datefns 格式未完全格式化

Question

I am using react and datefns.

I have the following code

import { enUS, ja } from 'date-fns/locale';
import { format, isValid, parseISO } from 'date-fns';


export const getDateLocal = (locale?: string) => {
  switch (locale) {
    case 'ja':
      return ja;
    case 'en':
    default:
      return enUS;
  }
};

export const localizedDateFormatter = (
  date: Date | number | string,
  dateFormat = 'MMM dd',
  locale = 'en'
): string => {
  const dateIsIso = typeof date === 'string' ? isValid(parseISO(date)) : false;
  if (!date || (!dateIsIso && !isValid(date))) {
    return '-';
  }

  return format(new Date(date), dateFormat, { locale: getDateLocal(locale) });
};

I call this function like this

localizedDateFormatter(hoverFrom, 'MMM dd, yyyy', i18n.language) // can be ja or en

The problem is, the date is not converted like I would like.

ja: 12月 15, 2020 

en: Dec 15, 2020

While it should be

ja: 2020年1月13日 (or at least 1月13日, 2020年)

en: Dec 15, 2020

Why so?

Answer 1

DISCLAIMER

I have not clue about japanese, so I can give an answer just looking at the source code, but maybe some japanese speaker could give a more precise answer.

---

You can check the locale source code here https://github.com/date-fns/date-fns/tree/master/src/locale/ja/_lib , but here are some insights I managed to discover.

DAY

The日character follows the day on its ordinal form (also it seems to be the name for Sunday). Look at here . So you need do (ordinal day of month).

MONTH

The月character follows the month number when displaying the month's name (abbreviated or full). So if you use M to display the month it won't show. You need MMM or MMMM . Compare JA with EN-US .

YEAR

The年character follows the year only if the date is in long format. This character is nowhere in this file, but it is here on the long and full date format ( PPP and PPPP ).

---

The japanese format that you are looking for is PPP which shows dates like this:

• EN : February 15th, 2020
• JA : 2020年2月15日

The closest you can get to the format you where looking for is MMM do, yyyy :

• EN : Feb 15th, 2020
• JA : 2月 15日, 2020