You can achieve the same goal, if not so elegantly, if you define a node process that processes HTTP POSTs by evaling the body of the request to replace the previous handling function. In practice you'd quickly want to post a function that behaves normally. However you could also define a function that does something "normal" but has a code path for continually redefining the function.

As exotic as this sounds, this is very similar to what web-browsers do with script src tags, especially from 3rd parties. The page is saying "Hey let me eval a function that can do whatever it wants in this context. I trust you!" Most webdevs don't consider this a threat vector!