39 lines
1.3 KiB
JavaScript
39 lines
1.3 KiB
JavaScript
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var parse = require('../parse/index.js')
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var differenceInCalendarMonths = require('../difference_in_calendar_months/index.js')
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var compareAsc = require('../compare_asc/index.js')
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/**
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* @category Month Helpers
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* @summary Get the number of full months between the given dates.
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*
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* @description
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* Get the number of full months between the given dates.
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*
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* @param {Date|String|Number} dateLeft - the later date
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* @param {Date|String|Number} dateRight - the earlier date
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* @returns {Number} the number of full months
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*
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* @example
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* // How many full months are between 31 January 2014 and 1 September 2014?
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* var result = differenceInMonths(
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* new Date(2014, 8, 1),
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* new Date(2014, 0, 31)
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* )
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* //=> 7
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*/
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function differenceInMonths (dirtyDateLeft, dirtyDateRight) {
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var dateLeft = parse(dirtyDateLeft)
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var dateRight = parse(dirtyDateRight)
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var sign = compareAsc(dateLeft, dateRight)
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var difference = Math.abs(differenceInCalendarMonths(dateLeft, dateRight))
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dateLeft.setMonth(dateLeft.getMonth() - sign * difference)
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// Math.abs(diff in full months - diff in calendar months) === 1 if last calendar month is not full
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// If so, result must be decreased by 1 in absolute value
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var isLastMonthNotFull = compareAsc(dateLeft, dateRight) === -sign
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return sign * (difference - isLastMonthNotFull)
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}
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module.exports = differenceInMonths
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