function isEmpty(s)
{
  var whitespace = " \t\n\r";
  var i;
  if((s == null) || (s.length == 0))
    return true;
  // Search string looking for characters that are not whitespace
   for (i = 0; i < s.length; i++)
   {   
       var c = s.charAt(i);
       if (whitespace.indexOf(c) == -1) 
             return false;
   }
  // All characters are whitespace.
  return true;
}
   
function isDigit(c)
{   
  return ((c >= "0") && (c <= "9"))
}
   
function isInteger(field)
{ 
  var i, c;
  var s = field.value;
  if (isEmpty(s))
   {
       alert(field.id + " cannot be empty");
       field.focus(); 
       return false;
   }
 for (i = 0; i < s.length; i++)
  {   // Check if current character is number.
       c = s.charAt(i);
       if (!isDigit(c)) 
        {
          alert(field.id + " must contain only digits");
          field.focus();
          return false;
        }
  }
 
 return true;
}

function isEmptyInteger(field)
{ 
  var i, c;
  var s = field.value;
  if (isEmpty(s))
   {
       return true;
   }
 for (i = 0; i < s.length; i++)
  {   // Check if current character is number.
       c = s.charAt(i);
       if (!isDigit(c)) 
        {
          alert(field.id + " must contain only digits");
          field.focus();
          return false;
        }
  }
 
 return true;
}