Php 从AJAX响应中获取一个未定义的html

(对拼写错误的单词表示歉意) 大家好，大家好 希望你玩得开心. 我是第一次使用AJAX，并试图通过AJAX将一些元素(发送和接收的消息)添加到html中，但我唯一得到的是一个未定义的html文本.

messageInsert和第一次访问正常，但从get_msg我得到一个sql语法错误:

致命错误:未捕获MySQLSQL_EXCEPTION:您的SQL语法有错误；请查看与您的MariaDB服务器版本对应的手册，了解正确的语法，以便在C:\xampp\htdocs\project\myProjects\Chatbot\php\get_msg.php:9堆栈跟踪的第1行使用NEAR‘AND INPING_ID=)OR(OUTENT_ID=AND INFING_ID=)ORDER BY MSG_ID DESC’:#0 C:\xampp\htdocs\project\myProjects\Chatbot\php\get_msg.php(9):MYSQLI-&gt；查询(‘SELECT*FROM m...’)#1{Main}在第9行的C:\xampp\htdocs\project\myProjects\Chatbot\php\get_msg.php中抛出

MessageInsert.php:

<?php
    session_start();
    require_once 'connection.php';
    if (isset($_SESSION['userID'])) {
        $outgoing_id = mysqli_real_escape_string(connection() , $_POST['outgoing_id']);
        $incoming_id = mysqli_real_escape_string(connection() , $_POST['incoming_id']);
        $message = mysqli_real_escape_string(connection() , $_POST['message']);
        if (!empty($message)) {
            $query = "INSERT INTO messages (outgoing_id, incoming_id, msg) VALUES ($outgoing_id , $incoming_id , '$message')";
            $result =connection()->query($query);
        }
    }

Get_msg.php:

<?php
    session_start();
    require_once 'connection.php';
    if (isset($_SESSION['userID'])) {
        $outgoing_id = mysqli_real_escape_string(connection() , $_POST['outgoing_id']);
        $incoming_id = mysqli_real_escape_string(connection() , $_POST['incoming_id']);
        $output = "";
        $query = "SELECT * FROM messages WHERE (outgoing_id = {$outgoing_id} AND incoming_id = {$incoming_id}) OR (outgoing_id = {$incoming_id} AND incoming_id = {$outgoing_id}) ORDER BY msg_id DESC";
        $result = connection()->query($query);
        while ($row = mysqli_fetch_assoc($result)) {
            if ($outgoing_id === $row['outgoing_id']) {
                $output ='<div class="message-send my-4">
                               <p>'.$row['msg'].'</p>
                           </div>';
            } else {
                $output = '<div class="message-receive">
                                <img class="message-receive-pic mb-3 me-2" src="style/ProfilePic/'.$_SESSION['userPic'].'" alt="">
                                <div class="message-receive-text-box my-4">
                                    <p> '. $row['msg']  .'</p>
                                </div>
                           </div>';
            }
            echo $output;
        }
    }

我的名字:

let form = document.querySelector(".mySend"),
    sendInput = form.querySelector(".message"),
    sendBtn = form.querySelector(".sendBtn"),
    chatBox = document.querySelector(".chat-box");
form.onsubmit = (e)=> {
    e.preventDefault();
}
sendBtn.onclick = ()=> {
    let xhr = new XMLHttpRequest();
    xhr.open("POST" , "http://localhost/project/myProjects/Chatbot/php/messageInsert.php" , true);
    xhr.onreadystatechange = ()=> {
        if (xhr.readyState === XMLHttpRequest.DONE) {
            if (xhr.status === 200){
                sendInput.value = "";
            }
        }
    }
    let formData = new FormData(form);
    xhr.send(formData);
}
setInterval(()=> {
    let xhr = new XMLHttpRequest();
    let data = "";
    xhr.open("POST" , "php/get_msg.php" , true);
    xhr.onload = ()=> {
        if (xhr.readyState === XMLHttpRequest.DONE) {
            if (xhr.status === 200) {
                data = this.response;
                chatBox.innerHTML = data;
            }
        }
    }
    let formData = new FormData(form);
    xhr.send(formData);
}, 500);

我的html:

<div class="chat-box">

    </div>
    <div class="type-box">
        <form class="mySend" method="post" autocomplete="off">
            <input type="hidden" value="<?php echo $userProfile['id'] ?>" name="incoming_id">
            <input type="hidden" value="<?php echo $_SESSION["profileID"] ?>" name="outgoing_id">
            <input class="message form-control" type="text" placeholder="Type your message here..." name="message">
            <button type="submit" class=" sendBtn btn btn-dark" name="sendBtn"><i class="fab fa-telegram-plane"></i></button>
        </form>
    </div>

我对表名和列名很确定.

非常感谢您的帮助:)

我已经try 了AJAX和php文件中的所有方法，都没有奏效.