prime or not in javascript

1// This seems to be the most common and comprehensive means
2// of implementing a 'is a number a prime function' in javascript 
3// if you would like t0 learn more complex , but efficient algorithms. 
4// Visit the link below
5// https://stackoverflow.com/questions/11966520/how-to-find-prime-numbers-between-0-100
6
7function isPrime(num) {
8  if(num < 2) return false;
9
10  for (let k = 2; k < num; k++){
11    if( num % k == 0){
12      return false;
13    }
14  }
15  return true;
16}

1function isPrime(num) {
2    for (let i = 2; i * i <= num; i++)
3        if (num % i === 0)
4          return false; 
5    return num > 1;
6}

1function isPrime(num) {
2  for(var i = 2; i < num; i++)
3    if(num % i === 0) return false;
4  return num > 1;
5}

1function isPrime(num) {
2  for(var i = 2; i < num; i++)
3    if(num % i === 0) return false;
4  return num > 1;
5}
6