Dates - Errors

Every refusal is a coded RangeError or TypeError built with createErrors from @semantic-ui/utils. It is one line in production, with the way out appended in development.

Shape

dates refused [notADate] 2026

The error carries the code and the input it refused as properties, so a handler branches on the code rather than the text.

try {
  date(2026);
}
catch (error) {
  error.code; // 'notADate'
  error.at; // '2026'
  error instanceof TypeError; // true
}

A TypeError says the value is the wrong kind of thing. A RangeError says it is the right kind but cannot be read or done. { loose: true } turns the reading refusals into null and leaves the rest to throw. See Reading Values.

Reading

Code	Class	When
`notADateTime`	TypeError	`datetime()` given nothing, null, or a value of a kind it cannot read
`notADate`	TypeError	`date()` given nothing, a bare number, or a kind it cannot read. A RangeError for an instant string carrying `Z` or an offset, since the text is a date’s shape read in the wrong kind
`notATime`	TypeError	`time()` given nothing or a kind it cannot read
`notADuration`	TypeError	`duration()` given a kind it cannot read, or a duration beside a unit
`notAPoint`	TypeError	`compare()`, `earliest()` or `latest()` given a value that is not a point
`unreadableDateTime`	RangeError	text or fields that do not read as a datetime, `datetime('banana')`
`unreadableDate`	RangeError	text, numbers or fields that do not read as a date, `date(2026, 2, 30)`
`unreadableTime`	RangeError	text, numbers or fields that do not read as a time, `time('25:00')`
`unreadableDuration`	RangeError	text or fields that do not read as a length, `duration('banana')`
`notFinite`	RangeError	an invalid `Date`, `NaN` or an infinite number
`fractionalMonth`	RangeError	a fraction of a month or year, `duration('1.5 months')`
`mixedSigns`	RangeError	a phrase or fields with both signs, `duration('1h -30m')`, or a subtraction that would produce them

Zones and Locales

Code	Class	When
`unknownZone`	RangeError	a name that is not a zone, in a factory, `in()`, `configure({ zone })` or `configure({ zoneAliases })`
`unknownLocale`	RangeError	a locale Intl cannot read, in `configure({ locale })` or a `format()` call
`noZone`	RangeError	`timeRange.in(zone)`, since a time range has no zone to place in

Units

Code	Class	When
`unknownUnit`	RangeError	a unit name that is not one, `plus(7, 'fortnights')`
`unknownWeekday`	RangeError	a weekday name that is not one, `next('someday')`
`notADateUnit`	RangeError	a clock unit on a date, `date.plus(hours(3))` or `date.startOf('hour')`
`notATimeUnit`	RangeError	a calendar unit on a time, `time.plus(days(1))`, since a clock has no days
`emptyStep`	RangeError	a zero-length step in `points()` or `split()`

Arithmetic

Code	Class	When
`cannotAdd`	RangeError	`plus()` when Temporal refuses the sum underneath, a result outside the representable range
`cannotSubtract`	RangeError	`minus()` when Temporal refuses the difference underneath
`cannotSet`	RangeError	`set()` with a part out of range, `set('minute', 60)` or `set({ day: 31 })` in a short month
`cannotRound`	RangeError	`round()`, `floor()` or `ceil()` with a unit or increment the value cannot snap to
`cannotBalance`	RangeError	`balance()` when Temporal refuses the carry underneath
`cannotTotal`	RangeError	`total()` or `toMilliseconds()` when Temporal refuses the total underneath
`needsAnchor`	RangeError	months or years asked to total, balance, compare or become a number without a duration from `until()`
`calendarDuration`	RangeError	a duration counting months or years asked for its key by a schema, anchored or not, since their length depends on a calendar that does not travel. See Schema
`immutable`	RangeError	a `Date` setter on a datetime, `setHours(9)`. `set()` and `plus()` give a new value

Ranges

Code	Class	When
`backwards`	RangeError	a date or datetime range whose end comes before its start
`mixedRange`	TypeError	a range of one kind given where another is expected, `week.contains(datetimeRange(...))`
`twoPieces`	RangeError	an intersection across midnight that comes out in two pieces
`mixedKinds`	TypeError	`compare()` across kinds, `compare(date, datetime)`
`noPoints`	RangeError	`earliest()` or `latest()` given nothing

Formatting

Code	Class	When
`unknownFormat`	RangeError	a `format()` spec that is not a preset, an Intl options object or a token pattern, or an Intl options object Intl refuses
`noField`	RangeError	a token the kind has no field for, `date.format('HH:mm')`
`noTokens`	RangeError	a token pattern given to a range, which formats with a preset or Intl options

Numbers

Code	Class	When
`notANumber`	RangeError	`valueOf()` on a date, a time or a range, so `due < now()` throws rather than being silently true, while `'Due ' + due` gives the string

Runtime

Code	Class	When
`noTemporal`	RangeError	the first call on a runtime without `Temporal`. See Temporal Support

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