opening Outlook through javascript

You can definitely do this, the code looks like:

var objO = new ActiveXObject('Outlook.Application');     
var objNS = objO.GetNameSpace('MAPI');     
var mItm = objO.CreateItem(0);     
mItm.Display();     
mItm.To = p_recipient;
mItm.Subject = p_subject;
mItm.Body = p_body;     
mItm.GetInspector.WindowState = 2;

p_recipient, p_subject & p_body being variables, passed in.

You need to ensure this is running on a webpage which users trust, as this will cause exceptions otherwise.
That is it needs to be in the right zone in IE, with the right settings configured for that zone.

You cannot open desktop applications through JavaScript for very obvious security reasons. The example you gave uses ActiveX which is a proprietary Microsoft technology only available in Internet Explorer.

If you simply want to open a message composition in a users email client with fields pre-filled, you can use the mailto: hyperlink prefix. This allows you to specify recipients, subject and body. Example:

<a href="mailto:[email protected]?subject=You can specify subject too">

Unless you have a requirement to specifically use Outlook (and I'd suggest you may want to revisit your requirements if that's the case), it is far more desirable to open whatever the default email client the user has set.