Is It Time for the JavaScript Temporal API?
Tags: javascript, programming, webdev, beginners
Published: 2021-12-26 07:40:03

_by author [Craig Buckler](https://blog.openreplay.com/authors/craig-buckler)_

Date handling in JavaScript is *ugly*. The [`Date()` object](https://developer.mozilla.org/Web/JavaScript/Reference/Global_Objects/Date) 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:

```js
const today = new Date();
const tomorrow = new Date( today.setDate( today.getDate() + 1 ) );

console.log( tomorrow );  // is tomorrow's date
console.log( today );     // is also tomorrow's date!
```

Developers often turn to date libraries such as [moment.js](https://momentjs.com/) but it's a 74Kb payload and dates remain mutable. Modern alternatives such as [Day.js](https://day.js.org/) and [date-fns](https://date-fns.org/) 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](https://tc39.es/proposal-temporal/) (the final stage before implementation). The API addresses all the issues above and it's [coming to the Chrome browser soon](https://chromestatus.com/feature/5668291307634688). It's unlikely to have widespread implementation until late 2022 so be wary that changes could occur.


## Current Date and Time

[`Temporal.Now`](https://tc39.es/proposal-temporal/docs/#Temporal-Now) returns an object representing the current date and time. Further methods provide information such as:

```javascript
// time since the Unix epoch on 1 Janary, 1970 UTC
Temporal.Now.instant().epochSeconds;
Temporal.Now.instant().epochMilliseconds;

// time in current location
Temporal.Now.zonedDateTimeISO();

// current time zone
Temporal.Now.timeZone();

// current time in another time zone
Temporal.Now.zonedDateTimeISO('Europe/London');
```


## Instant Dates and Times

[`Temporal.Instant`](https://tc39.es/proposal-temporal/docs/#Temporal-Instant) returns an object representing a date and time to the nearest nanosecond according to an ISO 8601 formatted string:

![Temporal date time string](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/e6y8wfeslooq7fcl88vw.png)

```javascript
Temporal.Instant.from('2022-03-04T05:56:78.999999999+02:00[Europe/Berlin]');
Temporal.Instant.from('2022-03-04T05:06+07:00');
```

You can also use an epoch value:

```javascript
Temporal.Instant.fromEpochSeconds(1.0e8);
```


## Zoned Dates and Times

[`Temporal.ZonedDateTime`](https://tc39.es/proposal-temporal/docs/#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.

```javascript
new Temporal.ZonedDateTime(
  1234567890000, // epoch nanoseconds
  Temporal.TimeZone.from('Europe/London'), // timezone
  Temporal.Calendar.from('iso8601') // default calendar
);

Temporal.ZonedDateTime.from('2025-09-05T02:55:00+02:00[Africa/Cairo]');

Temporal.Instant('2022-08-05T20:06:13+05:45').toZonedDateTime('+05:45');

Temporal.ZonedDateTime.from({
  timeZone: 'America/New_York'
  year: 2025,
  month: 2,
  day: 28,
  hour: 10,
  minute: 15,
  second: 0,
  millisecond: 0,
  microsecond: 0,
  nanosecond: 0
});
```


## 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`](https://tc39.es/proposal-temporal/docs/#Temporal-PlainTime) refers to a specific time, e.g. "the meeting occurs at 3pm every weekday":

  ```javascript
  // both are 15:00:00
  new Temporal.PlainTime(15, 0, 0);
  Temporal.PlainTime.from('15:00:00');
  ```

* [`Temporal.PlainDate`](https://tc39.es/proposal-temporal/docs/#Temporal-PlainDate) refers to a specific date, e.g. "your tax return is due by January 31, 2022":

  ```javascript
  // both are January 31, 2022
  new Temporal.PlainDate(2022, 1, 31);
  Temporal.PlainDate.from('2022-01-31');
  ```

* [`Temporal.PlainDateTime`](https://tc39.es/proposal-temporal/docs/#Temporal-PlainDateTime) refers to a date and time without a time zone:

  ```javascript
  // both are 4 May 2022 at 10:11am and 12 seconds
  new Temporal.PlainDateTime(2022, 5, 4, 10, 11, 12);
  Temporal.PlainDateTime.from('2022-05-04T10:11:12');
  ```

* [`Temporal.PlainYearMonth`](https://tc39.es/proposal-temporal/docs/#Temporal-PlainYearMonth) refers to a date without a day, e.g. "the June 2022 schedule is ready":

  ```javascript
  // both are June 2022
  new Temporal.PlainYearMonth(2022, 6);
  Temporal.PlainYearMonth.from('2022-06');
  ```

* [`Temporal.PlainMonthDay`](https://tc39.es/proposal-temporal/docs/#Temporal-PlainMonthDay) refers to a date without a year, e.g. "Star Wars day is on May 4":

  ```javascript
  // both are May 4
  new Temporal.PlainMonthDay(5, 4);
  Temporal.PlainMonthDay.from('05-04');
  ```

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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:

```javascript
const t1 = Temporal.ZonedDateTime.from('2022-12-07T03:24:30+02:00[Africa/Cairo]');
```

you can extract:

```javascript
t1.year;        // returns 2022
t1.month;       // 12
t1.day;         // 7
t1.hour;        // 3
t1.minute;      // 24
t1.second;      // 30
t1.millisecond; // 0
t1.microsecond; // 0
t1.nanosecond;  // 0
```

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:

```javascript
const
  date1 = Temporal.Now,
  date2 = Temporal.PlainDateTime.from('2022-05-04');

Temporal.ZonedDateTime.compare(date1, date2);
// returns 1 when May 4, 2022 arrives
```

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

```javascript
const t = [

    '2022-01-01T00:00:00+00:00[Europe/London]',
    '2022-01-01T00:00:00+00:00[Africa/Cairo]',
    '2022-01-01T00:00:00+00:00[America/New_York]'

  ].map( d => Temporal.ZonedDateTime.from(d) )
  .sort( Temporal.ZonedDateTime.compare );
```


## Date and Time Calculations

All `Temporal` objects offer math methods to [add()](https://tc39.es/proposal-temporal/docs/duration.html#add), [subtract()](https://tc39.es/proposal-temporal/docs/duration.html#subtract), or [round()](https://tc39.es/proposal-temporal/docs/duration.html#round) to a duration.

You can define a duration as a [`Temporal.Duration` object](https://tc39.es/proposal-temporal/docs/duration.htm) 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:

```javascript
const t1 = Temporal.ZonedDateTime.from('2022-05-04T00:00:00+00:00[Europe/London]');

// add 8 hours 59 minutes
t1.add({ hours: 8, minutes: 59 }); // or
t1.add(Temporal.Duration.from({ hours: 8, minutes: 59 }));

// subtract 2 weeks
t1.subtract({ weeks: 2 }); // or
t1.add({ weeks: 2, sign: -1 });

// round to nearest month
t1.round({ smallestUnit: 'month' });
```

*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.

```javascript
// months to t1
t1.until().months;

// days to t2
t2.until().days;

// weeks since t3
t3.since().weeks;
```

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

```javascript
const
  d1 = Temporal.PlainDate.from('2022-01-31');
  d2 = Temporal.PlainDate.from('2023-01-31');

d1.equals(d2); // false
```


## Formatting Date and Time Strings

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

```javascript
2022-09-05T02:55:00+02:00[Europe/London]
```

This is not user friendly but the [Internationalization API](https://blog.openreplay.com/the-complete-guide-to-localizing-your-app-with-javascript-s-internationalization-api) offers a better alternative with localisation options. For example:

```javascript
// define a date
const d = new Temporal.PlainDate(2022, 3, 14);

// US date format: 3/14/2022
new Intl.DateTimeFormat('en-US').format(d);

// UK date format: 14/03/2022
new Intl.DateTimeFormat('en-GB').format(d);

// Spanish long date format: miércoles, 14 de abril de 2022
new Intl.DateTimeFormat('es-ES', { dateStyle: 'full' }).format(d);
```

This is not part of the `Temporal` API and there's no guarantee the [`Intl` (Internationalization) API](https://developer.mozilla.org/Web/JavaScript/Reference/Global_Objects/Intl) 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:

1. [The `Temporal` proposal](https://tc39.es/proposal-temporal/)
1. [The `Temporal` documentation](https://tc39.es/proposal-temporal/docs/)
1. [The `Temporal` cookbook examples](https://tc39.es/proposal-temporal/docs/cookbook.html)