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 proposal # sec-get-temporal.plaindate.prototype.weekofyear |