isRelativeDay

Signature

isRelativeDay(value: string, offsetDays: number): boolean

import { isRelativeDay } from "@northguild/gmt/plain/compare";

Return true when value falls offsetDays days from today, per the

• system clock and system timeZone.
• Subsumes isToday/isYesterday/isTomorrow: offsetDays: 0 is “today”, -1 is “yesterday”, 1 is “tomorrow”, and any other integer offset works the same way.
• Compares against getToday(), so this depends on the system clock and system timeZone. The same call returns different answers on hosts in different timeZones at the same instant — a caller needing determinism (server-side rendering, tests, scheduled jobs) should use isZonedRelativeDay with an explicit timeZone, or compare against an explicit reference with areDatesEqualBy.
• offsetDays must be an integer; non-integer or non-finite values return false.
• Returns false if value is invalid or the system timeZone is unavailable. Mapping from date-fns (Decision 5, context/roadmap/issues/J.md):
• isToday(value) → isRelativeDay(value, 0)
• isYesterday(value) → isRelativeDay(value, -1)
• isTomorrow(value) → isRelativeDay(value, 1)

Parameters

Parameter	Type	Description
value	string	ISO PlainDate string
offsetDays	number	integer number of days from today (0 = today, -1 = yesterday, 1 = tomorrow)

Returns

true if value is exactly offsetDays days from today, false on invalid input

Examples

isRelativeDay("2024-03-15", 0) // true, if today is 2024-03-15
isRelativeDay("2024-03-14", -1) // true, if today is 2024-03-15
isRelativeDay("2024-03-22", 7) // true, if today is 2024-03-15
isRelativeDay("2024-03-15", 1.5) // false (offsetDays must be an integer)
isRelativeDay("invalid", 0) // false

Source

plain/compare/isRelativeDay.ts