I am not able to verify that Virtualmin will automatically detect that JavaScript is not available and function correctly. (Some of the advertising copy seems to make this claim.)
I switched off JavaScript in Opera, then went to the demo site at http://virtualmin-demo.virtualmin.com/ and logged in as the demo user "demodomain" with password "demo".
Many of the links are nonfunctional. The JavaScript menus activated by clicking on the + sign at the left margin are nonfunctional. The following items seem to be links, as judged by the cursor shape, but clicking on them causes no effect:
Server Configuration
Backup and Restore
Services
Logs and Reports
Webmin Modules
Rahul