Woowww hooww hold on, why the best its O(n^2)

i think so yes

This is great!

you can use '_' instead, it just a placeholder

od

reducer can take up to 4 arguments, you can just omit the last two, which are indices and array. So you can use acc and value of the index.

its just because without it, the functions assumes W is the index and the last parameter is left off. The functions isnt aware of the parameter name, just the location of the parameter within the callback.

very clever, but by far the slowest I've seen in terms of performance

Generally one can find good and interesting solutions among the top voted ones, but it is not necessary the case of the best voted one.

I suggest you follow multiple highly skilled coders (like akar-0) and instead compare your solutions to them.