getWeekYear

Signature

getWeekYear(value: string): number

import { getWeekYear } from "@northguild/gmt/plain/calculate";

Return the ISO 8601 week-numbering year value belongs to.

• Distinct from value’s calendar year — late-December/early-January dates can belong to a different ISO week-year than their calendar year (e.g. 2024-12-30 is a Monday in ISO week 1 of 2025). Pair this with weekOfYearForDate when bucketing by week: a week number alone is ambiguous without the week-year it belongs to.
• Uses Temporal.PlainDate.yearOfWeek (ISO weeks: Monday-start, week 1 contains the year’s first Thursday).
• Returns null on invalid input.

Parameters

Parameter	Type	Description
value	string	ISO PlainDate string

Returns

ISO week-numbering year, or null on invalid input

Examples

getWeekYear("2024-06-15") // 2024
getWeekYear("2024-12-30") // 2025 (Monday of ISO week 1, 2025)
getWeekYear("2021-01-01") // 2020 (belongs to ISO week 53 of 2020)
getWeekYear("invalid") // null

Source

plain/calculate/getWeekYear.ts