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

That's a great site! Thanks for the link, never heard of it before.

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.

! is a regular character in JS regex, but ? is a special character (the "zero or one" quantifier in this specific instance) which has to be escaped.

/!/g how did it work without scaping like this /?/g

Do you know what a pure function is? Look it up if you don't.
If the solution to this kata were a pure function, it will clearly not work. Therefore...

um i don't understand how??? i have looked at it for a while and i can't figure it out. i mostly d ojava, but javascript is really simiar.

!! is used to convert a truthy/falsy value to its boolean equivalent.

let num = 5; (truthy)
!num // false
!!num // true

let num = 0; (falsy)
!num // true
!!num // false

comparing 5 with !!5 would be the equivalent of comparing 5 with true (which is false)
5 === !!5
5 === true

The only reason people still use it over Boolean (other than wanting to look like elite hackers) is because it's something like 10-15% faster (last time I checked)

Yes there is an issue with the test cases.

They should add a test case like the one you lay out here.

Try that in regex101.com And there is no need to ask the same three times.

What do the brackets [ ] do?

Awesome solution, dude!