index.js
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var startOfWeek = require('../start_of_week/index.js')
var MILLISECONDS_IN_MINUTE = 60000
var MILLISECONDS_IN_WEEK = 604800000
/**
* @category Week Helpers
* @summary Get the number of calendar weeks between the given dates.
*
* @description
* Get the number of calendar weeks between the given dates.
*
* @param {Date|String|Number} dateLeft - the later date
* @param {Date|String|Number} dateRight - the earlier date
* @param {Object} [options] - the object with options
* @param {Number} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
* @returns {Number} the number of calendar weeks
*
* @example
* // How many calendar weeks are between 5 July 2014 and 20 July 2014?
* var result = differenceInCalendarWeeks(
* new Date(2014, 6, 20),
* new Date(2014, 6, 5)
* )
* //=> 3
*
* @example
* // If the week starts on Monday,
* // how many calendar weeks are between 5 July 2014 and 20 July 2014?
* var result = differenceInCalendarWeeks(
* new Date(2014, 6, 20),
* new Date(2014, 6, 5),
* {weekStartsOn: 1}
* )
* //=> 2
*/
function differenceInCalendarWeeks (dirtyDateLeft, dirtyDateRight, dirtyOptions) {
var startOfWeekLeft = startOfWeek(dirtyDateLeft, dirtyOptions)
var startOfWeekRight = startOfWeek(dirtyDateRight, dirtyOptions)
var timestampLeft = startOfWeekLeft.getTime() -
startOfWeekLeft.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
var timestampRight = startOfWeekRight.getTime() -
startOfWeekRight.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
// Round the number of days 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((timestampLeft - timestampRight) / MILLISECONDS_IN_WEEK)
}
module.exports = differenceInCalendarWeeks