var whitespace = " \t\n\r";
// Check whether string s is empty.
function isEmpty(s)
{   return ((s == null) || (s.length == 0))
}



// Returns true if string s is empty or 
// whitespace characters only.
function isWhitespace (s)

{   var i;

    // Is s empty?
    if (isEmpty(s)) return true;

    // Search through string's characters one by one
    // until we find a non-whitespace character.
    // When we do, return false; if we don't, return true.

    for (i = 0; i < s.length; i++)
    {   
        // Check that current character isn't whitespace.
        var c = s.charAt(i);

        if (whitespace.indexOf(c) == -1) return false;
    }

    // All characters are whitespace.
    return true;
}

function validateForm (form) {
  for (var e = 0; e < form.elements.length; e++) {
    var el = form.elements[e];
    if (el.type == 'text' || el.type == 'textarea' ||
        el.type == 'password' || el.type == 'file' ) { 
      if (isWhitespace(el.value) && el.id != 'optional') {
        alert('Please fill out the text field ' + el.name);
        el.focus();
        return false;
      }
    }
    else if (el.type.indexOf('select') != -1) {
      if (el.selectedIndex <=0) {
        alert('Please select a value of the select field ' + el.name);
        el.focus();
        return false;
      }
    }
    else if (el.type == 'radio') {
      var group = form[el.name];
      var checked = false;
      if (!group.length)
        checked = el.checked;
      else
        for (var r = 0; r < group.length; r++)
          if ((checked = group[r].checked))
            break;
      if (!checked) {
        alert('Please check one of the radio buttons ' + el.name);
        el.focus();
        return false;
      }
    }
    else if (el.type == 'checkbox') {
      var group = form[el.name];
      if (group.length) {
        var checked = false;
        for (var r = 0; r < group.length; r++)
          if ((checked = group[r].checked))
            break;
        if (!checked) {
          alert('Please check one of the checkboxes ' + el.name);
          el.focus();
          return false;
        }
      }
    }
  }
  return true;
}