This basically means "Give me an array of letters from sorted input array's first item" ;)

You need to wrap those values with brackets [], because what you posted isn't an array. Using "3 dots" on a string returns an array of characters.

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

i don't understand why the three dots (...), return us an array and not something like this :
"paolo","zarate","azorsa","daniel".
i replaced the ...s with those values: "paolo","zarate","azorsa","daniel", to see what is going on, but i gives me an error.

No problem, I revisited my first solution and it mutated the input too ;). Refactored it to make it pure now.

Lol you just edited your comment as the time I write the reply ^^

In French we say "Les grands esprits se rencontrent".

Should be upvoted best practice as it does not mutate the input.

I liked so much this kata :)