intervalFromDurationDate

Signature

intervalFromDurationDate(value: string, duration: string, anchor: "start" | "end", options?: { overflow?: "reject" | "constrain" | undefined; }): { start: string; end: string; } | null

Construct a date interval from a single point plus an ISO 8601 duration, anchored at either end.

• anchor: "start" treats value as the interval start and adds duration to get the end.
• anchor: "end" treats value as the interval end and subtracts duration to get the start.
• Uses Temporal.PlainDate.prototype.add/.subtract semantics, so calendar units (years/months/weeks) resolve against value itself — no separate relativeTo is needed, unlike addDuration. Time units count as whole 24-hour days, as Temporal’s do.
• A negative duration (e.g. "-P1D") can invert the computed span; returns null when that happens, mirroring intervalIntersectionDate’s start > end rejection.
• Accepts a RFC 9557 calendar-annotated PlainDate string — E5 (issue #78). The computed endpoint is resolved in value’s own calendar (no relativeTo/pair-matching question, since there is only one calendar-tagged input) and both endpoints are re-formatted in that calendar, re-derived from the actual result rather than copied from value’s tag (a leap-month or era boundary can fall between them).
• Returns null on invalid input (unparseable value, invalid duration, or an anchor other than "start"/"end").

Parameters

Parameter	Type	Description
value	string	ISO PlainDate string, optionally calendar-annotated
duration	string	ISO 8601 duration string
anchor	"start" | "end"	“start” | “end” — which endpoint value represents

Options

options

How an out-of-range endpoint is handled

Option	Type	Default	Description
overflow?	"reject" | "constrain" (Overflow)	"constrain", Temporal’s default.	What to do when the computed endpoint is not a real date. "constrain" clamps it to the last valid day, so Jan 31 + 1 month is Feb 29 or 28; "reject" returns null.

Returns

{ start, end } with the constructed span, or null on invalid input

Members

Member	Type	Description
start	string	The date the interval begins on, as an ISO 8601 date (YYYY-MM-DD). It keeps a calendar annotation such as [u-ca=hebrew] when the inputs carry one.
end	string	The first date after the interval, in the same format as start. It is exclusive: the interval holds everything from start up to but not including this value. It can equal start, which makes the interval empty.

Related types

• Overflow

Examples

import { intervalFromDurationDate } from "@northguild/gmt/plain/interval";

intervalFromDurationDate("2024-01-01", "P1M", "start") // { start: "2024-01-01", end: "2024-02-01" }

valueduration

output

 

Source

plain/interval/intervalFromDurationDate.ts