Temporal.PlainDate.prototype.weekOfYear

The weekOfYear accessor property of {{jsxref("Temporal.PlainDate")}} instances returns a positive integer representing the 1-based week index in the {{jsxref("Temporal/PlainDate/yearOfWeek", "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 {{jsxref("Temporal/PlainDate/yearOfWeek", "yearOfWeek")}} property, not the {{jsxref("Temporal/PlainDate/year", "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 {{jsxref("Temporal/PlainDate/add", "add()")}} or {{jsxref("Temporal/PlainDate/subtract", "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#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Temporal.PlainDate")}}
• {{jsxref("Temporal/PlainDate/with", "Temporal.PlainDate.prototype.with()")}}
• {{jsxref("Temporal/PlainDate/add", "Temporal.PlainDate.prototype.add()")}}
• {{jsxref("Temporal/PlainDate/subtract", "Temporal.PlainDate.prototype.subtract()")}}
• {{jsxref("Temporal/PlainDate/yearOfWeek", "Temporal.PlainDate.prototype.yearOfWeek")}}
• {{jsxref("Temporal/PlainDate/dayOfWeek", "Temporal.PlainDate.prototype.dayOfWeek")}}
• {{jsxref("Temporal/PlainDate/daysInWeek", "Temporal.PlainDate.prototype.daysInWeek")}}
• {{jsxref("Temporal/PlainDate/daysInYear", "Temporal.PlainDate.prototype.daysInYear")}}