Last Updated Script

The "last updated" script automatically resets the displayed date on a web page each time the html source document is modified in any way. This script consist of only two lines of JavaScript code:
  var LastUpdated = document.lastModified;
  document.writeln ("This page was last updated " + LastUpdated);
 
The Structure: The JavaScript code goes into to the body of the html document at the point where it is to be displayed. It is inserted within a pair of html <script> tags. The opening script tag includes the attribute language="JavaScript" to distinguish it from other possible scripting languages (such as JScript or VBScript). The code is embedded within html comment tags (<!--   ......   -->), to hide it from older browsers that can't interpret JavaScript Code - otherwise the code will show up on the web page when viewed by non-JavaScript enabled browsers. JavaScript comments are preceded by two slashes //. Upper Case is used for the html tags and lower case is used for most of the JavaScript code. The former convention is optional, while the latter is required; JavaScript is "case sensitive."

Here is the entire document structure with the JavaScript syntax highlighted:

<html>
<head></head>
<body>
 
<script language="JavaScript">
<!-- Hide JavaScript...
var LastUpdated = document.lastModified;
document.writeln ("This page was last updated " + LastUpdated);
// End Hiding -->
</script>
 
</body>
</html>

The Code: I'll start with a simpler version of the code... The same code could have been written in one line, like this:
 document.writeln ("This page was last updated"+document.lastModified);  
      "document.writeln( )" is a predefined Javascript method that writes whatever is within the parentheses onto the displayed web page. The portion within the quotation marks can contain any user-defined value such as "Last Updated" or "Last Modified".
      "document.lastModified" is a JavaScript property which evaluates to the date and time that the html source document was last opened and altered.
      " + " is an operator which is used to connect or "concatonate" the two values within the parentheses.

Now for the two-line version of the code:
  var LastUpdated = document.lastModified;
  document.writeln ("This page was last updated " + LastUpdated);
The first line of this version is a variable statement. " var " signals that a new user-defined variable is being created. LastUpdated is an arbitrary (user-defined) name for the variable, essentially it is used as a shortcut for the "document.lastModified" property in the subsequent statement.