Temporal.PlainDate.prototype.monthsInYear

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The monthsInYear accessor property of Temporal.PlainDate instances returns a positive integer representing the number of months in the year of this date. It is calendar-dependent.

For the ISO 8601 calendar, this is always 12, but in other calendar systems it may differ. For example, in calendars using leap months, leap years will have one more month than common years.

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

Examples

Using monthsInYear

js
const date = Temporal.PlainDate.from("2021-07-01");
console.log(date.monthsInYear); // 12

const date2 = Temporal.PlainDate.from("2021-07-01[u-ca=chinese]");
console.log(date2.monthsInYear); // 12

const date3 = Temporal.PlainDate.from("2023-07-01[u-ca=chinese]");
console.log(date3.monthsInYear); // 13; 2023 is a Chinese leap year

Changing to the second last month of the year

You can use monthsInYear to change to the second last month of the year:

js
const date = Temporal.PlainDate.from("2021-07-01");
const secondLastMonth = date.with({ month: date.monthsInYear - 1 });
console.log(secondLastMonth.toString()); // 2021-11-01

Specifications

Specification
Temporal proposal
# sec-get-temporal.plaindate.prototype.monthsinyear

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
monthsInYear
Experimental

Legend

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No support
No support
Experimental. Expect behavior to change in the future.
See implementation notes.
User must explicitly enable this feature.

See also