tiny-ja-date

Tiny TypeScript date utilities for Japanese UI.

• 日本語の日付表示
• 日本語の相対日付表示
• 土日判定
• 次の営業日計算

Install

npm install tiny-ja-date

Usage

import {
  formatJaDate,
  formatRelativeJaDate,
  isWeekendJP,
  nextBusinessDay,
} from "tiny-ja-date"

formatJaDate(new Date(2026, 4, 12))
// "2026年5月12日（火）"

formatRelativeJaDate(new Date(2026, 4, 15), new Date(2026, 4, 12))
// "3日後"

isWeekendJP(new Date(2026, 4, 16))
// true

nextBusinessDay(new Date(2026, 4, 15))
// Date for 2026-05-18

API

formatJaDate(date: Date | string | number): string

Formats a date as a Japanese date label.

formatJaDate(new Date(2026, 4, 12))
// "2026年5月12日（火）"

formatRelativeJaDate(date: Date | string | number, baseDate?: Date | string | number): string

Formats a date relative to a base date.

formatRelativeJaDate(new Date(2026, 4, 12), new Date(2026, 4, 12))
// "今日"

formatRelativeJaDate(new Date(2026, 4, 11), new Date(2026, 4, 12))
// "昨日"

formatRelativeJaDate(new Date(2026, 4, 13), new Date(2026, 4, 12))
// "明日"

formatRelativeJaDate(new Date(2026, 4, 9), new Date(2026, 4, 12))
// "3日前"

formatRelativeJaDate(new Date(2026, 4, 15), new Date(2026, 4, 12))
// "3日後"

isWeekendJP(date: Date | string | number): boolean

Checks whether the date is Saturday or Sunday.

isWeekendJP(new Date(2026, 4, 16))
// true

nextBusinessDay(date: Date | string | number): Date

Returns the next business day.

The input date itself is not included.

nextBusinessDay(new Date(2026, 4, 15))
// Date for 2026-05-18

Note

Business day calculation excludes weekends only.

Japanese holidays are intentionally out of scope for v0.1.

Design policy

tiny-ja-date is intentionally small.

It does not:

• include Japanese holiday data
• convert time zones
• format wareki
• generate calendars
• replace date-fns or dayjs

Live Demo

• Demo → https://fusaihanabi.github.io/tiny-ja-date
• npm → https://www.npmjs.com/package/tiny-ja-date
• GitHub → https://github.com/fusaihanabi/tiny-ja-date
• Official → https://dl.fusai-hanabi.com

License

MIT