It would make more sense to escape all submitted html instead of trying to sanitise it, also add a sensible character limit. At the moment this guestbook seems to be unusable.

I'd also like to note that doing purification on the client on submit [0] isn't wise - anyone can just skip purification and post something malicious directly to the netlify function. If you absolutely have to sanitisation on the client - at least do it on render instead.

[0] https://github.com/sgolovine/sunnygolovine.com/blob/master/s...