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:

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

Every user 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 to:

<time is="local-time" datetime="2014-04-01T16:30:00-08:00">
  1 Apr 2014 14:30
</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.

Available on Bower as time-elements.

$ bower install time-elements

This component is built on the upcoming Web Component stack. Specifically, it requires a feature called Custom Elements.

You'll need to use a polyfill to get this feature today. Either the Polymer or X-Tag frameworks supply a polyfill, or you can install the standalone CustomElements polyfill.

<script src="https://cdnjs.cloudflare.com/ajax/libs/webcomponentsjs/0.5.4/CustomElements.min.js"></script>

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.

Tag a standard <time> element with an is="relative-time" attribute in your markup. Provide a default formatted date as the element's text content (e.g. April 1, 2014).

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

• 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.

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

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

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

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

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

<time is="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
</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.

Latest ✔	Latest ✔	9+ ✔	Latest ✔	6.1+ ✔

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.