That is a problem of emulating functional behavior in a language that is not functional at its core.
In functional languages you mostly don't debug, you reconstruct your functions in a controlled environment while you look at the intermediate results. That works everywhere except on a tiny effectfull portion of your code, where you have to actually debug like the imperative code that it is. In Javascript that effectfull portion is usually all the code, and even the places that could be reconstructed at will you will have to debug first to be sure they haven't side effects.
Funny that you mention this, because part of the problem was that someone had made a fully functional wrapper around the component. Someone else made a second class wrapper around the functional one because the component has text so state is needed. I wrote out the functional wrapper entirely and kept maybe one of the functions in the class wrapper
Now I think a great many things can be made functional in JavaScript, but purists ruin this for everyone else.
In functional languages you mostly don't debug, you reconstruct your functions in a controlled environment while you look at the intermediate results. That works everywhere except on a tiny effectfull portion of your code, where you have to actually debug like the imperative code that it is. In Javascript that effectfull portion is usually all the code, and even the places that could be reconstructed at will you will have to debug first to be sure they haven't side effects.