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

js
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:

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

Specifications

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

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
weekOfYear
Experimental

Legend

Tip: you can click/tap on a cell for more information.

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

See also