Temporal.PlainYearMonth.prototype.eraYear

The eraYear accessor property of Temporal.PlainYearMonth instances returns a non-negative integer representing the year of this year-month within the era, or undefined if the calendar does not use eras (e.g. ISO 8601). The year index usually starts from 1 (more common) or 0, and years in an era can decrease with time (e.g. Gregorian BCE). era and eraYear together uniquely identify a year in a calendar, in the same way that year does. It is calendar-dependent.

The set accessor of eraYear is undefined. You cannot change this property directly. Use the with() method to create a new Temporal.PlainYearMonth object with the desired new value.

For general information and more examples, see Temporal.PlainDate.prototype.eraYear.

const ym = Temporal.PlainYearMonth.from("2021-07"); // ISO 8601 calendar
console.log(ym.eraYear); // undefined

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

const ym3 = Temporal.PlainYearMonth.from("-002021-07-01[u-ca=gregory]");
console.log(ym3.eraYear); // 2022; 0000 is used for the year 1 BC

const ym4 = Temporal.PlainYearMonth.from("2021-07-01[u-ca=japanese]");
console.log(ym4.eraYear); // 3