Hi
Sounds like you want to develop an automation script! The best way to start IMHO is to read the book "Automating Junos Administration" (recently published)
http://shop.oreilly.com/product/0636920041498.do
I recommend starting with developing a CLI script. Once it works, you can build some sort of web front-end to it. However this will not be a page on SRX, but on a separate server (most probably Linux machine).
P.S. I don't know what existing page are you referring to.