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@leshakoss @kossnocorp @dandv

Unicode Tokens

Starting with v2, format and parse use Unicode tokens.

The tokens are different from Moment.js and other libraries that opted to use custom formatting rules. While usage of a standard ensures compatibility and the future of the library, it causes confusion that this document intends to resolve.

Popular mistakes

There are 4 tokens that cause most of the confusion:

  • D and DD that represent the day of a year (1, 2, ..., 365, 366) are often confused with d and dd that represent the day of a month (1, 2, ..., 31).

  • YY and YYYY that represent the local week-numbering year (44, 01, 00, 17) are often confused with yy and yyyy that represent the calendar year.

// ❌ Wrong!
format(new Date(), 'YYYY-MM-DD')
//=> 2018-10-283

// ✅ Correct
format(new Date(), 'yyyy-MM-dd')
//=> 2018-10-10

// ❌ Wrong!
parse('11.02.87', 'D.MM.YY', new Date()).toString()
//=> 'Sat Jan 11 1986 00:00:00 GMT+0200 (EET)'

// ✅ Correct
parse('11.02.87', 'd.MM.yy', new Date()).toString()
//=> 'Wed Feb 11 1987 00:00:00 GMT+0200 (EET)'

To help with the issue, format and parse functions won't accept these tokens without useAdditionalDayOfYearTokens option for D and DD and useAdditionalWeekYearTokens options for YY and YYYY:

format(new Date(), 'D', { useAdditionalDayOfYearTokens: true })
//=> '283'

parse('365+1987', 'DD+YYYY', new Date(), {
  useAdditionalDayOfYearTokens: true,
  useAdditionalWeekYearTokens: true
}).toString()
//=> 'Wed Dec 31 1986 00:00:00 GMT+0200 (EET)'