43 lines
1.7 KiB
JavaScript
43 lines
1.7 KiB
JavaScript
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import toDate from '../toDate/index.js';
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import differenceInCalendarMonths from '../differenceInCalendarMonths/index.js';
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import compareAsc from '../compareAsc/index.js';
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/**
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* @name differenceInMonths
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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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* ### v2.0.0 breaking changes:
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*
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* - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
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*
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* @param {Date|Number} dateLeft - the later date
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* @param {Date|Number} dateRight - the earlier date
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* @returns {Number} the number of full months
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* @throws {TypeError} 2 arguments required
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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(new Date(2014, 8, 1), new Date(2014, 0, 31))
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* //=> 7
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*/
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export default function differenceInMonths(dirtyDateLeft, dirtyDateRight) {
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if (arguments.length < 2) {
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throw new TypeError('2 arguments required, but only ' + arguments.length + ' present');
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}
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var dateLeft = toDate(dirtyDateLeft);
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var dateRight = toDate(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); // 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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var result = sign * (difference - isLastMonthNotFull); // Prevent negative zero
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return result === 0 ? 0 : result;
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}
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