function validate(form) {
  var ok = true;
  var error = "Please correct the following errors:\n";


  if (form.email.value.length == 0 || isValidAddress(form.email.value) == false) {
    error += "You have not supplied a correct e-mail address.\n"; 
    ok = false;
  }

  if (form.name.value.length == 0) {
    error += "You have not filled out the 'Name' field.\n"; 
    ok = false;
  }

  if (form.subject.value.length == 0) {
    error += "You have not filled out the 'Subject' field.\n";
    ok = false;
  }

  if (form.message.value.length == 0) {
    error += "You have not filled out the 'Message' field.\n";
    ok = false;
  }

  if (!ok) {
    alert(error);
  }

  return ok;
}

function isValidAddress( address ) {
	// define search pattern
	var pattern = /^[A-Za-z0-9._%-]+@[A-Za-z0-9._%-]+\.[A-Za-z0-9._%-]{2,4}$/; 
	
	// search and return result
	if (address.match(pattern) ) {
	  return true;
	} else {
	  return false;
	}
}