The calendarId accessor property of Temporal.PlainYearMonth instances returns a string representing the calendar used to interpret the internal ISO 8601 date.

See Intl.supportedValuesOf() for a list of commonly supported calendar types.

The set accessor of calendarId is undefined. You cannot change this property directly. There's no obvious way to create a new Temporal.PlainYearMonth object with a different calendar that represents the same year-month, so you need to convert it to a Temporal.PlainDate object first using toPlainDate(), change the calendar, and then convert it back.

Examples

Using calendarId

const ym = Temporal.PlainYearMonth.from("2021-07");
console.log(ym.calendarId); // "iso8601"; default

const ym2 = Temporal.PlainYearMonth.from("2021-07-01[u-ca=chinese]");
console.log(ym2.calendarId); // "chinese"

Changing calendarId

const ym = Temporal.PlainYearMonth.from("2021-07");
const newYM = ym
  .toPlainDate({ day: 1 })
  .withCalendar("chinese")
  .toPlainYearMonth();
console.log(newYM.year, newYM.monthCode); // 2021 "M05"

const newYM2 = ym
  .toPlainDate({ day: 31 })
  .withCalendar("chinese")
  .toPlainYearMonth();
console.log(newYM2.year, newYM2.monthCode); // 2021 "M06"

Specifications

Browser compatibility

See also

• Temporal.PlainYearMonth