65 lines
2.1 KiB
JavaScript
65 lines
2.1 KiB
JavaScript
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"use strict";
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exports.differenceInYears = differenceInYears;
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var _index = require("./_lib/normalizeDates.cjs");
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var _index2 = require("./compareAsc.cjs");
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var _index3 = require("./differenceInCalendarYears.cjs");
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/**
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* The {@link differenceInYears} function options.
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*/
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/**
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* @name differenceInYears
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* @category Year Helpers
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* @summary Get the number of full years between the given dates.
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*
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* @description
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* Get the number of full years between the given dates.
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*
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* @param laterDate - The later date
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* @param earlierDate - The earlier date
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* @param options - An object with options
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*
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* @returns The number of full years
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*
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* @example
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* // How many full years are between 31 December 2013 and 11 February 2015?
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* const result = differenceInYears(new Date(2015, 1, 11), new Date(2013, 11, 31))
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* //=> 1
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*/
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function differenceInYears(laterDate, earlierDate, options) {
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const [laterDate_, earlierDate_] = (0, _index.normalizeDates)(
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options?.in,
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laterDate,
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earlierDate,
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);
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// -1 if the left date is earlier than the right date
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// 2023-12-31 - 2024-01-01 = -1
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const sign = (0, _index2.compareAsc)(laterDate_, earlierDate_);
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// First calculate the difference in calendar years
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// 2024-01-01 - 2023-12-31 = 1 year
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const diff = Math.abs(
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(0, _index3.differenceInCalendarYears)(laterDate_, earlierDate_),
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);
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// Now we need to calculate if the difference is full. To do that we set
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// both dates to the same year and check if the both date's month and day
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// form a full year.
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laterDate_.setFullYear(1584);
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earlierDate_.setFullYear(1584);
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// For it to be true, when the later date is indeed later than the earlier date
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// (2026-02-01 - 2023-12-10 = 3 years), the difference is full if
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// the normalized later date is also later than the normalized earlier date.
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// In our example, 1584-02-01 is earlier than 1584-12-10, so the difference
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// is partial, hence we need to subtract 1 from the difference 3 - 1 = 2.
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const partial = (0, _index2.compareAsc)(laterDate_, earlierDate_) === -sign;
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const result = sign * (diff - +partial);
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// Prevent negative zero
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return result === 0 ? 0 : result;
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}
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