PHP阻止表單重複提交

session_start();

?>

<form method="POST">
    <input type="text" name="countSubmit" value="1">
    <input type="submit" value="submit">
</form>

<?php
if (count($_POST) > 0){
    // 判斷是否重複提交
    if (isset($_SESSION['submited']) && $_SESSION['submited'] === true){
        echo '表單重複提交<br>';
    }else {
        $_SESSION['submited'] = true;
    }
}

?>