Question

我正在阅读“构建响应式Web应用程序AJAX和PHP”一书中的PHP / AJAX聊天教程，我遇到以下错误：

 TypeError: Cannot read property 'documentElement' of null

我很确定它在javascript文件中引用了这段代码：

function readMessages(){
    var response = XmlHttpGetMessage.responseText;

    if(response.indexOf("ERRNO") >= 0 || response.indexOf("error:")>= 0 || response.length==0){
        throw(response.length == 0 ? "Void server response." : response);
    }   

    response = XmlHttpGetMessage.responseXML.documentElement;

    clearChat = response.getElementByTagName("clear").item(0).firstChild.data;

    if(clearChat == "true"){
        $("#scroll").html("");
        lastMessageID = -1;
    }

    idArray = response.getElementByTagName("id");
    //nameArray = response.getElementByTagName("name");
    timeArray = response.getElementByTagName("time");
    messageArray = response.getElementByTagName("message");

    displayMessages(idArray, nameArray, timeArray, messageArray);

    if(idArray.length>0){
        lastMessageID = idArray.item(idArray.length - 1).firstChile.data;
        setTimeout("requestNewMessages();", updateInterval);
    }
}

这是我发送的ajax请求：

if(cache.length>0){
    params = cache.shift();
}else{
    params="mode=RetrieveNew" +
           "$id=" +lastMessageID;
}

XmlHttpGetMessage.open("POST", chatURL, true);
XmlHttpGetMessage.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
XmlHttpGetMessage.onreadystatechange = handleRecievingMessages;
XmlHttpGetMessage.send(params);

这是PHP文件：

<?php
require_once('init.php');


$mode = $_POST['mode'];
id=0;
$chat = new Chat();
if($mode=='SendAndRetrieveNew'){
    $user_id = $_POST['user_id'];
    $message = $_POST['message'];
    $color = $_POST['color'];
    $id = $_POST['id'];

    if($user_id != '' && $message != '' && $color != ''){
        $chat->postNewMessage($user_id, $message, $color);
    }
}elseif($mode=='DeleteAndRetrieveNew'){
    $chat->deleteAllMessages();
}elseif($mode=='RetrieveNew'){
    $id = $_POST['id'];
}

if(ob_get_length()){ob_clean();}

header('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); 
header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . 'GMT'); 
header('Cache-Control: no-cache, must-revalidate'); 
header('Pragma: no-cache');
header('Content-Type: text/xml');

echo $chat->getNewMessages($id);
?>

这是句柄接收消息功能 function handleRecievingMessages（）{

    if(XmlHttpGetMessage.readyState == 4){
        if(XmlHttpGetMessage.status == 200){
                try{

                    readMessages();
                }catch(e){
                    displayError(e.toString());
                }   
            }else{
                displayError(XmlHttpGetMessage.statusText);
            }
        }
    }

最后我的getNewMessages函数

public function getNewMessages($id=0){
            $queryArray = array($id);
             if($id>0){ 
        //only get the new messages
        $query = 
        ' SELECT message_id, user_id, message, DATE_FORMAT(posted_on, "%H:%i:%s") 
        AS posted_on FROM chat WHERE message_id > ' 
        . $id . 
        ' ORDER BY message_id ASC'; 
        }else{
        //on the first load only retrieve the last 50 messages from server
        $query = 
        ' SELECT message_id, user_id, message, posted_on 
        FROM (SELECT message_id, user_id, message,s DATE_FORMAT(posted_on, "%H:%i:%s") 
        AS posted_on FROM chat ORDER BY message_id DESC LIMIT 50) AS Last50 
        ORDER BY message_id ASC';
        } 

            $query = $this->_database->_link->prepare($queryString);
            $query->execute();

            $response = '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>';
        $response .= '<response>';  
        $response .= $this->isTableCleared($id); // output the clear flag

        // if we have any results, loop through all the fetched messages to build the result message
        if($query->rowCount()){ //get number of rows in a result, aka check for results
        while ($row = $query->fetch(PDO::FETCH_ASSOC)){ //get results as an associative array
        $id = $row['message_id'];
        $userName = $row['user_id'];
        $time = $row['posted_on'];
        $message = $row['message'];
        $response .= '<id>' . $id . '</id>' . 
                     '<color>' . $color . '</color>' . 
                     '<time>' . $time . '</time>' . 
                     '<name>' . $userName . '</name>' . 
                     '<message>' . $message . '</message>';
      }

      $query->close(); // close the database connection
    }
    $response .= '</response>';
    return $response;
        }

当我使用firebug调试时，我得到以下文本响应：

    "<br /> <b>Parse error</b>: syntax error, unexpected ';', expecting T_FUNCTION in `<b>C:\xampp\htdocs\thinkaztech\includes\chat.class.php</b> on line <b>93</b><br /> "`

但是我没有93号线？

我不确定错误是什么，我已经很好地连接到数据库了，我的chat.class.php文件似乎被正确调用了。感谢您提前提供任何有用的建议！

Answer 1

看起来像是一个错字：

params="mode=RetrieveNew" +
       "$id=" +lastMessageID;
        ^ should be a & not a $

TypeError：无法读取null PHP / AJAX聊天的属性'documentElement'

1 个答案: