Temporal.PlainDate.prototype.weekOfYear

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 weekOfYear accessor property of Temporal.PlainDate instances returns a positive integer representing the 1-based week index in the yearOfWeek of this date, or undefined if the calendar does not have a well-defined week system. The first week of the year is 1. It is calendar-dependent.

Note that for ISO 8601, the first and last few days of the year may be attributed to the last week of the previous year or the first week of the next year. Namely, if a week crosses two years, then it belongs to the year that has the majority of its days. To get the year that the weekOfYear belongs to, use the yearOfWeek property, not the year property.

The set accessor of weekOfYear is undefined. You cannot change this property directly. To create a new Temporal.PlainDate object with the desired new weekOfYear value, use the add() or subtract() method with the appropriate number of weeks.

Examples

Using weekOfYear

const date = Temporal.PlainDate.from("2021-07-01");
console.log(date.weekOfYear); // 26

// If 01-01 is a Friday/Saturday/Sunday, it belongs to the last week of the previous year
const date2 = Temporal.PlainDate.from("2021-01-01");
console.log(date2.dayOfWeek); // 5
console.log(date2.weekOfYear); // 53; 2020 has 53 weeks
console.log(date2.yearOfWeek); // 2020

// Otherwise, it belongs to the first week of the year
const date3 = Temporal.PlainDate.from("2020-01-01");
console.log(date3.dayOfWeek); // 3
console.log(date3.weekOfYear); // 1
console.log(date3.yearOfWeek); // 2020

// Similarly, if 12-31 is a Monday/Tuesday/Wednesday, it belongs to the first week of the next year
const date4 = Temporal.PlainDate.from("2019-12-31");
console.log(date4.dayOfWeek); // 2
console.log(date4.weekOfYear); // 1
console.log(date4.yearOfWeek); // 2020

Changing weekOfYear

PlainDate does not support changing weekOfYear directly. To change the week, you need to first figure out the difference in weeks to your desired week, then use add or subtract to adjust the date accordingly. For example, to change to the previous week:

const date = Temporal.PlainDate.from("2021-07-01");
const previousWeek = date.subtract({ weeks: 1 });
console.log(previousWeek.toString()); // 2021-06-24

Specifications

Specification
Temporal # sec-get-temporal.plaindate.prototype.weekofyear

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
`weekOfYear`	No	No	139	No	No	No	139	No	No	No	No	1.40	No

Examples

Using weekOfYear

Changing weekOfYear

Specifications

Browser compatibility

See also