30-seconds-of-code/snippets/isPrime.md

isPrime

Checks if the provided integer is a prime number.

Check numbers from 2 to the square root of the given number. Return false if any of them divides the given number, else return true, unless the number is less than 2.

const isPrime = num => {
  const boundary = Math.floor(Math.sqrt(num));
  for (var i = 2; i * i <= boundary; i++) if (num % i == 0) return false;
  return num >= 2;
};

isPrime(11) // true
isPrime(12) // false