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.