Source: add/index.ts

import addDays from '../addDays/index'
import addMonths from '../addMonths/index'
import toDate from '../toDate/index'
import requiredArgs from '../_lib/requiredArgs/index'
import toInteger from '../_lib/toInteger/index'
import { Duration } from '../types'

/**
 * @name add
 * @category Common Helpers
 * @summary Add the specified years, months, weeks, days, hours, minutes and seconds to the given date.
 *
 * @description
 * Add the specified years, months, weeks, days, hours, minutes and seconds to the given date.
 *
 * @param {Date|Number} date - the date to be changed
 * @param {Duration} duration - the object with years, months, weeks, days, hours, minutes and seconds to be added. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
 *
 * | Key            | Description                        |
 * |----------------|------------------------------------|
 * | years          | Amount of years to be added        |
 * | months         | Amount of months to be added       |
 * | weeks          | Amount of weeks to be added       |
 * | days           | Amount of days to be added         |
 * | hours          | Amount of hours to be added        |
 * | minutes        | Amount of minutes to be added      |
 * | seconds        | Amount of seconds to be added      |
 *
 * All values default to 0
 *
 * @returns {Date} the new date with the seconds added
 * @throws {TypeError} 2 arguments required
 *
 * @example
 * // Add the following duration to 1 September 2014, 10:19:50
 * var result = add(new Date(2014, 8, 1, 10, 19, 50), {
 *   years: 2,
 *   months: 9,
 *   weeks: 1,
 *   days: 7,
 *   hours: 5,
 *   minutes: 9,
 *   seconds: 30,
 * })
 * //=> Thu Jun 15 2017 15:29:20
 */
export default function add(
  dirtyDate: Date | number,
  duration: Duration
): Date {
  requiredArgs(2, arguments)

  if (!duration || typeof duration !== 'object') return new Date(NaN)

  const years = 'years' in duration ? toInteger(duration.years) : 0
  const months = 'months' in duration ? toInteger(duration.months) : 0
  const weeks = 'weeks' in duration ? toInteger(duration.weeks) : 0
  const days = 'days' in duration ? toInteger(duration.days) : 0
  const hours = 'hours' in duration ? toInteger(duration.hours) : 0
  const minutes = 'minutes' in duration ? toInteger(duration.minutes) : 0
  const seconds = 'seconds' in duration ? toInteger(duration.seconds) : 0

  // Add years and months
  const date = toDate(dirtyDate)
  const dateWithMonths =
    months || years ? addMonths(date, months + years * 12) : date

  // Add weeks and days
  const dateWithDays =
    days || weeks ? addDays(dateWithMonths, days + weeks * 7) : dateWithMonths

  // Add days, hours, minutes and seconds
  const minutesToAdd = minutes + hours * 60
  const secondsToAdd = seconds + minutesToAdd * 60
  const msToAdd = secondsToAdd * 1000
  const finalDate = new Date(dateWithDays.getTime() + msToAdd)

  return finalDate
}