prime numbers javascript

// 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;
}function test_prime(n){
  if (n===1) {
    return false;
  }else if(n === 2){
    return true;
  }else{
    for(var x = 2; x < n; x++){
      if(n % x === 0){
        return false;
      }
    }
    return true;  
  }
}

console.log(test_prime(37));

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