launch app from browser

[Lars Brehmer]

Quick, easy question;

I need to launch a standalone from within a web browser, but I know  
absolutely zero html etc.  This would be an html file either  
installed on a user's hard drive or being read from a CD-rom with  
Firefox, Explorer, Safari, etc.  The standalone is already installed  
on the hard drive. In rev the button script is simply;

on mouseUp
   if the platform is "macOS" then
     launch "/applications/eestikeeluus.app"
   else
     launch "C:\Program Files\eestiKeel\eestiKeel.exe"
   end if
end mouseUp

How do I script a  button in this html file to do the same thing?  
Please remember, I know no html.

Cheers,

Lars