fibonacci.js

<script type="text/javascript">
  function fib(num1, num2){
    var sum=num1 + num2;
    
    if (sum > upper){
      return;
    }
    else{
      document.write("<br />" + sum);
      fib(num2, sum);
    }
  }
  
  var upper = prompt("compute fibonacci until ...","20");
  
  if (!new RegExp("^\\d+$").test(upper)){
    document.write("give me a number. you gave me \\" + upper + "\\");
  }
  else if (upper < 1) {
    document.write("nothing to do here, must be a natural number greater than zero");
  }
  else{
    document.write("1<br />1");
    
    if (upper != "1")
      fib(1,1);
  }
</script>