Is there a way to obfuscate the codes written in function nodes suppose if I want to deploy my flows to the client side?
The only strong way to hide your code is to put it on your own server and make it available via an API.
here is an online version:
Just note that it most certainly does not "prevent". That is not possible for a scripting language (and almost certainly not for any other either). It just makes it harder. But it also makes the code less efficient.