API / Functions

`kindOf()` function

Identify and narrow native-dates values across realms and bundle copies.

import { kindOf, isDateTime } from 'native-dates'core 7.3 kB min+br

Reading a value’s kind

`kindOf()`

kindOf(value):
  | 'datetime' | 'date' | 'time' | 'duration'
  | 'dateRange' | 'datetimeRange' | 'timeRange'
  | undefined

Returns a string tag naming which type a value belongs to, or undefined for plain JavaScript values such as native dates, strings, numbers, and objects. Also identifies range instances when @native-dates/plugins/ranges is loaded.

inspect.js

import { date, hours, kindOf, now, time } from 'native-dates';
import { dateRange } from '@native-dates/plugins/ranges';

kindOf(now()); // 'datetime'
kindOf(date('2026-11-16')); // 'date'
kindOf(time('9:30am')); // 'time'
kindOf(hours(2)); // 'duration'
kindOf(dateRange('2026-11-01', '2026-11-07')); // 'dateRange'
kindOf(new Date()); // undefined

Parameters

valueunknownrequired

Any value to inspect.

Returns

String tag for the value's kind, or undefined when value is not from this library.

Type guards

Type guards check global symbol brands rather than prototype identity. Guards for range types are exported by @native-dates/plugins/ranges.

`isDateTime()`

isDateTime(value): value is DateTime

Returns true when the value is a DateTime instance, narrowing its type in TypeScript.

import { datetime, isDateTime } from 'native-dates';

const stamp = datetime('2026-11-16T17:30:00Z');
isDateTime(stamp); // true
isDateTime('2026-11-16T17:30:00Z'); // false

`isCalendarDate()`

isCalendarDate(value): value is CalendarDate

Returns true when the value is a CalendarDate instance, narrowing its type in TypeScript.

import { date, isCalendarDate } from 'native-dates';

isCalendarDate(date('2026-11-16')); // true
isCalendarDate(new Date()); // false

`isTime()`

isTime(value): value is Time

Returns true when the value is a Time instance, narrowing its type in TypeScript.

import { isTime, time } from 'native-dates';

isTime(time('9:30am')); // true

`isDuration()`

isDuration(value): value is Duration

Returns true when the value is a Duration instance, narrowing its type in TypeScript.

import { hours, isDuration } from 'native-dates';

isDuration(hours(2)); // true

Cross-realm instanceof and brands

Standard JavaScript instanceof checks fail across iframe boundaries and duplicate bundled copies. Every class here implements [Symbol.hasInstance] over a global registry symbol, so both instanceof and the guard functions work across realms.

You can also read the exported brand symbols directly when writing custom serializers, test matchers, or generic helpers that detect ranges without importing the ranges plugin:

import { DateTime, IS_DATE_TIME, IS_RANGE, now } from 'native-dates';
import { timeRange } from '@native-dates/plugins/ranges';

const current = now();
current instanceof DateTime; // true
Boolean(current[IS_DATE_TIME]); // true

const shift = timeRange('9am', '5pm');
Boolean(shift[IS_RANGE]); // true

Constant	Global symbol key	Matches
`IS_DATE_TIME`	`Symbol.for('native-dates/DateTime')`	Matches any DateTime instance.
`IS_CALENDAR_DATE`	`Symbol.for('native-dates/CalendarDate')`	Matches any CalendarDate instance.
`IS_TIME`	`Symbol.for('native-dates/Time')`	Matches any Time instance.
`IS_DURATION`	`Symbol.for('native-dates/Duration')`	Matches any Duration instance.
`IS_RANGE`	`Symbol.for('native-dates/Range')`	Matches DateRange, DateTimeRange, and TimeRange instances.
`IS_DATE_RANGE`	`Symbol.for('native-dates/DateRange')`	Matches DateRange instances.
`IS_DATE_TIME_RANGE`	`Symbol.for('native-dates/DateTimeRange')`	Matches DateTimeRange instances.
`IS_TIME_RANGE`	`Symbol.for('native-dates/TimeRange')`	Matches TimeRange instances.

Edit this pageUpdated Nov 12, 2026

kindOf() function

Reading a value’s kind

kindOf()

Type guards

isDateTime()

isCalendarDate()

isTime()