check if prime number javascript code example

Example 1: prime numbers javascript

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

Example 2: javascript find prime number

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));

Example 3: 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;
}