Ajax seems to kill IE

[Technocrat]

I have a simple 2 way ajax chat system. Basically it's to allow someone to have 1 on 1 conversations with multiple people. It works fine in FF and Opera but for some reason in IE after a period of time, about 20-30 minutes, IE will stop loading the page. You can't even browse to the page any more. The only way to fix the issue is to restart IE.

I can't figure out why. It's like the pipe I make to the server do not close and keep recreating themselves over and over until IE fails.

var updateInterval = 1000;
var users_content;
var chat_text;
var chat_content;
var buttons;
var xmlHttpGetUsers = createXmlHttpRequestObject();
var xmlHttpGetChats = createXmlHttpRequestObject();
var xmlHttpGetButtons = createXmlHttpRequestObject();
var xmlHttpGetSendMessage = createXmlHttpRequestObject();
var timer_chats;
var isDown = false;

function createXmlHttpRequestObject() {
    // will store the reference to the XMLHttpRequest object
    var xmlHttp;
    // this should work for all browsers except IE6 and older
    try {
        // try to create XMLHttpRequest object
        xmlHttp = new XMLHttpRequest();
    } catch(e) {
        // assume IE6 or older
        var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
                                        "MSXML2.XMLHTTP.5.0",
                                        "MSXML2.XMLHTTP.4.0",
                                        "MSXML2.XMLHTTP.3.0",
                                        "MSXML2.XMLHTTP",
                                        "Microsoft.XMLHTTP");
        // try every prog id until one works
        for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++) {
            try {
                // try to create XMLHttpRequest object
                xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
            } catch (e) {}
        }
    }
    // return the created object or display an error message
    if (!xmlHttp) {
        alert("Error creating the XMLHttpRequest object.");
    } else {
        return xmlHttp;
    }
}

/*=== Users ====*/
function requestUsers() {
    //Random number of IE
    var ran_number = Math.random()*5;
    //URL to go to
    var url = 'get_users.php?my='+my+'&type='+u_type+'&get_users=1&trash='+ran_number;

    if(xmlHttpGetUsers) {
        try {
            // don't start another server operation if such an operation
            // is already in progress
            if (xmlHttpGetUsers.readyState == 4 || xmlHttpGetUsers.readyState == 0) {
                // call the server page to execute the server-side operation
                xmlHttpGetUsers.open("GET", url, true);
                xmlHttpGetUsers.onreadystatechange = handleReceivingUsers;
                xmlHttpGetUsers.send(null);
            } else {
                // we will check again for new users
                setTimeout("requestUsers();", updateInterval);
            }
        } catch(e) {
            displayError(e.toString());
        }
    }
}

function handleReceivingUsers() {
    // continue if the process is completed
    if (xmlHttpGetUsers.readyState == 4) {
        // continue only if HTTP status is "OK"
        if (xmlHttpGetUsers.status == 200) {
            try {
                // process the server's response
                readUsers();
            } catch(e) {
                // display the error message
                displayError(e.toString());
            }
        } else {
            // display the error message
            displayError(xmlHttpGetUsers.statusText);
        }
    }
}

function readUsers() {
    // retrieve the server's response
    var response = xmlHttpGetUsers.responseText;
    //Clear the users
    users_content.innerHTML = '';

    //If there is an error
    if (response.indexOf("ERRNO") >= 0 || response.indexOf("error:") >= 0 ) displayError('Sever Error '+response);
    //If there is no data
    if (response.length == 0) {
        setTimeout("requestUsers();", updateInterval);
        return;
    }

    //Set the users HTML to the response
    users_content.innerHTML = response;
    //Reset the timer
    setTimeout("requestUsers();", updateInterval);
}

/*=== Chats ===*/
function requestChats() {
    //Random number of IE
    var ran_number = Math.random()*5;
    //URL to go to
    var url = 'chat.php?last_chat='+last_chat+'&sid='+chat_id+'&type='+u_type+'&my='+my+'&trash='+ran_number;

    if(xmlHttpGetChats) {
        try {
            // don't start another server operation if such an operation
            // is already in progress
            if (xmlHttpGetChats.readyState == 4 || xmlHttpGetChats.readyState == 0) {
                // call the server page to execute the server-side operation
                xmlHttpGetChats.open("GET", url, true);
                xmlHttpGetChats.onreadystatechange = handleReceivingChats;
                xmlHttpGetChats.send(null);
            } else {
                // we will check again for new messages
                timer_chats = setTimeout("requestChats();", updateInterval);
            }
        } catch(e) {
            displayError(e.toString());
        }
    }
}

function handleReceivingChats() {
    // continue if the process is completed
    if (xmlHttpGetChats.readyState == 4) {
        // continue only if HTTP status is "OK"
        if (xmlHttpGetChats.status == 200) {
            try {
                // process the server's response
                readChats();
            } catch(e) {
                // display the error message
                displayError(e.toString());
            }
        } else {
            // display the error message
            displayError(xmlHttpGetChats.statusText);
        }
    }
}

function readChats() {
    // retrieve the server's response
    var response = xmlHttpGetChats.responseText;

    //Split the response
    var ret = new Array(2);
    ret = get_last_chat(response);
    response = ret[0];
    last_chat = ret[1];

    if (response.indexOf("ERRNO") >= 0 || response.indexOf("error:") >= 0 ) displayError('Sever Error '+response);
    if (response.length <= 1) {
        timer_chats = setTimeout("requestChats();", updateInterval);
        return;
    }

    chat_content.innerHTML = chat_content.innerHTML + response;
    chat_content.scrollTop = chat_content.scrollHeight;
    timer_chats = setTimeout("requestChats();", updateInterval);
}

/*=== Send Chat ===*/
function send_chat_text() {
    //Random number of IE
    var ran_number = Math.random()*5;
    //URL to go to
    //We encode it in base 64 just to make sure that nothing gets lost in translation
    var url = 'chat.php?my='+my+'&type='+u_type+'&text='+ encode(chat_text.value) +'&chat_id=' +chat_id+'&trash='+ran_number;

    //Clear the text area
    chat_text.value ='';
    chat_text.focus();
    //Send the command
    if(xmlHttpGetSendMessage) {
        try {
            // don't start another server operation if such an operation
            // is already in progress
            if (xmlHttpGetSendMessage.readyState == 4 || xmlHttpGetSendMessage.readyState == 0) {
                // call the server page to execute the server-side operation
                xmlHttpGetSendMessage.open("GET", url, true);
                xmlHttpGetSendMessage.send(null);
            }
        } catch(e) {
            displayError(e.toString());
        }
    }
}

/*=== Buttons ===*/
function requestButtons() {
    var ran_number = Math.random()*10;
    var url = 'get_buttons.php?sid='+chat_id+'&my='+my+'&type='+u_type+'&trash='+ran_number;

    // only continue if xmlHttpGetMessages isn't void
    if(xmlHttpGetButtons) {
        try {
            // don't start another server operation if such an operation
            // is already in progress
            if (xmlHttpGetButtons.readyState == 4 || xmlHttpGetButtons.readyState == 0) {
                // call the server page to execute the server-side operation
                xmlHttpGetButtons.open("GET", url, true);
                xmlHttpGetButtons.onreadystatechange = handleReceivingButtons;
                xmlHttpGetButtons.send(null);
            }
        } catch(e) {
            displayError(e.toString());
        }
    }
}

function handleReceivingButtons() {
    // continue if the process is completed
    if (xmlHttpGetButtons.readyState == 4) {
        // continue only if HTTP status is "OK"
        if (xmlHttpGetButtons.status == 200) {
            try {
                // process the server's response
                readButtons();
            } catch(e) {
                // display the error message
                displayError(e.toString());
            }
        } else {
            // display the error message
            displayError(xmlHttpGetButtons.statusText);
        }
    }
}

function readButtons() {
    // retrieve the server's response
    var response = xmlHttpGetButtons.responseText;

    if (response.indexOf("ERRNO") >= 0 || response.indexOf("error:") >= 0 ) displayError('Sever Error '+response);
    if (response.length == 0) {
        return;
    }

    buttons.innerHTML = response;
}

/*=== Other Functions ===*/

// function that displays an error message
function displayError(message) {
    alert("Error accessing the server! "+ "\r\n" + message);
}

function get_last_chat(Request) {
    var ret = new Array(2);
    loc = Request.indexOf('<last_chat>');
    loc2 = Request.indexOf('</last_chat>');
    if ((loc-1) <= 0) {
        ret[0] = '';
    } else {
        ret[0] = Request.substring(0, loc-1);
    }
    ret[1] = Request.substring(loc+11, loc2);
    return ret;
}

function keydown(e) {
    var characterCode; //literal character code will be stored in this variable
    e = (!e) ? window.event : e;

    characterCode = (e.charCode) ? e.charCode :
         ((e.keyCode) ? e.keyCode :
         ((e.which) ? e.which : 0));

    //If Shift
    if (characterCode == 16) {
        isDown = true;
    }
    //If CTRL
    if (characterCode == 17) {
        isDown = true;
    }

}
function checkEnter(e){ //e is event object passed from function invocation
    var characterCode; //literal character code will be stored in this variable
    e = (!e) ? window.event : e;

    characterCode = (e.charCode) ? e.charCode :
         ((e.keyCode) ? e.keyCode :
         ((e.which) ? e.which : 0));

    if(characterCode == 13 && (isDown == null || !isDown)){ //if generated character code is equal to ascii 13 (if enter key)
        send_chat_text(); //submit the form
        return false;
    } else {
        isDown = false;
        return true;
    }
}

function change_chat(chatid) {
    clearTimeout(timer_chats);
    //Add the chat just sent
    chat_content.innerHTML = '';
    //Set focus back to it
    chat_text.focus();
    chat_id = chatid;
    last_chat = 0;
    requestButtons();
    requestChats();
}

function loader() {
    users_content = xGetElementById("users");
    chat_text = xGetElementById("chat_text");
    chat_content = xGetElementById("chat_content");
    buttons = xGetElementById("chat_buttons");
    requestUsers();
    requestChats();
    chat_text.focus();
}

if (window.addEventListener) {
    window.addEventListener("load", loader, false);
} else if (window.attachEvent) {
    window.attachEvent("onload", loader);
}

Any ideas?