如何在php中在同一页面上显示错误消息？

这是我的简单php表单脚本 当前，此脚本在下一页中显示所有错误，但我想在注册页中显示错误我如何才能做到这一点 我在学习php

<?php
// i removed connection code due to mostly code error 
if (mysqli_connect_errno()) {
    exit('Failed to connect to MySQL: ' . mysqli_connect_error());
}
if (empty($_POST['username']) || empty($_POST['account']) || empty($_POST['package']) || empty($_POST['Method']) || empty($_POST['TransactionId'])) {
    exit('Please complete the registration form');
}
if ($stmt = $con->prepare('SELECT id, TransactionId FROM payment WHERE username = ?')) {
    //i removed this code due to this error "It looks like your post is mostly code; please add some more details. if u want this plz let me know"

    } else {
    if ($stmt = $con->prepare('INSERT INTO payment (username, account, package, Method, TransactionId) VALUES (?, ?, ?, ?, ?)')) {
    $stmt->bind_param('sssss', $_POST['username'], $_POST['account'], $_POST['package'], $_POST['Method'], $_POST['TransactionId']);
    $stmt->execute();
    echo 'You have successfully registered, you can now login!';
    } else {
    echo 'Could not prepare statement!';
}
    }
    $stmt->close();
} else {
    echo 'Could not prepare statement!';
}
$con->close();
?>

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要提交表单并在同一页面上显示结果而不重新加载，您需要使用Wesley is right，您需要在后台异步请求来处理PHP页面而不提交。这是用Javascript和AJAX完成的。但是php代码中的错误我如何用Javascript显示感谢您的回复

exit('Please complete the registration form');