date-fns/src/eachYearOfInterval/index.js


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import toDate from '../toDate/index'
import requiredArgs from '../_lib/requiredArgs/index'

/**
 * @name eachYearOfInterval
 * @category Interval Helpers
 * @summary Return the array of yearly timestamps within the specified time interval.
 *
 * @description
 * Return the array of yearly timestamps within the specified time interval.
 *
 * @param {Interval} interval - the interval. See [Interval]{@link https://date-fns.org/docs/Interval}
 * @returns {Date[]} the array with starts of yearly timestamps from the month of the interval start to the month of the interval end
 * @throws {TypeError} 1 argument required
 * @throws {RangeError} The start of an interval cannot be after its end
 * @throws {RangeError} Date in interval cannot be `Invalid Date`
 *
 * @example
 * // Each year between 6 February 2014 and 10 August 2017:
 * var result = eachYearOfInterval({
 *   start: new Date(2014, 1, 6),
 *   end: new Date(2017, 7, 10)
 * })
 * //=> [
 * //   Wed Jan 01 2014 00:00:00,
 * //   Thu Jan 01 2015 00:00:00,
 * //   Fri Jan 01 2016 00:00:00,
 * //   Sun Jan 01 2017 00:00:00
 * // ]
 */
export default function eachYearOfInterval(dirtyInterval) {
  requiredArgs(1, arguments)

  var interval = dirtyInterval || {}
  var startDate = toDate(interval.start)
  var endDate = toDate(interval.end)

  var endTime = endDate.getTime()

  // Throw an exception if start date is after end date or if any date is `Invalid Date`
  if (!(startDate.getTime() <= endTime)) {
    throw new RangeError('Invalid interval')
  }

  var dates = []

  var currentDate = startDate
  currentDate.setHours(0, 0, 0, 0)
  currentDate.setMonth(0, 1)

  while (currentDate.getTime() <= endTime) {
    dates.push(toDate(currentDate))
    currentDate.setFullYear(currentDate.getFullYear() + 1)
  }

  return dates
}