Temporal.PlainDateTime

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The Temporal.PlainDateTime object represents a date (calendar date) and time (wall-clock time) without a time zone. It is fundamentally represented as a combination of a date (with an associated calendar system) and a time.

Description

A PlainDateTime is essentially the combination of a Temporal.PlainDate and a Temporal.PlainTime. Because the date and time information don't have much interaction, all general information about date properties is documented in the PlainDate object, and all general information about time properties is documented in the PlainTime object.

If the date-time represents a specific instant that should remain invariant across time zones, you should use the Temporal.ZonedDateTime object instead. Use PlainDateTime when you need to represent an event happening at a specific wall-clock time that may be a different instant in different time zones.

RFC 9557 format

PlainDateTime objects can be serialized and parsed using the RFC 9557 format, an extension to the ISO 8601 / RFC 3339 format. The string has the following form (spaces are only for readability and should not be present in the actual string):

YYYY-MM-DD T HH:mm:ss.sssssssss [u-ca=calendar_id]

YYYY: Either a four-digit number, or a six-digit number with a + or - sign.
MM: A two-digit number from 01 to 12.
DD: A two-digit number from 01 to 31. The YYYY, MM, and DD components can be separated by - or nothing.
T Optional: The date-time separator, which can be T, t, or a space. Present if and only if HH is present.
HH Optional: A two-digit number from 00 to 23. Defaults to 00.
mm Optional: A two-digit number from 00 to 59. Defaults to 00.
ss.sssssssss Optional: A two-digit number from 00 to 59. May optionally be followed by a . or , and one to nine digits. Defaults to 00. The HH, mm, and ss components can be separated by : or nothing. You can omit either just ss or both ss and mm, so the time can be one of three forms: HH, HH:mm, or HH:mm:ss.sssssssss.
[u-ca=calendar_id] Optional: Replace calendar_id with the calendar to use. See Intl.supportedValuesOf() for a list of commonly supported calendar types. Defaults to [u-ca=iso8601]. May have a critical flag by prefixing the key with !: e.g., [!u-ca=iso8601]. This flag generally tells other systems that it cannot be ignored if they don't support it. The Temporal parser will throw an error if the annotations contain two or more calendar annotations and one of them is critical. Note that the YYYY-MM-DD is always interpreted as an ISO 8601 calendar date and then converted to the specified calendar.

As an input, you may optionally include the offset and time zone identifier, in the same format as ZonedDateTime, but they will be ignored. Note that the offset must not be Z. Other annotations in the [key=value] format are also ignored, and they must not have the critical flag.

When serializing, you can configure the fractional second digits, whether to display the calendar ID, and whether to add a critical flag for it.

Constructor

Temporal.PlainDateTime() Experimental: Creates a new Temporal.PlainDateTime object by directly supplying the underlying data.

Static methods

Temporal.PlainDateTime.compare() Experimental: Returns a number (-1, 0, or 1) indicating whether the first date-time comes before, is the same as, or comes after the second date-time. Equivalent to first comparing their dates, then comparing their times if the dates are the same.
Temporal.PlainDateTime.from() Experimental: Creates a new Temporal.PlainDateTime object from another Temporal.PlainDateTime object, an object with date and time properties, or an RFC 9557 string.

Instance properties

These properties are defined on Temporal.PlainDateTime.prototype and shared by all Temporal.PlainDateTime instances.

Temporal.PlainDateTime.prototype.calendarId Experimental: Returns a string representing the calendar used to interpret the internal ISO 8601 date.
Temporal.PlainDateTime.prototype.constructor: The constructor function that created the instance object. For Temporal.PlainDateTime instances, the initial value is the Temporal.PlainDateTime() constructor.
Temporal.PlainDateTime.prototype.day Experimental: Returns a positive integer representing the 1-based day index in the month of this date, which is the same day number you would see on a calendar. Calendar-dependent. Generally starts at 1 and is continuous, but not always.
Temporal.PlainDateTime.prototype.dayOfWeek Experimental: Returns a positive integer representing the 1-based day index in the week of this date. Days in a week are numbered sequentially from 1 to daysInWeek, with each number mapping to its name. Calendar-dependent. 1 usually represents Monday in the calendar, even when locales using the calendar may consider a different day as the first day of the week (see Intl.Locale.prototype.getWeekInfo()).
Temporal.PlainDateTime.prototype.dayOfYear Experimental: Returns a positive integer representing the 1-based day index in the year of this date. The first day of this year is 1, and the last day is the daysInYear. Calendar-dependent.
Temporal.PlainDateTime.prototype.daysInMonth Experimental: Returns a positive integer representing the number of days in the month of this date. Calendar-dependent.
Temporal.PlainDateTime.prototype.daysInWeek Experimental: Returns a positive integer representing the number of days in the week of this date. Calendar-dependent. For the ISO 8601 calendar, this is always 7, but in other calendar systems it may differ from week to week.
Temporal.PlainDateTime.prototype.daysInYear Experimental: Returns a positive integer representing the number of days in the year of this date. Calendar-dependent. For the ISO 8601 calendar, this is 365, or 366 in a leap year.
Temporal.PlainDateTime.prototype.era Experimental: Returns a calendar-specific lowercase string representing the era of this date, or undefined if the calendar does not use eras (e.g., ISO 8601). era and eraYear together uniquely identify a year in a calendar, in the same way that year does. Calendar-dependent. For Gregorian, it is either "gregory" or "gregory-inverse".
Temporal.PlainDateTime.prototype.eraYear Experimental: Returns a non-negative integer representing the year of this date within the era, or undefined if the calendar does not use eras (e.g., ISO 8601). The year index usually starts from 1 (more common) or 0, and years in an era can decrease with time (e.g., Gregorian BCE). era and eraYear together uniquely identify a year in a calendar, in the same way that year does. Calendar-dependent.
Temporal.PlainDateTime.prototype.hour Experimental: Returns a integer from 0 to 23 representing the hour component of this time.
Temporal.PlainDateTime.prototype.inLeapYear Experimental: Returns a boolean indicating whether this date is in a leap year. A leap year is a year that has more days (due to a leap day or leap month) than a common year. Calendar-dependent.
Temporal.PlainDateTime.prototype.microsecond Experimental: Returns a integer from 0 to 999 representing the microsecond (10^-6 second) component of this time.
Temporal.PlainDateTime.prototype.millisecond Experimental: Returns a integer from 0 to 999 representing the millisecond (10^-3 second) component of this time.
Temporal.PlainDateTime.prototype.minute Experimental: Returns a integer from 0 to 59 representing the minute component of this time.
Temporal.PlainDateTime.prototype.month Experimental: Returns a positive integer representing the 1-based month index in the year of this date. The first month of this year is 1, and the last month is the monthsInYear. Calendar-dependent. Note that unlike Date.prototype.getMonth(), the index is 1-based. If the calendar has leap months, then the month with the same monthCode may have different month indexes for different years.
Temporal.PlainDateTime.prototype.monthCode Experimental: Returns a calendar-specific string representing the month of this date. Calendar-dependent. Usually it is M plus a two-digit month number. For leap months, it is the previous month's code followed by L. If the leap month is the first month of the year, the code is M00L.
Temporal.PlainDateTime.prototype.monthsInYear Experimental: Returns a positive integer representing the number of months in the year of this date. Calendar-dependent. For the ISO 8601 calendar, this is always 12, but in other calendar systems it may differ.
Temporal.PlainDateTime.prototype.nanosecond Experimental: Returns a integer from 0 to 999 representing the nanosecond (10^-9 second) component of this time.
Temporal.PlainDateTime.prototype.second Experimental: Returns a integer from 0 to 59 representing the second component of this time.
Temporal.PlainDateTime.prototype.weekOfYear Experimental: Returns a positive integer representing the 1-based week index in the yearOfWeek of this date, or undefined if the calendar does not have a well-defined week system. The first week of the year is 1. Calendar-dependent. Note that for ISO 8601, the first and last few days of the year may be attributed to the last week of the previous year or the first week of the next year.
Temporal.PlainDateTime.prototype.year Experimental: Returns an integer representing the number of years of this date relative to the start of a calendar-specific epoch year. Calendar-dependent. Usually year 1 is either the first year of the latest era or the ISO 8601 year 0001. If the epoch is in the middle of the year, that year will have the same value before and after the start date of the era.
Temporal.PlainDateTime.prototype.yearOfWeek Experimental: Returns an integer representing the year to be paired with the weekOfYear of this date, or undefined if the calendar does not have a well-defined week system. Calendar-dependent. Usually this is the year of the date, but for ISO 8601, the first and last few days of the year may be attributed to the last week of the previous year or the first week of the next year, causing the yearOfWeek to differ by 1.
Temporal.PlainDateTime.prototype[Symbol.toStringTag]: The initial value of the [Symbol.toStringTag] property is the string "Temporal.PlainDateTime". This property is used in Object.prototype.toString().

Instance methods

Temporal.PlainDateTime.prototype.add() Experimental: Returns a new Temporal.PlainDateTime object representing this date-time moved forward by a given duration (in a form convertible by Temporal.Duration.from()).
Temporal.PlainDateTime.prototype.equals() Experimental: Returns true if this date-time is equivalent in value to another date-time (in a form convertible by Temporal.PlainDateTime.from()), and false otherwise. They are compared both by their date and time values and their calendars, so two date-times from different calendars may be considered equal by Temporal.PlainDateTime.compare() but not by equals().
Temporal.PlainDateTime.prototype.round() Experimental: Returns a new Temporal.PlainDateTime object representing this date-time rounded to the given unit.
Temporal.PlainDateTime.prototype.since() Experimental: Returns a new Temporal.Duration object representing the duration from another date-time (in a form convertible by Temporal.PlainDateTime.from()) to this date-time. The duration is positive if the other date-time is before this date-time, and negative if after.
Temporal.PlainDateTime.prototype.subtract() Experimental: Returns a new Temporal.PlainDateTime object representing this date-time moved backward by a given duration (in a form convertible by Temporal.Duration.from()).
Temporal.PlainDateTime.prototype.toJSON() Experimental: Returns a string representing this date-time in the same RFC 9557 format as calling toString(). Intended to be implicitly called by JSON.stringify().
Temporal.PlainDateTime.prototype.toLocaleString() Experimental: Returns a string with a language-sensitive representation of this date-time.
Temporal.PlainDateTime.prototype.toPlainDate() Experimental: Returns a new Temporal.PlainDate object representing the date part (year, month, day) of this date-time in the same calendar system.
Temporal.PlainDateTime.prototype.toPlainTime() Experimental: Returns a new Temporal.PlainTime object representing the time part (hour, minute, second, and subsecond components) of this date-time.
Temporal.PlainDateTime.prototype.toString() Experimental: Returns a string representing this date-time in the RFC 9557 format.
Temporal.PlainDateTime.prototype.toZonedDateTime() Experimental: Returns a new Temporal.ZonedDateTime instance representing the same date-time as this plain date-time, but in the specified time zone.
Temporal.PlainDateTime.prototype.until() Experimental: Returns a new Temporal.Duration object representing the duration from this date-time to another date-time (in a form convertible by Temporal.PlainDateTime.from()). The duration is positive if the other date-time is after this date-time, and negative if before.
Temporal.PlainDateTime.prototype.valueOf() Experimental: Throws a TypeError, which prevents Temporal.PlainDateTime instances from being implicitly converted to primitives when used in arithmetic or comparison operations.
Temporal.PlainDateTime.prototype.with() Experimental: Returns a new Temporal.PlainDateTime object representing this date-time with some fields replaced by new values.
Temporal.PlainDateTime.prototype.withCalendar() Experimental: Returns a new Temporal.PlainDateTime object representing this date-time interpreted in the new calendar system.
Temporal.PlainDateTime.prototype.withPlainTime() Experimental: Returns a new Temporal.PlainDateTime object representing this date-time with the time part entirely replaced by the new time (in a form convertible by Temporal.PlainTime.from()).

Specifications

Specification
Temporal # sec-temporal-plaindatetime-objects

Browser compatibility

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This page was last modified on ⁨Jul 10, 2025⁩ by MDN contributors.

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