This is quite absurd.
2. If you don't know reduce or reduceRight, there's a low chance that you are a practical, experienced developer.
3.const [, , foo] = parts and const [foo] = parts are just different. The first expression gets the third element from the array, while the second expression gets the first element out of the array. I am lost as to your intention on what you are trying to say here.
4. I stopped reading then.