function checkEmail(s)
{
 var a = false;
 var res = false;
 if(typeof(RegExp) == 'function')
 {
  var b = new RegExp('abc');
  if(b.test('abc') == true){a = true;}
  }

 if(a == true)
 {
  reg = new RegExp('^([a-zA-Z0-9\\-\\.\\_]+)'+
                   '(\\@)([a-zA-Z0-9\\-\\.]+)'+
                   '(\\.)([a-zA-Z]{2,4})$');
  res = (reg.test(s));
 }
 else
 {
  res = (s.search('@') >= 1 &&
         s.lastIndexOf('.') > s.search('@') &&
         s.lastIndexOf('.') >= s.length-5)
 }
 return(res);
}


function checkForm() {
 if(document.getElementById("name").value!="" && document.getElementById("email").value!="" && document.getElementById("fon").value!="") {
  if(checkEmail(document.getElementById("email").value)) {
   return true;
  }
  else {
   alert("Please include your valid email address.");
   return false;
  }
 }
 else {
  alert("Please include your valid name, email address and telephone number!");
  return false;
 }
}