JavaScript: The Definitive Guide, Fourth Edition

Name

Document.lastModified — the modification date of a document

Availability

JavaScript 1.0

Synopsis

                  document.lastModified

Description

lastModified is a read-only string property that contains the date and time at which document was most recently modified. This data is derived from HTTP header data sent by the web server. The web server generally obtains the last-modified date by examining the modification date of the file itself.

Web servers are not required to provide last-modified dates for the documents they serve. When a web server does not provide a last-modified date, JavaScript assumes 0, which translates to a date of midnight, January 1, 1970, GMT. The following example shows how you can test for this case.

Example

It is a good idea to let readers know how recent the information you provide on the Web is. You can include an automatic timestamp in your documents by placing the following script at the end of each HTML file. Doing this means you do not need to update the modification time by hand each time you make a change to the file. Note that this script tests that the supplied date is valid before displaying it:

<script>
if (Date.parse(document.lastModified) != 0)
    document.write('<p><hr><small><i>Last modified: '
                   + document.lastModified
                   + '</i></small>');
</script>

See Also

The Document location, referrer, and title properties