The era accessor property of Temporal.PlainDate instances returns a calendar-specific lowercase string representing the era of this date, or undefined if the calendar does not use eras (e.g., ISO 8601). era and eraYear together uniquely identify a year in a calendar, in the same way that year does. It is calendar-dependent. For Gregorian, it is either "ce" or "bce".
All specified calendars have eras fully defined by the spec.
The following calendars have a single era:
buddhist: "be"coptic: "am"ethioaa: "aa"hebrew: "am"indian: "shaka"persian: "ap"The following calendars have two eras. One is the epoch era, in which eraYear starts at 1 and is the same as year. The other is the inverse era, in which eraYear also starts at 1 and is equal to 1 - year (so eraYear: 1 corresponds to year 0, eraYear: 2 to year -1, etc.):
gregory: epoch era "ce", inverse era "bce"islamic-civil, islamic-tbla, islamic-umalqura: epoch era "ah", inverse era "bh"roc: epoch era "roc", inverse era "broc"The ethiopic calendar has an "am" era which is the epoch era. Years before 1 belong to the "aa" era, whose eraYear is equal to year - 5500 (so eraYear: -1000 corresponds to year -6500, eraYear: 1 corresponds to year -5499, up to eraYear: 5500 as year 0).
The japanese calendar adds an era for each new emperor, so the output year and era for a future date may not match the input year and era when your code runs on a future engine version, and we won't enumerate them here. Each era's year starts at 1. It is also the only calendar known to have eras starting in the middle of a year, which means that the same year may correspond to different (era, eraYear) pairs depending on the month and day.
Warning: As of October 2025, in the japanese calendar, dates prior to 1868-10-23 ISO (the start date of the year 1 Meiji) don't work as expected in browsers in two ways. First, CLDR had the wrong start date for the Meiji era, which causes calendar implementations to extend the Meiji era further to the past than it actually did. Second, the upcoming Intl era and monthCode Proposal specifies that dates prior to 1873-01-01 ISO should use Gregorian eras, but browsers have traditionally used approximations of prior Japanese eras instead. The japanese calendar was taken into use on January 1, 6 Meiji / 1873-01-01 ISO, so these problems only affect proleptic dates.
Other specified calendars: chinese, dangi, iso8601, don't use eras and return undefined.
The set accessor of era is undefined. You cannot change this property directly. Use the with() method to create a new Temporal.PlainDate object with the desired new value. When setting eras, the "ad" and "bc" aliases are also accepted for the "ce" and "bce" eras of the gregory or japanese calendars.
Note: This string is not intended for display to users. Use toLocaleString() with the appropriate options to get a localized string.
const date = Temporal.PlainDate.from("2021-07-01"); // ISO 8601 calendar
console.log(date.era); // undefined
const date2 = Temporal.PlainDate.from("2021-07-01[u-ca=gregory]");
console.log(date2.era); // ce
const date3 = Temporal.PlainDate.from("-002021-07-01[u-ca=gregory]");
console.log(date3.era); // bce
const date4 = Temporal.PlainDate.from("2021-07-01[u-ca=japanese]");
console.log(date4.era); // reiwaYou can only set era for calendars that support them. For example, the ISO 8601 calendar does not have eras. Note that you must provide era and eraYear together.
const date = Temporal.PlainDate.from("2021-07-01[u-ca=gregory]");
const newDate = date.with({ era: "bc", eraYear: 100 });
console.log(newDate.toString()); // -000099-07-01[u-ca=gregory]
const date2 = Temporal.PlainDate.from("2021-07-01[u-ca=japanese]");
const newDate2 = date2.with({ era: "meiji", eraYear: 1 });
console.log(newDate2.toString()); // 1868-07-01[u-ca=japanese]