@github/time-elements

<relative-time> element

Formats a timestamp as a localized string or as relative text that auto-updates in the user's browser.

This allows the server to cache HTML fragments containing dates and lets the browser choose how to localize the displayed time according to the user's preferences. For example, the server may have cached the following generated markup:

<local-time datetime="2014-04-01T16:30:00-08:00">
  April 1, 2014 4:30pm
</local-time>

Every visitor is served the same markup from the server's cache. When it reaches the browser, the custom local-time JavaScript localizes the element's text into the local timezone and formatting.

<local-time datetime="2014-04-01T16:30:00-08:00">
  1 Apr 2014 21:30
</local-time>

Dates are displayed before months, and a 24-hour clock is used, according to the user's browser settings.

If the browser's JavaScript is disabled, the default text served in the cached markup is still displayed.

Installation

Available on npm as @github/time-elements.

$ npm install @github/time-elements

Usage

This component provides three custom subtypes of the standard HTML <time> element. All custom time elements MUST have a datetime attribute set to an ISO 8601 formatted timestamp.

relative-time

A relative time-ago-in-words description can be generated by using the relative-time element extension.

Add a <relative-time> element to your markup. Provide a default formatted date as the element's text content (e.g. April 1, 2014).

<relative-time datetime="2014-04-01T16:30:00-08:00">
  April 1, 2014
</relative-time>

Depending on how far in the future this is being viewed, the element's text will be replaced with one of the following formats:

• 6 years from now
• 20 days from now
• 4 hours from now
• 7 minutes from now
• just now
• 30 seconds ago
• a minute ago
• 30 minutes ago
• an hour ago
• 20 hours ago
• a day ago
• 20 days ago
• on Apr 1, 2014

So, a relative date phrase is used for up to a month and then the actual date is shown.

Attributes

Property Name	Attribute Name	Possible Values	Default Value
datetime	datetime	string	-
format	format	'auto'|'micro'|'elapsed'|string	'auto'
date	-	Date | null	-
tense	tense	'auto'|'past'|'future'	'auto'
precision	precision	'year'|'month'|'day'|'hour'|'minute'|'second'	'second'
threshold	threshold	string	'P30D'
prefix	prefix	string	'on'
second	second	'numeric'|'2-digit'|undefined	undefined
minute	minute	'numeric'|'2-digit'|undefined	undefined
hour	hour	'numeric'|'2-digit'|undefined	undefined
weekday	weekday	'short'|'long'|'narrow'|undefined	undefined
day	day	'numeric'|'2-digit'|undefined	'numeric'
month	month	'numeric'|'2-digit'|'short'|'long'|'narrow'|undefined	'short'
year	year	'numeric'|'2-digit'|undefined	'numeric'*
timeZoneName	time-zone-name	'long'|'short'|'shortOffset'|'longOffset'|'shortGeneric'|'longGeneric'|undefined	undefined

^*: If unspecified, year will return 'numeric' if datetime represents the same year as the current year. It will return undefined if unspecified and if datetime represents a different year to the current year.

datetime (string)

This is the datetime that the element is meant to represent. This must be a valid ISO8601 DateTime. It is also possible to use the date property on the element to set the date. el.date expects a Date object, while el.datetime expects a string. Setting one will override the other.

<relative-time datetime="2014-04-01T16:30:00-08:00" tense="past">
  April 1, 2038 <!-- Will display "now" until April 1 2038 at 16:30:01! -->
</relative-time>
<script>
  const el = document.querySelector('relative-time')
  console.assert(el.date.toISOString() === el.datetime)
  el.date = new Date()
  console.assert(el.datetime !== "2014-04-01T16:30:00-08:00")
</script>

format ('auto'|'micro'|'elapsed'|string, default: 'auto')

The default format is auto, but this can be changed to micro or elapsed.

The default auto format will display dates relative to the current time (unless they are past the threshold value - see below). The values are rounded to display a single unit, for example if the time between the given datetime and the current wall clock time exceeds a day, then the format will only ouput in days, and will not display hours, minutes or seconds.

The micro format which will display relative dates (within the threshold) in a more compact format. Similar to auto, the micro format rounds values to the nearest largest value. Additionally, micro format will not round lower than 1 minute, as such a datetime which is less than a minute from the current wall clock time will display '1m'.

The elapsed format will always non-rounded units of time, where any non-zero unit of time is displayed in the compact notation format. This format is also absolute, and so tense does not apply. This can be useful for displaying actively running timers.

format=auto	format=micro	format=elapsed
in 2 years	2y	2y 10d 3h 20m 8s
2 years ago	2y	2y 10d 3h 20m 8s
in 30 days	30d	30d 4h 20m 8s
21 minutes ago	21m	21m 30s
37 seconds ago	1m	37s

Additionally, format accepts a strftime compatible format. Providing a strftime format will override all other attributes on the element, and the time will be displayed formatted based on the strftime value. This can be useful, for example, to dynamically remove relative formatting based on a user action.

<relative-time datetime="1970-04-01T16:30:00-08:00" threshold="P100Y" format="micro">
  <!-- Will display "<N>y" -->
</relative-time>

<relative-time datetime="1970-04-01T16:30:00-08:00" format="%Y-%m-%d">
  <!-- Will display "1970-01-01" -->
</relative-time>

tense ('auto'|'past'|'future', default: auto)

If format is anything other than 'auto' or 'micro' then this value will be ignored.

Tense can be used to fix relative-time to always display a date's relative tense in the future or the past. Setting tense=past will always display future dates as now, while setting it to future will always display past dates as now.

<relative-time datetime="2038-04-01T16:30:00-08:00" tense="past">
  April 1, 2038 <!-- Will display "now" until April 1 2038 at 16:30:01! -->
</relative-time>

<relative-time datetime="1970-04-01T16:30:00-08:00" tense="future">
  April 1, 2038 <!-- Will display "now" unless you had a time machine and went back to 1970 -->
</relative-time>

precision ('year'|'month'|'day'|'hour'|'minute'|'second', default: 'second')

If format is anything other than 'elapsed' then this value will be ignored.

Precision can be used to limit the display of an elapsed formatted time. By default the elapsed time will display times down to the second level of precision. Changing this value will truncate the display to the respective unit, and smaller units will be elided. Some examples:

precision=	Display
seconds	2y 6m 10d 3h 20m 8s
minutes	2y 6m 10d 3h 20m
hours	2y 6m 10d 3h
days	2y 6m 10d
months	2y 6m
years	2y

threshold (string, default: P30D)

If tense is anything other than 'auto' or format is anything other than 'auto' or 'micro' then this value will be ignored.

Threshold can be used to specify when a relative display (e.g. "5 days ago") should turn into an absolute display (i.e. the full date). This should be a valid ISO8601 Time Duration. If the difference between the current time and the specified datetime is more than the duration, then the date will be displayed as an absolute value (i.e. the full date), otherwise it will be formatted to a relative display (e.g. "5 days ago").

The default value for this is P30D, meaning if the current time is more than 30 days away from the specified date time, then an absolute date will be displayed.

<relative-time datetime="1970-04-01T16:30:00-08:00" threshold="P100Y">
  <!-- Will display "<N> years ago" until 2070 when it will display "on April 1, 1970" -->
</relative-time>

<relative-time datetime="1970-04-01T16:30:00-08:00" threshold="P0S">
  <!-- Will always display "on April 1, 1970" -->
</relative-time>

prefix (string, default: 'on')

If tense is anything other than 'auto' or format is anything other than 'auto' or 'micro' then this value will be ignored.

When formatting an absolute date (see above threshold for more details) it can be useful to prefix the date with some text. The default value for this is on but it can be any string value, an will be prepended to the date.

<relative-time datetime="1970-04-01T16:30:00-08:00" prefix="this happened on">
  <!-- Will always display "this happened on April 1, 1970" -->
</relative-time>

second, minute, hour, weekday, day, month, year, timeZoneName

For dates outside of the specified threshold, the formatting of the date can be configured using these attributes. The values for these attributes are passed to Intl.DateTimeFormat:

lang

Lang is a built-in global attribute. Relative Time will use this to provide an applicable language to the Intl APIs. If the individual element does not have a lang attribute then it will traverse upwards in the tree to find the closest element that does, or default the lang to en.

Additional Elements

In addition to <relative-time> this package provides convenience elements, which are configurations over <relative-time>. These additional elements will be removed in a future major version release.

time-until

This element is the same as <relative-time tense="future">. .tense will always return future, regardless of the value set in the attribute.

You can use time-until to always display a relative date that's in the future. It operates much like <relative-time>, except in the reverse, with past events shown as just now and future events always showing as relative:

• in 10 years
• in 20 days
• in 6 hours
• in 20 minutes
• in 30 seconds
• just now

Add a <time-until> element to your markup. Provide a default formatted date as the element's text content (e.g. April 1, 2024).

<time-until datetime="2024-04-01T16:30:00-08:00">
  April 1, 2024
</time-until>

Micro format

The optional format="micro" attribute shortens the descriptions to 1m, 1h, 1d, 1y.

<time-until datetime="2012-04-01T16:30:00-08:00" format="micro">
  April 1, 2014
</time-until>

time-ago

This element is the same as <relative-time tense="past">. .tense will always return past, regardless of the value set in the attribute.

An always relative time-ago-in-words description can be generated by using the time-ago element extension. This is similar to the relative-time extension. However, this will never switch to displaying the date. It strictly shows relative date phrases, even after a month has passed.

<time-ago datetime="2012-04-01T16:30:00-08:00">
  April 1, 2014
</time-ago>

For example, if this markup is viewed two years in the future, the element's text will read 2 years ago.

Micro format

The optional format="micro" attribute shortens the descriptions to 1m, 1h, 1d, 1y.

<time-ago datetime="2012-04-01T16:30:00-08:00" format="micro">
  April 1, 2014
</time-ago>

local-time

This is a variation of <relative-time> with some subtly different formatting.

This custom time extension is useful for formatting a date and time in the user's preferred locale format.

<local-time datetime="2014-04-01T16:30:00-08:00"
    month="short"
    day="numeric"
    year="numeric"
    hour="numeric"
    minute="numeric">
  April 1, 2014 4:30PM PDT
</local-time>

When this markup is viewed in a CDT timezone, it will show Apr 1, 2014 6:30PM. If it's viewed in a browser with European date preferences, it will read 1 Apr 2014 18:30.

Browser Support

Browsers without native custom element support require a polyfill.

• Chrome
• Firefox
• Safari
• Microsoft Edge

See Also

Most of this implementation is based on Basecamp's local_time component. Thanks to @javan for open sourcing that work and allowing for others to build on top of it.

@rmm5t's jquery-timeago is one of the old time-ago-in-words JS plugins.