var whitespace = " tnr";

function isValidEmail(s) { if (isEmpty(s)) return false;
  if (isWhitespace(s)) return false;

  var i = 1;
  var sLength = s.length;

  while ((i < sLength) && (s.charAt(i) != "@")) { i++ }

  if ((i >= sLength) || (s.charAt(i) != "@")) return false;
  else i += 2;

  while ((i < sLength) && (s.charAt(i) != ".")) { i++ }

  if ((i >= sLength - 1) || (s.charAt(i) != ".")) return false;
  else return true;
};

function isEmpty(s) {
  return ((s == null) || (s.length == 0))
};

function isWhitespace(s) {
  var i;
    if (isEmpty(s)) return true;
    for (i = 0; i < s.length; i++) {
      var c = s.charAt(i);
      if (whitespace.indexOf(c) == -1) return false;
    }

    return true;
};

function checkForm() {
  if (!isValidEmail(document.newsletterSubscription.elements['Email Address'].value)) {
    document.newsletterSubscription.elements['Email Address'].style.backgroundColor='yellow';

    alert("Please enter a valid Email Address. (name@host.com)");

    document.newsletterSubscription.elements['Email Address'].focus();

    return false;
  }
};