> This is really basic programming

No, it's not. React is iterating that piece of code of your function internally to modify the value of the const, there is no other way to do it. And it is especially confusing because you can use that const 'variable' in the scope representing a changing value. And the change is magically made by its 'setState' method.

If you do this yourself in a loop then it is of course totally clear what's going on, but now we're writing functions where parts of it are being iterated by React, and that's not functional at all, IMAO it's a hack.