Calculate the missing Fibonacci numbers in order to predict where that murderer is gonna strike next!

Coding Kata

<script type="text/javascript">
   var runlimit = 12;
   var num1=0, num2=1, ans;
   function getNextFib(){
      ans = (num1 + num2);
      num1 = num2;
      num2 = ans;
      return ans;
   }
   function isPrime(num){
      for(x = num-1; x > 1; x--){
         if(ans % i == 0)
            return false;
         }
         return true;
      }
      for(i = 0; i < runlimit; i++){
         var x = getNextFib();
         document.write(x);
         if(isPrime(x))
            document.write(" is prime!");
            document.write("<br>");
        }
   }
</script>