I doubt that JavaScript can help improve your banning system.
But if what you really want is just scan an html page an check if there are any IP numbers or url that redirects to the IP list,then yes it is possible.
But if the IP banned list is on your website database then no, JavaScript probably can't really access your DB.
Didn't understand the question at all
I work on a site where we tend to get DDOS attacks and people trying to hack accounts. Our server auto bans the IP's but this leads to trouble as they could be using a VPN, and we block regular users.
So what I was wanting to know is it possible for someone to scan an HTML page and then check our ban list and if there is a banned IP Highlight it or place an icon next to it.