"isPrime" implementation is wrong

[Stanko]

Hello,
Thanks for putting this together, I was just browsing and noticed a bug in implementation of isPrime. It returns wrong results.

Try:

isPrime(9); // -> true
isPrime(21); // -> true
isPrime(25); // -> true

And none of these is prime. It will return true for any odd number, as you are skipping all of the odd number dividers (counter has a value of 2 + (n * 2)) on the line #17

  for (let i = 2; i < Math.ceil(Math.sqrt(n)); i += 2) {
    if (n % i === 0) {
      return false
    }
  }

You just need to increment by 1 not by 2.

Cheers!

[bcherny]

Good catch - thanks @Stanko.