Every once in a while somebody says “I want to put an IF-style interface on a web page, it doesn’t have to have a real parser, I just want to write some Javascript code to accept line input and print some output.” And then I say “You should use GlkOte for that!” And then they look at GlkOte, look vaguely confused, and give up and write their own thing.
(Most recent example: “I Palindrome I”. No offense, inky.)
I just put together a GlkOte demo which should be very easy to customize for this sort of task. Copy it, edit the startup() and respond() functions, and install it along with the rest of the GlkOte files (javascripts and CSS).