function checkMail(e) {
  var str = trim(e);
  var filter=/^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/i
  if (filter.test(str)) return false
  else return true;
}

function checkForm() {
  if(checkMail(document.getElementById('email').value)) {
    alert('Vul a.u.b. een geldig email adres in.');
	return false;
  }
  return true;
}

function trim(str, chars) {
    return ltrim(rtrim(str, chars), chars);
}

function ltrim(str, chars) {
    chars = chars || "\\s";
    return str.replace(new RegExp("^[" + chars + "]+", "g"), "");
}

function rtrim(str, chars) {
    chars = chars || "\\s";
    return str.replace(new RegExp("[" + chars + "]+$", "g"), "");
}