index.js
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import startOfISOWeekYear from '../startOfISOWeekYear/index.js';
import addWeeks from '../addWeeks/index.js';
import requiredArgs from '../_lib/requiredArgs/index.js';
var MILLISECONDS_IN_WEEK = 604800000;
/**
* @name getISOWeeksInYear
* @category ISO Week-Numbering Year Helpers
* @summary Get the number of weeks in an ISO week-numbering year of the given date.
*
* @description
* Get the number of weeks in an ISO week-numbering year of the given date.
*
* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
*
* ### v2.0.0 breaking changes:
*
* - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
*
* @param {Date|Number} date - the given date
* @returns {Number} the number of ISO weeks in a year
* @throws {TypeError} 1 argument required
*
* @example
* // How many weeks are in ISO week-numbering year 2015?
* var result = getISOWeeksInYear(new Date(2015, 1, 11))
* //=> 53
*/
export default function getISOWeeksInYear(dirtyDate) {
requiredArgs(1, arguments);
var thisYear = startOfISOWeekYear(dirtyDate);
var nextYear = startOfISOWeekYear(addWeeks(thisYear, 60));
var diff = nextYear.valueOf() - thisYear.valueOf(); // Round the number of weeks to the nearest integer
// because the number of milliseconds in a week is not constant
// (e.g. it's different in the week of the daylight saving time clock shift)
return Math.round(diff / MILLISECONDS_IN_WEEK);
}