subtractZoned

Signature

subtractZoned(value: string, units: Partial<Record<DateTimeDurationUnit, number>>, optionsArg?: { disambiguation?: Disambiguation; offset?: Offset; overflow?: Overflow; }): string

import { subtractZoned } from "@northguild/gmt/zoned/calculate";

Subtract a temporal amount from a zoned ISO 8601 datetime string and return a zoned ISO 8601 string.

• Uses Temporal.ZonedDateTime.subtract to subtract duration.
• Validates duration units and values.
• Accepts a GMT calendar-annotated zoned string (as produced by convertZonedToCalendar, e.g. "5784-07-15T14:30:00-04:00[u-ca=hebrew][America/New_York]"), not just a bare ISO string — E7 (issue #152). Calendar-unit arithmetic (“subtract 1 month”) resolves against that calendar (a Hebrew leap month, an Ethiopic Pagumen, a Japanese era change) and the DST rules of the zone, in one operation. The calendar tag, the era, the wall time and the UTC offset are all re-derived from the result, never copied from the input. A bare ISO string is unaffected — always treated as, and always returns, "gregorian".
• disambiguation controls DST resolution ONLY when the arithmetic result lands on an ambiguous local time from a fall-back (DST-end) overlap: “compatible” (default), “earlier”, “later”, or “reject” (throws, resulting in “”). Has no effect when the result lands in a spring-forward (DST-start) gap — Temporal’s arithmetic always resolves gap landings unambiguously (by advancing past the gap) before disambiguation is ever evaluated.
• offset (“prefer” | “use” | “ignore” (default) | “reject”) is accepted for API consistency with sibling zoned-construction functions (see startOfZoned, endOfZoned, etc.) but has no effect here: the internal rebuild step reconstructs from a plain datetime string with no UTC offset embedded, so there is never a stored offset for offset to prefer/use/ignore/reject against. disambiguation is the only option that affects this function’s output.
• overflow (“constrain” (default) | “reject”) controls out-of-range results, e.g. subtracting 1 month from Mar 31: “constrain” clamps to Feb 29/28, “reject” throws (resulting in “”).
• Returns “” for invalid input.

Parameters

Parameter	Type	Description
value	string	ISO 8601 zoned datetime string, optionally calendar-annotated
units	Partial&lt;Record&lt;DateTimeDurationUnit, number&gt;&gt;	Partial<Record<DateTimeDurationUnit, number>> object specifying units to subtract

Options

options

Option	Type	Default
disambiguation?	Disambiguation	—
offset?	Offset	—
overflow?	Overflow	—

Returns

zoned ISO 8601 string on success, or “” on invalid input

Related types

• DurationUnit
• DateTimeDurationUnit
• Disambiguation
• Offset
• Overflow
• TimeDurationUnit

Examples

subtractZoned("2024-03-10T12:00:00-04:00[America/New_York]", { days: 5 }) // "2024-03-05T12:00:00-05:00[America/New_York]"
subtractZoned("invalid", { days: 5 }) // ""
subtractZoned("2024-11-04T01:30:00-05:00[America/New_York]", { days: 1 }, { disambiguation: "later" }) // "2024-11-03T01:30:00-05:00[America/New_York]" (fall-back overlap resolved; default "compatible" would return the -04:00 instant instead)
subtractZoned("2024-11-04T01:30:00-05:00[America/New_York]", { days: 1 }, { disambiguation: "reject" }) // "" (fall-back overlap rejected)
subtractZoned("2024-03-11T03:30:00-04:00[America/New_York]", { days: 1 }, { disambiguation: "reject" }) // "2024-03-10T03:30:00-04:00[America/New_York]" (spring-forward gap — disambiguation has no effect, arithmetic already advanced past it, so "reject" does not throw here)
subtractZoned("2024-03-31T12:00:00-04:00[America/New_York]", { months: 1 }, { overflow: "reject" }) // ""
subtractZoned("5784-07-15T14:30:00-04:00[u-ca=hebrew][America/New_York]", { months: 1 }) // "5784-06-15T14:30:00-05:00[u-ca=hebrew][America/New_York]" (Adar -> Adar I, EDT -> EST in one call)
subtractZoned("0001-05-01T12:00:00+09:00[u-ca=japanese;era=reiwa][Asia/Tokyo]", { days: 1 }) // "0031-04-30T12:00:00+09:00[u-ca=japanese;era=heisei][Asia/Tokyo]" (era re-derived, not copied)
subtractZoned("2024-03-10T14:30:00-04:00[America/New_York][u-ca=hebrew]", { days: 1 }) // "" (Temporal's segment ordering is not GMT's grammar)

Source

zoned/calculate/subtractZoned.ts