65 lines
1.5 KiB
JavaScript
65 lines
1.5 KiB
JavaScript
'use strict';
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var Chinese = require('./Chinese.cjs');
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/**
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* @copyright 2016 commenthol
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* @license MIT
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*/
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/**
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* @see http://law.e-gov.go.jp/htmldata/M19/M19CO051.html
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*/
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const UTC_DATES = [
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{
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date: new Date('1888-02-11T15:00:00.000Z'), // 1888-02-12T00:00:00+0900
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shift: 9 / 24
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} // +9:00:00h (135° East) Japanese standard meridian
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];
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/**
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* Note: I could not find details about the epoch(s) for the year zero of the
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* Japanese calendar dating before 1873. Therefore this calendar uses (wrongly)
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* the Chinese epoch.
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*
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* According to <https://en.wikipedia.org/wiki/History_of_Japan> the eras are:
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*
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* Yayoi 300 BC – 250 AD
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* Kofun 250 – 538
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* Asuka 538 – 710
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* Nara 710 – 794
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* Heian 794 – 1185
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* Kamakura 1185 – 1333
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* Kenmu Restoration 1333 – 1336
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* Muromachi 1336 – 1573
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* Azuchi–Momoyama 1568 – 1603
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* Edo 1603 – 1868
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* Meiji 1868 – 1912
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* Taishō 1912 – 1926
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* Shōwa 1926 – 1989
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* Heisei 1989 – present
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*
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* Unfortunately the linking from era to calendar era (especially to the Chinese
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* pre 1873 one) is unknown to me.
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*/
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class CalendarJapanese extends Chinese {
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/**
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* timeshift to UTC
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*
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* @param {CalendarGregorian} gcal - gregorian calendar date
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* @return {Number} timeshift in fraction of day
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*/
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timeshiftUTC (gcal) {
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const date = gcal.toDate();
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for (const i in UTC_DATES) {
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if (date >= UTC_DATES[i].date) {
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return UTC_DATES[i].shift
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}
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}
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return 4193 / 450 / 24 // +9:19:04h (139°46'E)
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}
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}
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module.exports = CalendarJapanese;
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