# localDateTimeToInstant

> Converts a local date and time in an IANA time zone to an RFC 3339 instant carrying the zone's offset at that local time.

> **localDateTimeToInstant**(`local`, `timeZone`): `string` \| `undefined`

Converts a local date and time in an IANA time zone to an RFC 3339 instant
carrying the zone's offset at that local time.

## Parameters

### local

`string`

`YYYY-MM-DDTHH:mm[:ss]`.

### timeZone

`string`

IANA zone name.

## Returns

`string` \| `undefined`

The instant (`2026-07-15T12:00:00-04:00`), or `undefined` when the
  zone or the local string is invalid. A local time that happens twice
  (clocks go back) resolves to its first occurrence, with the offset before
  the change. A local time that never happens (clocks go forward) takes the
  offset in force before the change, so `02:30` in a spring-forward gap in
  New York is `02:30:00-05:00`.