then this guy only completed 7 Katas lol. how ironic

Because some people (icluding me) didn't knew about .replace.

It's not bad practice. It's just different approach taking into consideration the performance of the solution.

try to figure it out why paj :D

I think the same can be done like this:
return root%1 ? -1 : Math.pow(++root, 2);

since root%1 would return a non zero value (i.e. it's remainder) if it not completely divisible.

Indeed a clever and cool idea. :)

why use switch/if conditions if Javascript has already functions like .replace(), .split() .map() .join() etc, which can reduce the number of lines you code? Indeed a bad practise.

Wow! I thought competitive programming makes use of less codes. Why don't you StackOverflow to see if such function already exists in JS, which can reduce 96% of the code you wrote? I swear this to be a bad practise.

Thanks for explaining @user4202879

You need not take 2 variable of same identifier s.