Web component extensions to the standard
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Simon Taranto 26b72276a4
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<time> element extensions

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

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

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.


Available on npm as @github/time-elements.

$ npm install @github/time-elements


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.


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

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.


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:

  • 10 years from now
  • 20 days from now
  • 6 hours from now
  • 20 minutes from now
  • 30 seconds from now
  • 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


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

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


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"
  April 1, 2014 4:30PM PDT

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.


Attribute Options Description
datetime ISO 8601 date Required date of element 2014-06-01T13:05:07Z
year 2-digit, numeric Format year as 14 or 2014
month short, long Format month as Jun or June
day 2-digit, numeric Format day as 01 or 1
weekday short, long Format weekday as Sun or Sunday
hour 2-digit, numeric Format hour as 01 or 1
minute 2-digit, numeric Format minute as 05 or 5
second 2-digit, numeric Format second as 07 or 7
time-zone-name short, long Display time zone as GMT+1 or by its full name

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.