PHP お問い合わせフォーム

<?php
//error_reporting(-1);
//ini_set('display_errors', 'On');
session_start();

if (isset($_POST["nn"]) && $_POST["token"] == $_SESSION["token"]) {

  $smtp = "";
  $to = "";
  $subject = "件名";
  $message = "名前：" . h($_POST["nn"]);
  $from = "";

  ini_set("SMTP", $smtp);
  ini_set("smtp_port","587");

  mb_language("japanese");
  mb_internal_encoding("UTF-8");
  mb_send_mail($to, $subject, $message, "From:" . $from);

  echo "<script>(function(){alert('送信しました。');}());</script>";

} else {

}

$_SESSION["token"] = md5(mt_rand());

function h($s){
  return htmlspecialchars($s, ENT_QUOTES, "UTF-8");
}

?>

<!DOCTYPE html>
<html lang="ja">
<head>
  <meta charset="UTF-8">
  <title>お問い合わせテスト</title>
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
</head>
<body>

<form action="" method="post" id="ff">
名前：<input type="text" name="nn" id="nn">
<input type="submit" value="送信">
<input type="hidden" name="token" value="<?php echo $_SESSION["token"]; ?>">
</form>

<script>

$("#ff").submit(function(){
  
  if($("#nn").val() == ""){
    alert("名前の入力は必須です。")
    return false;
  }

  return true;

});

</script>

</body>
</html>

<?php

//error_reporting(-1);

//ini_set('display_errors', 'On');

session_start();

if (isset($_POST["nn"]) && $_POST["token"] == $_SESSION["token"]) {

$smtp = "";

$to = "";

$subject = "件名";

$message = "名前：" . h($_POST["nn"]);

$from = "";

ini_set("SMTP", $smtp);

ini_set("smtp_port","587");

mb_language("japanese");

mb_internal_encoding("UTF-8");

mb_send_mail($to, $subject, $message, "From:" . $from);

echo "<script>(function(){alert('送信しました。');}());</script>";

} else {

}

$_SESSION["token"] = md5(mt_rand());

function h($s){

return htmlspecialchars($s, ENT_QUOTES, "UTF-8");

}

<!DOCTYPE html>

<head>

<title>お問い合わせテスト</title>

</head>

<body>

名前：<input type="text" name="nn" id="nn">

</form>

$("#ff").submit(function(){

if($("#nn").val() == ""){

alert("名前の入力は必須です。")

return false;

}

return true;

});

</script>

</body>

</html>