Javascript: Left Pad

function leadingZeros(num, totalChars, padWith) 
{
 num = num + "";
 padWith = (padWith) ? padWith : "0";
 if (num.length < totalChars) 
 {
  while (num.length < totalChars) 
  {
   num = padWith + num;
  }
 } 
 else {}

 if (num.length > totalChars) 
 { 
  //if padWith was a multiple character string and num was overpadded
  num = num.substring((num.length - totalChars), totalChars);
 } else {}
 return num;
}