For a while ago I needed to provide an alternative solution when Silverlight isn’t installed. I searched  for javascript code for this and found this:

• A blog post about that: Piotr Puszkiewicz’s Silverlight Blog. Determining if Silverlight is installed using Javascript.
• A more advanced javascript function which can even determine the version of the Silerlight can be pulled from Silverlight.js library.

I didn’t need to determine the version of Silverlight, so I wrote a simplified js function (but it works in all browsers):