I'm sure a lot of people would be grateful to you, if you can do this. I, for one, would like it.
However, I don't use java or javascript in my browser, and my Danasoft version works just fine. If you write it in javascript, I imagine that wouldn't work for somebody like myself.
The reason for not using javascript is that even if you are behind a proxy server, and have disabled everything else that might compromise your privacy, if you use javascript your real IP address can still be read. (But you probably know all this.) I don't know all the reasons, but I know from checking my security features that this is true. And since my main purpose for having one of these IP checkers on my blog is to educate people about just how much information they are giving out when they visit web pages, then it is counterproductive if they must enable javascript in order to use it.
I have nothing against javascript, for certain things, at least, but for my ordinary web surfing I use a secure browser. When I visit this site, of course, I use a different browser, and that is okay.
Anyway, I am not sure how they create these IP checkers; maybe they write it using a different script? I tried stealing the code to study it, but every one is different. And also, I have an actual job that tends to get in the way of life, and this computer stuff gets set aside.
Although I don't have a lot of javascript experience I could try to write a script that does this.