Has the problem been solved correctly?

Question

JavaScript

Hey! Cantor has a problem The sum of an arbitrary number of brackets , I modified it to work with an unknown number of arguments. Example Is it ok? And it is still not clear why if instead alertof replacing with console.logit no longer works!
I suspect the reason is in the methodtoString

Answer 1

toString should return a string, in the example a number
f.toString = () => currentSum + '';