While date/time information items have to be formatted as strings in a human-readable form on web pages, preferably in localized form based on the settings of the user's browser, it's not a good idea to store date/time values in this form. Rather, we use instances of the pre-defined JavaScript class Date for representing and storing date/time values. In this form, the pre-defined functions toISOString() and toLocaleDateString() can be used for turning Date values into ISO standard date/time strings (of the form "2015-01-27") or to localized date/time strings (like "27.1.2015"). Notice that, for simplicity, we have omitted the time part of the date/time strings.
In summary, a date/time value is expressed in three different forms:
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Internally, for storage and computations, as a Date value.
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Internally, for annotating localized date/time strings, or externally, for displaying a date/time value in a standard form, as an ISO standard date/time string, e.g., with the help of toISOString().
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Externally, for displaying a date/time value in a localized form, as a localized date/time string, e.g., with the help of toLocaleDateString().
When a date/time value is to be included in a web page, we can use the <time> element that allows to display a human-readable representation (typically a localized date/time string) that is annotated with a standard (machine-readable) form of the date/time value.
We illustrate the use of the element with the following example of a web page that includes two elements: one for displaying a fixed date, and another (initially empty) element for displaying the date of today, which is computed with the help of a JavaScript function. In both cases, we use the datetime attribute for annotating the displayed human-readable date with the corresponding machine-readable representation.
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="UTF-8" />
<title>Using the HTML5 Time Element</title>
<script>
function assignDate() {
var dateEl = document.getElementById("today");
var today = new Date();
dateEl.textContent = today.toLocaleDateString();
dateEl.setAttribute("datetime", today.toISOString());
}
window.addEventListener("load", assignDate);
</script>
</head>
<body>
<h1>HTML5 Time Element</h1>
<p>HTML 2.0 was published on
<time datetime="1995-11-24">24.11.1995</time>.</p>
<p>Today is <time id="today" datetime=""></time>.</p>
</body>
</html>
After this web page is loaded, the JavaScript function assignDate() is executed. It computes today's date as a Date value and assigns the ISO standard representation to the element's datetime attribute and the localized representation as the text content of the element.
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