ISO, Date, Temporal and codecs

Choose the correct date representation and validate or transform it without ambiguity.

Three different domains

Schema	Runtime value	Choose it for
`JIT.iso.*`	string	JSON/forms/headers/database text
`JIT.date()`	native Date	existing JS APIs and SDKs
`JIT.temporal.*`	Temporal object	explicit calendar/time-zone semantics

Keeping these separate prevents hidden parsing and timezone conversion.

ISO namespace

JIT.iso.date();
JIT.iso.time({ precision: -1 });
JIT.iso.datetime({ offset: true, precision: 3 });
JIT.iso.duration();

All infer string. They append the same check nodes as the legacy JIT.string().date/time/datetime/duration methods, which remain supported.

Datetime options

default: requires Z;
offset: true: also accepts +HH:MM and -HH:MM;
local: true: also accepts no zone designator;
precision: -1: exact minute precision;
precision: 0: exact seconds;
precision: n: exact fractional digits.

const UtcMillis = JIT.iso.datetime({ precision: 3 });
const PartnerTimestamp = JIT.iso.datetime({ offset: true });
const AppointmentWallTime = JIT.iso.datetime({ local: true, precision: -1 });

Use local datetimes only when a timezone is carried separately. Transport events normally require UTC or an explicit offset.

Date operators

const DateInWindow = JIT.date()
  .between("2026-01-01T00:00:00.000Z", "2026-12-31T23:59:59.999Z")
  .daysOfWeek([1, 2, 3, 4, 5])
  .monthsOfYear([1, 2, 3, 4, 5, 6])
  .truncateTo("minute");

min, max and between are inclusive. Weekdays use JS numbering (0 is Sunday); months use 1..12. Truncation rejects non-zero lower fields.

instant, plainDate, plainTime, plainDateTime, zonedDateTime, plainYearMonth, plainMonthDay, and duration validate their matching Temporal constructors. Date-like checks are available where meaningful.

The test suite installs @js-temporal/polyfill. Applications must provide a polyfill on hosts without native Temporal.

Bidirectional codecs

const IsoToDate = JIT.codec(JIT.iso.datetime(), JIT.date(), {
  decode: (text) => new Date(text),
  encode: (date) => date.toISOString(),
});

Codecs validate both input/output schemas around the transform. They model a domain conversion; JIT.codec(schema, { version }) for bytes is a different transport API.

Performance model

ISO regexes are created while building/compiling the schema. The generated hot path performs a type gate and regex test without allocating Date/Temporal objects. Date and Temporal checks compare existing fields/epoch values. Decode only once when the next layer truly needs a richer object.