intervalOverlappingDaysUnix

Signature

intervalOverlappingDaysUnix(aStart: string | number, aEnd: string | number, bStart: string | number, bEnd: string | number, options?: { epochUnit?: "seconds" | "milliseconds"; timeZone?: string; }): number

import { intervalOverlappingDaysUnix } from "@northguild/gmt/unix/interval";

Return how many distinct calendar dates two Unix epoch intervals share, in a given

• time zone.
• Counts the number of local dates touched by the closed intersection [max(aStart, bStart), min(aEnd, bEnd)] — inclusive of both endpoints.
• Uses the system timeZone by default (consistent with addUnix and intervalCountUnix), so day counts are host-dependent unless timeZone is given.
• Adjacent intervals (e.g. aEnd === bStart) share one date and count as 1.
• Returns 0 when the intervals do not overlap at all (a well-defined answer, not invalid input).
• Returns null if either interval is invalid (start > end).
• Returns null on invalid input (non-finite/non-integer epoch values, invalid timeZone).
• Diverges from date-fns’s getOverlappingDaysInIntervals, which rounds up elapsed 24-hour periods instead of counting calendar dates. To reproduce date-fns’s number, compose intervalIntersectionUnix with intervalCountUnix: const span = intervalIntersectionUnix(aStart, aEnd, bStart, bEnd); span ? intervalCountUnix(span.start, span.end, "day") : 0;

Parameters

Parameter	Type	Description
aStart	string | number	Unix epoch value (seconds or milliseconds) — first interval start
aEnd	string | number	Unix epoch value (seconds or milliseconds) — first interval end
bStart	string | number	Unix epoch value (seconds or milliseconds) — second interval start
bEnd	string | number	Unix epoch value (seconds or milliseconds) — second interval end

Options

options

Option	Type	Default
epochUnit?	"seconds" | "milliseconds"	—
timeZone?	string	—

Returns

number of shared calendar dates, 0 when disjoint, or null on invalid input

Examples

intervalOverlappingDaysUnix(0, 172800000, 86400000, 259200000, { timeZone: "UTC" }) // 2
intervalOverlappingDaysUnix(0, 86400000, 86400000, 172800000, { timeZone: "UTC" }) // 1 (adjacent)
intervalOverlappingDaysUnix(0, 86400000, 172800000, 259200000, { timeZone: "UTC" }) // 0 (disjoint)
intervalOverlappingDaysUnix(NaN, 172800000, 86400000, 259200000, { timeZone: "UTC" }) // null

Source

unix/interval/intervalOverlappingDaysUnix.ts