78 lines
3.0 KiB
JavaScript
78 lines
3.0 KiB
JavaScript
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"use strict";
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Object.defineProperty(exports, "__esModule", {
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value: true
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});
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exports.default = addMonths;
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var _index = _interopRequireDefault(require("../_lib/toInteger/index.js"));
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var _index2 = _interopRequireDefault(require("../toDate/index.js"));
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var _index3 = _interopRequireDefault(require("../_lib/requiredArgs/index.js"));
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function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
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/**
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* @name addMonths
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* @category Month Helpers
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* @summary Add the specified number of months to the given date.
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*
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* @description
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* Add the specified number of months to the given date.
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*
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* @param {Date|Number} date - the date to be changed
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* @param {Number} amount - the amount of months to be added. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
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* @returns {Date} the new date with the months added
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* @throws {TypeError} 2 arguments required
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*
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* @example
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* // Add 5 months to 1 September 2014:
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* const result = addMonths(new Date(2014, 8, 1), 5)
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* //=> Sun Feb 01 2015 00:00:00
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*/
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function addMonths(dirtyDate, dirtyAmount) {
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(0, _index3.default)(2, arguments);
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var date = (0, _index2.default)(dirtyDate);
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var amount = (0, _index.default)(dirtyAmount);
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if (isNaN(amount)) {
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return new Date(NaN);
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}
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if (!amount) {
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// If 0 months, no-op to avoid changing times in the hour before end of DST
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return date;
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}
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var dayOfMonth = date.getDate(); // The JS Date object supports date math by accepting out-of-bounds values for
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// month, day, etc. For example, new Date(2020, 0, 0) returns 31 Dec 2019 and
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// new Date(2020, 13, 1) returns 1 Feb 2021. This is *almost* the behavior we
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// want except that dates will wrap around the end of a month, meaning that
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// new Date(2020, 13, 31) will return 3 Mar 2021 not 28 Feb 2021 as desired. So
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// we'll default to the end of the desired month by adding 1 to the desired
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// month and using a date of 0 to back up one day to the end of the desired
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// month.
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var endOfDesiredMonth = new Date(date.getTime());
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endOfDesiredMonth.setMonth(date.getMonth() + amount + 1, 0);
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var daysInMonth = endOfDesiredMonth.getDate();
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if (dayOfMonth >= daysInMonth) {
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// If we're already at the end of the month, then this is the correct date
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// and we're done.
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return endOfDesiredMonth;
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} else {
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// Otherwise, we now know that setting the original day-of-month value won't
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// cause an overflow, so set the desired day-of-month. Note that we can't
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// just set the date of `endOfDesiredMonth` because that object may have had
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// its time changed in the unusual case where where a DST transition was on
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// the last day of the month and its local time was in the hour skipped or
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// repeated next to a DST transition. So we use `date` instead which is
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// guaranteed to still have the original time.
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date.setFullYear(endOfDesiredMonth.getFullYear(), endOfDesiredMonth.getMonth(), dayOfMonth);
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return date;
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}
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}
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module.exports = exports.default;
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