount) {
  var date = parse(dirtyDate)
  var desiredMonth = date.getMonth() + amount
  var daysInMonth = getDaysInMonth(new Date(date.getFullYear(), desiredMonth, 1))
  // Set the last day of the new month
  // if the original date was the last day of the longer month
  date.setMonth(desiredMonth, Math.min(daysInMonth, date.getDate()))
  return date
}

module.exports = addMonths