A file with a .jss extension will be run as JSS if:
If these conditions are not satisfied then the file will be served up the same as an non-JSS file.
Note that for JSS web-apps to be available to unauthenticated users, JSS must be enabled for the owner of the /Public folder, i.e. anonymous, which it isn't by default.
For more information on how to host a web-app in CompleteFTP, please refer to.