Adding External Javascript in joomla

JDocument/addScript

Adds the definition of a linked external script to the document object. Duplicates are ignored.

Syntax

void addScript( $url, $type )
where:

Argument	Data type	Description	Default
$url	string	URL of script.
$type	string	MIME type of script.	'text/javascript'

Example

To add a link to some JavaScript code at a specific URL, you could use:

$doc =& JFactory::getDocument();
$doc->addScript("http://www.example.com/js/myscript.js"); 

How this is rendered depends on the document type. If the document type is HTML then this code will
 produce following link in the HTML HEAD section:

<script type="text/javascript" src="http://www.example.com/js/myscript.js"></script>

 source: http://docs.joomla.org/JDocument/addScriptDeclaration