HCF

function gcd(a,b){
   let hcf;
   for (let i = 1; i <= a && i <= b; i++) {

    // check if is factor of both integers
    if( a % i == 0 && b % i == 0) {
        hcf = i;
    }
}
  return hcf;
}
 gcd(6, 15);