我使用 Ajax 進行的 PHP 用戶名驗證在 html div（這是為了顯示 ajax 錯誤）元素中復制了我的 html 頁面。我嘗試了一些解決方案并用谷歌搜索，但找不到其他解決方案。也許問題出在 $_POST 但我也在 php 中將它們分開（所有輸入驗證）。這是PHP代碼<?php if(isset($_POST['username'])){    //username validation    $username = $_POST['username'];    if (! $user->isValidUsername($username)){        $infoun[] = 'Your username has at least 6 alphanumeric characters';    } else {        $stmt = $db->prepare('SELECT username FROM members WHERE username = :username');        $stmt->execute(array(':username' => $username));        $row = $stmt->fetch(PDO::FETCH_ASSOC);        if (! empty($row['username'])){            $errorun[] = 'This username is already in use';        }    }}if(isset($_POST['fullname'])){    //fullname validation    $fullname = $_POST['fullname'];    if (! $user->isValidFullname($fullname)){        $infofn[] = 'Your name must be alphabetical characters';    }   }if(isset($_POST['password'])){    if (strlen($_POST['password']) < 6){        $warningpw[] = 'Your password must be at least 6 characters long';    }   }if(isset($_POST['email'])){    //email validation    $email = htmlspecialchars_decode($_POST['email'], ENT_QUOTES);    if (! filter_var($email, FILTER_VALIDATE_EMAIL)){        $warningm[] = 'Please enter a valid email address';    } else {        $stmt = $db->prepare('SELECT email FROM members WHERE email = :email');        $stmt->execute(array(':email' => $email));        $row = $stmt->fetch(PDO::FETCH_ASSOC);        if (! empty($row['email'])){            $errorm[] = 'This email is already in use';        }    }}?>這是屏幕截圖：