Prova questo....

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
</head>
<body>
<script language="JavaScript" type="text/javascript">
<!--
function format2dec(value) {
 a = value * 100;
 a = parseInt(a);
 a = a / 100;
 return a;
} // function format2dec(value)

function dec2Str(value) {
 a = format2dec(value);
 if (a == parseInt(a)) {
  return a+'.00';
 } // if (a == parseInt(a)) 
 if (a * 10 == parseInt(a * 10)) {
  return a+'0';
 } // if (a * 10 == parseInt(a * 10))
 return a;
} // function dec2Str(value)


alert(dec2Str(11));
alert(dec2Str(11.1));
alert(dec2Str(11.12));
alert(dec2Str(11.123));
alert(dec2Str(11.108));
alert(dec2Str(11.008));


//-->
</script>

</body>
</html>