You can't STRICTLY do this with CF alone as CF is a
server-side application.
I would recommend setting a cookie with JavaScript into a
users session, THEN use CF to try and read the cookie from the
users session. If the cookie doesn't exist, it clearly means that
JavaScript wasn't able to set a cookie, possibly meaning JS is
disabled.
So, with this, you can do some conditional logic using CFIF
and the like.
Good luck.
Mikey.