Funzione chatHeartbeat non viene richiamata

[ANTAGONIA]

Buon giorno a tutti.
Ho scaricato e installato una chat in php, ho qualche problemino, ma partiamo dal primo.
Non capisco come richiamare la funzione chatHeartbeat

//pagina lista-utenti-online.php

//richiamo i file js
<script type="text/javascript" src="jquerychat/js/jquery.js"></script>
<script type="text/javascript" async="true" src="jquerychat/js/chat.js"></script>

//eseguo una query per tirare fuori gli utenti online e genero tanti link con il nominativo per richiamare la funzione chatWith() come qui sotto.

echo "<a href='javascript:void(0)' onclick=\"javascript:chatWith('".$row['cal_firstname']. "','".$_SESSION['webcal_firstname']."')\">".$row['cal_firstname']."</a>"; 

Il link con la funzione chatWith() va a richiamare la medesima funzione in chat.js
Poi c'è un file chat.js dove all'interno c'è questa funzione:

function chatHeartbeat(){
    alert("chatHeartbeat");
    var itemsfound = 0;
    
    if (windowFocus == false) {
 
        var blinkNumber = 0;
        var titleChanged = 0;
        for (x in newMessagesWin) {
            if (newMessagesWin[x] == true) {
                ++blinkNumber;
                if (blinkNumber >= blinkOrder) {
                    document.title = x+' says...';
                    titleChanged = 1;
                    break;    
                }
            }
        }
        
        if (titleChanged == 0) {
            document.title = originalTitle;
            blinkOrder = 0;
        } else {
            ++blinkOrder;
        }


    } else {
        for (x in newMessagesWin) {
            newMessagesWin[x] = false;
        }
    }


    for (x in newMessages) {
        if (newMessages[x] == true) {
            if (chatboxFocus[x] == false) {
                //FIXME: add toggle all or none policy, otherwise it looks funny
                $('#chatbox_'+x+' .chatboxhead').toggleClass('chatboxblink');
            }
        }
    }
    
    $.ajax({
      url: "jquerychat/chat.php?action=chatheartbeat",
      cache: false,
      dataType: "json",
      success: function(data) {


        $.each(data.items, function(i,item){
            if (item)    { // fix strange ie bug


                chatboxtitle = item.f;


                if ($("#chatbox_"+chatboxtitle).length <= 0) {
                    createChatBox(chatboxtitle);
                }
                if ($("#chatbox_"+chatboxtitle).css('display') == 'none') {
                    $("#chatbox_"+chatboxtitle).css('display','block');
                    restructureChatBoxes();
                }
                
                if (item.s == 1) {
                    item.f = username;
                    //alert("user: " + username);
                }


                if (item.s == 2) {
                    //alert("M: " + item.m);
                    $("#chatbox_"+chatboxtitle+" .chatboxcontent").append('<div class="chatboxmessage"><span class="chatboxinfo">'+item.m+'</span></div>');
                } else {
                    //alert("F: " +item.f);
                    newMessages[chatboxtitle] = true;
                    newMessagesWin[chatboxtitle] = true;
                    $("#chatbox_"+chatboxtitle+" .chatboxcontent").append('<div class="chatboxmessage"><span class="chatboxmessagefrom">'+item.f+':&nbsp;&nbsp;</span><span class="chatboxmessagecontent">'+item.m+'</span></div>');
                }


                $("#chatbox_"+chatboxtitle+" .chatboxcontent").scrollTop($("#chatbox_"+chatboxtitle+" .chatboxcontent")[0].scrollHeight);
                itemsfound += 1;
            }
        });


        chatHeartbeatCount++;


        if (itemsfound > 0) {
            chatHeartbeatTime = minChatHeartbeat;
            chatHeartbeatCount = 1;
        } else if (chatHeartbeatCount >= 10) {
            chatHeartbeatTime *= 2;
            chatHeartbeatCount = 1;
            if (chatHeartbeatTime > maxChatHeartbeat) {
                chatHeartbeatTime = maxChatHeartbeat;
            }
        }
        
        setTimeout('chatHeartbeat();',chatHeartbeatTime);
    }});
}

La stessa funzione richiama la pagina chat.php per eseguire una select, che PRESUMO va a ripescare la conversazione tra i due utenti che si stanno parlando oppure che si sono parlati.

//Questo è il file chat.php, qui ci sono una serie di operazioni per dialogare con il DB

<?php
define ('DBPATH','localhost');
define ('DBUSER','root');
define ('DBPASS','');
define ('DBNAME','Sql563051_1');
session_start();
global $dbh;
$dbh = mysql_connect(DBPATH,DBUSER,DBPASS) or die ("Not connect". mysql_error());
mysql_select_db(DBNAME,$dbh);

if ($_GET['action'] == "chatheartbeat") { chatHeartbeat(); } //<-- attraverso questo evento dovrebbe richiamarmi la funzione chatHeartbeat()if ($_GET['action'] == "sendchat") { 
sendChat(); } if ($_GET['action'] == "closechat") { closeChat(); } 
if ($_GET['action'] == "startchatsession") { startChatSession(); } 

if (!isset($_SESSION['chatHistory'])) {    
$_SESSION['chatHistory'] = array();    
}
if (!isset($_SESSION['openChatBoxes'])) {    
$_SESSION['openChatBoxes'] = array();    
}
function chatHeartbeat() {        
$sql = "select * from chat where (chat.id_user=".$_SESSION['id_user']." AND chat.to = '".mysql_real_escape_string($_SESSION['username'])."' AND recd = 0) order by id ASC";   
$query = mysql_query($sql);    
$items = '';
    
$chatBoxes = array();
    
while ($chat = mysql_fetch_array($query)) {
        if (!isset($_SESSION['openChatBoxes'][$chat['from']]) && isset($_SESSION['chatHistory'][$chat['from']])) {            
$items = $_SESSION['chatHistory'][$chat['from']];        
}
        
$chat['message'] = sanitize($chat['message']);
        
$items .= <<<EOD                       
{            
"s": "0",            
"f": "{$chat['from']}",            
"m": "{$chat['message']}"       
}
,EOD;
   
 if (!isset($_SESSION['chatHistory'][$chat['from']])) {        
$_SESSION['chatHistory'][$chat['from']] = '';    
}
    
$_SESSION['chatHistory'][$chat['from']] .= <<<EOD                          
 {            
"s": "0",            
"f": "{$chat['from']}",            
"m": "{$chat['message']}"       
}
,EOD;                

unset($_SESSION['tsChatBoxes'][$chat['from']]);        
$_SESSION['openChatBoxes'][$chat['from']] = $chat['sent'];    
}
    
if (!empty($_SESSION['openChatBoxes'])) {    
foreach ($_SESSION['openChatBoxes'] as $chatbox => $time) {        
if (!isset($_SESSION['tsChatBoxes'][$chatbox])) {            
$now = time()-strtotime($time);            
$time = date('g:iA M dS', strtotime($time));
            
$message = "Sent at $time";           

if ($now > 180) {                
$items .= <<<EOD{
"s": "2",
"f": "$chatbox",
"m": "{$message}"}

,EOD;
    
if (!isset($_SESSION['chatHistory'][$chatbox])) {        
$_SESSION['chatHistory'][$chatbox] = '';    
}
    
$_SESSION['chatHistory'][$chatbox] .= <<<EOD        
{
"s": "2",
"f": "$chatbox",
"m": "{$message}"
}
,EOD;            
$_SESSION['tsChatBoxes'][$chatbox] = 1;        
}        
}    
}
}
    
$sql = "update chat set recd = 1 where chat.id_user=".$_SESSION['id_user']." AND chat.to = '".mysql_real_escape_string($_SESSION['username'])."' and recd = 0";    
$query = mysql_query($sql);
    
if ($items != '') {        
$items = substr($items, 0, -1);    
}
header('Content-type: application/json');?>
{        
"items": [            <?php echo $items;?>        ]
}
<?php            
exit(0);
}
function chatBoxSession($chatbox) {        
$items = '';        
if (isset($_SESSION['chatHistory'][$chatbox])) {        
$items = $_SESSION['chatHistory'][$chatbox];    
}
    
return $items;
}
function startChatSession() {    
$items = '';    
if (!empty($_SESSION['openChatBoxes'])) {        
foreach ($_SESSION['openChatBoxes'] as $chatbox => $void) {            
$items .= chatBoxSession($chatbox);        
}    
}

 if ($items != '') {        
$items = substr($items, 0, -1);    
}
header('Content-type: application/json');?>
{        
"username": "<?php echo $_SESSION['username'];?>",        "items": [            <?php echo $items;?>        ]}
<?php    exit(0);}
function sendChat() {    //$from = $_SESSION['username'];    $from = $_SESSION['webcal_firstname'];    $to = $_POST['to'];    $message = $_POST['message'];
    $_SESSION['openChatBoxes'][$_POST['to']] = date('Y-m-d H:i:s', time());        $messagesan = sanitize($message);
    if (!isset($_SESSION['chatHistory'][$_POST['to']])) {        $_SESSION['chatHistory'][$_POST['to']] = '';    }
    $_SESSION['chatHistory'][$_POST['to']] .= <<<EOD                       {            "s": "1",            "f": "{$to}",            "m": "{$messagesan}"       },EOD;

    unset($_SESSION['tsChatBoxes'][$_POST['to']]);
    $sql = "insert into chat (chat.id_user,chat.from,chat.to,message,sent) values (".$_SESSION['id_user'].",'".mysql_real_escape_string($from)."', '".mysql_real_escape_string($to)."','".mysql_real_escape_string($message)."',NOW())";            $query = mysql_query($sql);    echo "1";    exit(0);}
function closeChat() {
    unset($_SESSION['openChatBoxes'][$_POST['chatbox']]);        echo "1";    exit(0);}
function sanitize($text) {    $text = htmlspecialchars($text, ENT_QUOTES);    $text = str_replace("\n\r","\n",$text);    $text = str_replace("\r\n","\n",$text);    $text = str_replace("\n","<br>",$text);    return $text;}?>

Domanda: come faccio a richiamare la funzione chatHeartbeat ?
Grazie mille.