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

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 day of the month:

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

	Desktop					Mobile						Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	Deno	Node.js
`monthsInYear`	No	No	No	No	No	No	No	No	No	No	No	1.40	No

Examples

Using monthsInYear

Changing to the second last month of the year

Specifications

Browser compatibility

See also