prime or not in javascript code example

Example 1: javascript find a prime number

// This seems to be the most common and comprehensive means
// of implementing a 'is a number a prime function' in javascript 
// if you would like t0 learn more complex , but efficient algorithms. 
// Visit the link below
// https://stackoverflow.com/questions/11966520/how-to-find-prime-numbers-between-0-100

function isPrime(num) {
  if(num < 2) return false;

  for (let k = 2; k < num; k++){
    if( num % k == 0){
      return false;
    }
  }
  return true;
}

Example 2: prime numbers javascript

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

Example 3: prime or not in javascript

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