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Is It Time for the JavaScript Temporal API?

December 26th, 2021 · 3 min read

Date handling in JavaScript is ugly. The Date() object has not changed since the first Java-inspired implementation in 1995. Java scrapped it but Date() remained in JavaScript for backward browser compatibility.

Issues with the Date() API include:

• it’s inelegant
• it only supports UTC and the user’s PC time
• it doesn’t support calendars other than Gregorian
• string to date parsing is error-prone
• Date objects are mutable — for example:

Developers often turn to date libraries such as moment.js but it’s a 74Kb payload and dates remain mutable. Modern alternatives such as Day.js and date-fns may be better but should a library necessary when your app has minimal date-handling requirements?

Browsers must continue to support Date() but a new Temporal static global date object is at the Stage 3 Candidate Proposal in the TC39 standards approval process (the final stage before implementation). The API addresses all the issues above and it’s coming to the Chrome browser soon. It’s unlikely to have widespread implementation until late 2022 so be wary that changes could occur.

Current Date and Time

Temporal.Now returns an object representing the current date and time. Further methods provide information such as:

Instant Dates and Times

Temporal.Instant returns an object representing a date and time to the nearest nanosecond according to an ISO 8601 formatted string:

You can also use an epoch value:

Zoned Dates and Times

Temporal.ZonedDateTime returns an object representing a timezone and calendar-aware date/time at the instant an event occurred (or will occur) in a particular global location, e.g.

Plain Dates and Times

Plain dates and times reference simpler calendar events which are not associated with a specific time zone. The options include:

• Temporal.PlainTime refers to a specific time, e.g. “the meeting occurs at 3pm every weekday”:

  1// both are 15:00:00

  2new Temporal.PlainTime(15, 0, 0);

  3Temporal.PlainTime.from('15:00:00');

• Temporal.PlainDate refers to a specific date, e.g. “your tax return is due by January 31, 2022”:

  1// both are January 31, 2022

  2new Temporal.PlainDate(2022, 1, 31);

  3Temporal.PlainDate.from('2022-01-31');

• Temporal.PlainDateTime refers to a date and time without a time zone:

  1// both are 4 May 2022 at 10:11am and 12 seconds

  2new Temporal.PlainDateTime(2022, 5, 4, 10, 11, 12);

  3Temporal.PlainDateTime.from('2022-05-04T10:11:12');

• Temporal.PlainYearMonth refers to a date without a day, e.g. “the June 2022 schedule is ready”:

  1// both are June 2022

  2new Temporal.PlainYearMonth(2022, 6);

  3Temporal.PlainYearMonth.from('2022-06');

• Temporal.PlainMonthDay refers to a date without a year, e.g. “Star Wars day is on May 4”:

  1// both are May 4

  2new Temporal.PlainMonthDay(5, 4);

  3Temporal.PlainMonthDay.from('05-04');

Open Source Session Replay

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Date and Time Values

You can extract specific date and time values from a Temporal object. Assuming the following date and time:

you can extract:

Other useful properties include:

• dayOfWeek — returns 1 for Monday to 7 for Sunday
• dayOfYear — returns 1 to 365 or 366 on leap years
• weekOfYear — returns 1 to 52 or 53
• daysInMonth — returns 28, 29, 30, or 31
• daysInYear — returns 365 or 366
• inLeapYear — returns true for a leap year or false when not

Comparing and Sorting Dates and Times

All Temporal objects have a .compare(date1, date2) method which returns:

• 0 when date1 and date2 are the same
• 1 when date1 occurs after date2, or
• -1 when date1 occurs before date2

For example:

You can pass the compare() method as an Array sort() function to arrange dates into ascending chronological order (earliest to latest):

Date and Time Calculations

All Temporal objects offer math methods to add(), subtract(), or round() to a duration.

You can define a duration as a Temporal.Duration object which sets a period in years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, and nanoseconds as well as a sign for -1 negative or 1 positive durations. However, all these methods accept a duration-like value without the need to create a specific object. Examples:

Plain dates and times can wrap so adding 24 hours to a PlainTime returns a new Temporal object with an identical value.

The until() and since() methods return a Temporal.Duration object describing the time until or since a specific date and time based on the current date/time, e.g.

The equals() method also determines whether two date/time values are identical:

Formatting Date and Time Strings

All Temporal objects have a string representation returned when using the .toString() method, e.g. Temporal.Now.toString():

This is not user friendly but the Internationalization API offers a better alternative with localisation options. For example:

This is not part of the Temporal API and there’s no guarantee the Intl (Internationalization) API will support Temporal as well as Date objects — although there would be a developer outcry if it didn’t!

Temporal Time

We’ve accepted the dodgy Date() since day one but Temporal gives JavaScript developers something to look forward to. The days of resorting to a date library are nearly over.

For further information, refer to: