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- import toDate from "../toDate/index.js";
- import differenceInCalendarMonths from "../differenceInCalendarMonths/index.js";
- import compareAsc from "../compareAsc/index.js";
- import requiredArgs from "../_lib/requiredArgs/index.js";
- import isLastDayOfMonth from "../isLastDayOfMonth/index.js";
- /**
- * @name differenceInMonths
- * @category Month Helpers
- * @summary Get the number of full months between the given dates.
- *
- * @description
- * Get the number of full months between the given dates.
- *
- * ### 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} dateLeft - the later date
- * @param {Date|Number} dateRight - the earlier date
- * @returns {Number} the number of full months
- * @throws {TypeError} 2 arguments required
- *
- * @example
- * // How many full months are between 31 January 2014 and 1 September 2014?
- * var result = differenceInMonths(new Date(2014, 8, 1), new Date(2014, 0, 31))
- * //=> 7
- */
- export default function differenceInMonths(dirtyDateLeft, dirtyDateRight) {
- requiredArgs(2, arguments);
- var dateLeft = toDate(dirtyDateLeft);
- var dateRight = toDate(dirtyDateRight);
- var sign = compareAsc(dateLeft, dateRight);
- var difference = Math.abs(differenceInCalendarMonths(dateLeft, dateRight));
- var result; // Check for the difference of less than month
- if (difference < 1) {
- result = 0;
- } else {
- if (dateLeft.getMonth() === 1 && dateLeft.getDate() > 27) {
- // This will check if the date is end of Feb and assign a higher end of month date
- // to compare it with Jan
- dateLeft.setDate(30);
- }
- dateLeft.setMonth(dateLeft.getMonth() - sign * difference); // Math.abs(diff in full months - diff in calendar months) === 1 if last calendar month is not full
- // If so, result must be decreased by 1 in absolute value
- var isLastMonthNotFull = compareAsc(dateLeft, dateRight) === -sign; // Check for cases of one full calendar month
- if (isLastDayOfMonth(toDate(dirtyDateLeft)) && difference === 1 && compareAsc(dirtyDateLeft, dateRight) === 1) {
- isLastMonthNotFull = false;
- }
- result = sign * (difference - Number(isLastMonthNotFull));
- } // Prevent negative zero
- return result === 0 ? 0 : result;
- }
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