The month accessor property of Temporal.PlainDate instances returns a positive integer representing the 1-based month index in the year of this date. The first month of this year is 1, and the last month is the monthsInYear. It is calendar-dependent.

The toJSON() method of Temporal.PlainYearMonth instances returns a string representing this year-month in the same RFC 9557 format as calling toString(). It is intended to be implicitly called by JSON.stringify().

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The add() method of Temporal.Instant instances returns a new Temporal.Instant object representing this instant moved forward by a given duration (in a form convertible by Temporal.Duration.from()).

The withCalendar() method of Temporal.PlainDateTime instances returns a new Temporal.PlainDateTime object representing this date-time interpreted in the new calendar system. Because all Temporal objects are designed to be immutable, this method essentially functions as the setter for the date-time's calendarId property.

The daysInWeek accessor property of Temporal.PlainDateTime instances returns a positive integer representing the number of days in the week of this date. It is calendar-dependent.

The withCalendar() method of Temporal.ZonedDateTime instances returns a new Temporal.ZonedDateTime object representing this date-time interpreted in the new calendar system. Because all Temporal objects are designed to be immutable, this method essentially functions as the setter for the date-time's calendarId property.