check a number is prime or not in javascript code example

Example 1: Javascript prime number check

// 6k+-1 optimisation
function is_prime (n) {
  if (n < 3) return n > 1;
  else if (n % 2 === 0 || n % 3 === 0) return false;
  else if (n < 25) return true;
  let i = 5;
  while (i * i <= n ) {
    if (n % i === 0 || n % (i + 2) === 0) return false;
    i += 6;
  }
  return true;
}

Example 2: prime or not in javascript

function isPrime(num) {
  for(var i = 2; i < num; i++)
    if(num % i === 0) return false;
  return num > 1;
}