Number Format in JavaScript

<script type="text/javascript" language="javascript">
<!-- //
function Calculate(){

    var entry;
    var first;
    var second;
    var numPlaces;
    first = Number(1);
    second = Number(3);
    numPlaces = Number(2);
    var n = first / second;

    document.write(n+"  vs  "+formatNumber(n,numPlaces));
}

function formatNumber(theNum, numDecPlaces)
{
     var num = new String();
     num = "" + theNum;
     var pos = 0;
     count = 0;
     while (num.substring(pos-1,pos)!== ".") {
       pos += 1 ;
       count += 1;
     }
     while (pos < (count+numDecPlaces)){
       pos +=1;
     }
     return num.substring(0,pos);
}
// -->
</script>