Question

This code works in Chrome and Firefox, but not IE (which is to be expected). Does anyone see anything wrong with this code that would render it useless in IE?

var waittime=400;
chatmsg = document.getElementById("chatmsg");
room = document.getElementById("roomid").value; 
sessid = document.getElementById("sessid").value;
chatmsg.focus()
document.getElementById("chatwindow").innerHTML = "loading...";
document.getElementById("userwindow").innerHTML = "Loading User List...";
var xmlhttp = false;
var xmlhttp2 = false;
var xmlhttp3 = false;
function ajax_read() {
if(window.XMLHttpRequest){
    xmlhttp=new XMLHttpRequest();
    if(xmlhttp.overrideMimeType){
        xmlhttp.overrideMimeType('text/xml');
    }
} else if(window.ActiveXObject){
    try{
        xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
        try{
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e){
        }
    }
}
if(!xmlhttp) {
    alert('Giving up :( Cannot create an XMLHTTP instance');
    return false;
}
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState==4) {
    document.getElementById("chatwindow").innerHTML = xmlhttp.responseText;
    setTimeout("ajax_read()", waittime);
    }
}
xmlhttp.open('GET','methods.php?method=r&room=' + room +'',true);
xmlhttp.send(null);
}
function user_read() {
if(window.XMLHttpRequest){
    xmlhttp3=new XMLHttpRequest();
    if(xmlhttp3.overrideMimeType){
        xmlhttp3.overrideMimeType('text/xml');
    }
} else if(window.ActiveXObject){
    try{
        xmlhttp3=new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
        try{
            xmlhttp3=new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e){
        }
    }
}
if(!xmlhttp3) {
    alert('Giving up :( Cannot create an XMLHTTP instance');
    return false;
}
xmlhttp3.onreadystatechange = function() {
if (xmlhttp3.readyState==4) {
    document.getElementById("userwindow").innerHTML = xmlhttp3.responseText;
    setTimeout("user_read()", 10000);
    }
}
xmlhttp3.open('GET','methods.php?method=u&room=' + room +'',true);
xmlhttp3.send(null);
}
function ajax_write(url){
if(window.XMLHttpRequest){
    xmlhttp2=new XMLHttpRequest();
    if(xmlhttp2.overrideMimeType){
        xmlhttp2.overrideMimeType('text/xml');
    }
} else if(window.ActiveXObject){
    try{
        xmlhttp2=new ActiveXObject("Msxml2.XMLHTTP");
    } catch(e) {
        try{
            xmlhttp2=new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e){
        }
    }
}
if(!xmlhttp2) {
    alert('Giving up :( Cannot create an XMLHTTP instance');
    return false;
}
xmlhttp2.open('GET',url,true);
xmlhttp2.send(null);
}
function submit_msg(){
nick = document.getElementById("chatnick").value;
msg = document.getElementById("chatmsg").value;
document.getElementById("chatmsg").value = "";
ajax_write("methods.php?method=w&m=" + msg + "&n=" + nick + "&room=" + room +    "&sessid=" + sessid + "");
}
function keyup(arg1) { 
if (arg1 == 13) submit_msg(); 
}
var intUpdate = setTimeout("ajax_read()", waittime);
var intUpdate = setTimeout("user_read()", 0);

Answer 1

I’m going to avoid the question slightly and suggest you use jQuery =P. 90% of your code would evaporate. For example, your user_read function would become:

function user_read() {
  $.ajax({
     type: "GET",
     url: "methods.php",
     data: {method: "u", room: room}
     dataType: "html"
     success: function (data, status, xhr) {
         $("#userwindow").html(data);
         setTimeout(user_read, 10000);
     }
   });
}

Furthermore, jQuery is also designed to work on all browsers, so you shouldn’t have IE problems any more.