function to format a fixed digit number

Hello Folks,
I am using attached function to format some fixed digit number but it is giving me an error.
Please can you see if this is not correct?
thanks
s

<script>
function twoDecimal(num,round) {
  if (round) return num.toFixed(2);
  var stringNum = String(num);
  if (stringNum.indexOf('.')==-1) return stringNum+'.00';
  var newNum = stringNum.split('.');
  if (newNum.len==2) {
    newNum[1]=(newNum[1].length>2)?newNum[1].subString(0,2):newNum[1];
  }
  if (newNum[1].length==1) newnum[1]+="0"
  return newNum[0]+'.'+newNum[1]
}
alert(twoDecimal(133.5999,1));
alert(twoDecimal(133.5999));
alert(twoDecimal(133));
alert(twoDecimal(133.5));
 
</script>

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