While most of the world uses the Gregorian calendar, there are several regional calendar eras used around the world. The calendar property's value is set at construction time, either through the ca key of the locale identifier or through the calendar option of the Intl.Locale() constructor. The latter takes priority if they are both present; and if neither is present, the property has value undefined.

For a list of supported calendar types, see Intl.Locale.prototype.getCalendars().

The set accessor of calendar is undefined. You cannot change this property directly.

Like other locale subtags, the calendar type can be added to the Intl.Locale object via the locale string, or a configuration object argument to the constructor.

In the Unicode locale string spec, calendar era types are locale key "extension subtags". These subtags add additional data about the locale, and are added to locale identifiers by using the -u extension. Thus, the calendar era type can be added to the initial locale identifier string that is passed into the Intl.Locale() constructor. To add the calendar type, first add the -u extension to the string. Next, add the -ca extension to indicate that you are adding a calendar type. Finally, add the calendar era type to the string.

const locale = new Intl.Locale("fr-FR-u-ca-buddhist");
console.log(locale.calendar); // Prints "buddhist"

The Intl.Locale() constructor has an optional configuration object argument, which can contain any of several extension types, including calendars. Set the calendar property of the configuration object to your desired calendar era, and then pass it into the constructor.

const locale = new Intl.Locale("fr-FR", { calendar: "buddhist" });
console.log(locale.calendar); // "buddhist"

• Intl.Locale
• Intl.Locale.prototype.getCalendars()
• Unicode Calendar Identifier in the Unicode locale data markup language spec