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November 9, 2025 08:08
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大化の改新が二回起こる件について（蘇我入鹿は二度死ぬ）
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| const [localeYear, localeLongDate] = [{year: 'numeric'}, {dateStyle: 'long'}].map(o => | |
| d => d?.toLocaleString("ja-JP-u-ca-japanese", o)); | |
| const isoDate = d => d?.toISOString().slice(0, "yyyy-mm-dd".length); | |
| const d = new Date(643, 0, 1); // 643-01-01 | |
| const n = 365 * 4; // ~ 4 years | |
| let yPrev, dPrev; | |
| for (let i = 0; i < n; i++) { | |
| const y = localeYear(d); | |
| if (y !== yPrev) { | |
| const l = [dPrev, d].map(e => e && `${localeLongDate(e)} (${isoDate(e)})`); | |
| console.log(l.join(' -> ')); | |
| yPrev = y; | |
| } | |
| dPrev = new Date(d); // clone | |
| d.setDate(d.getDate() + 1); | |
| } |
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| $ node -v | |
| v25.1.0 | |
| $ node taika.js | |
| -> 大化-2年12月29日 (0642-12-31) | |
| 大化-2年12月31日 (0643-01-02) -> 大化元年1月1日 (0643-01-03) | |
| 大化元年12月31日 (0644-01-02) -> 大化0年1月1日 (0644-01-03) | |
| 大化0年12月31日 (0645-01-02) -> 大化元年1月1日 (0645-01-03) | |
| 大化元年12月31日 (0646-01-02) -> 大化2年1月1日 (0646-01-03) |
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