42 lines
1.6 KiB
JavaScript
42 lines
1.6 KiB
JavaScript
var parse = require('../parse/index.js')
|
|
var differenceInCalendarISOYears = require('../difference_in_calendar_iso_years/index.js')
|
|
var compareAsc = require('../compare_asc/index.js')
|
|
var subISOYears = require('../sub_iso_years/index.js')
|
|
|
|
/**
|
|
* @category ISO Week-Numbering Year Helpers
|
|
* @summary Get the number of full ISO week-numbering years between the given dates.
|
|
*
|
|
* @description
|
|
* Get the number of full ISO week-numbering years between the given dates.
|
|
*
|
|
* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
|
|
*
|
|
* @param {Date|String|Number} dateLeft - the later date
|
|
* @param {Date|String|Number} dateRight - the earlier date
|
|
* @returns {Number} the number of full ISO week-numbering years
|
|
*
|
|
* @example
|
|
* // How many full ISO week-numbering years are between 1 January 2010 and 1 January 2012?
|
|
* var result = differenceInISOYears(
|
|
* new Date(2012, 0, 1),
|
|
* new Date(2010, 0, 1)
|
|
* )
|
|
* //=> 1
|
|
*/
|
|
function differenceInISOYears (dirtyDateLeft, dirtyDateRight) {
|
|
var dateLeft = parse(dirtyDateLeft)
|
|
var dateRight = parse(dirtyDateRight)
|
|
|
|
var sign = compareAsc(dateLeft, dateRight)
|
|
var difference = Math.abs(differenceInCalendarISOYears(dateLeft, dateRight))
|
|
dateLeft = subISOYears(dateLeft, sign * difference)
|
|
|
|
// Math.abs(diff in full ISO years - diff in calendar ISO years) === 1
|
|
// if last calendar ISO year is not full
|
|
// If so, result must be decreased by 1 in absolute value
|
|
var isLastISOYearNotFull = compareAsc(dateLeft, dateRight) === -sign
|
|
return sign * (difference - isLastISOYearNotFull)
|
|
}
|
|
|
|
module.exports = differenceInISOYears
|