Javascript padding

 function pad(str, character, max, side, visibility) {
  str = str.toString();
  console.log('inside pad: '+str);
  var pad;
  var output;
  pad='';
  for (var i=str.length;i<max;i++ ) {
       pad = pad + character;
  }
  pad="<span style='visibility:"+ visibility + "'>" + pad + "</span>";
  side=='left'?  output=pad+str : output=str+pad ;
  return output;
 }

input=$('#serialnumber').text(); 
$('#serialnumber').html(  pad( input, 'F', 16, 'right', 'hidden')  );