Ajax timeout issue

prime · November 26, 2008

I have the following code for a chat display app I made and well it works perfectly on some browser but not others, can someone tell me where I went wrong with it please...

I think it's something to do with the recursion, but I'm not 100% sure

<html><head>



<script src="../ajaxrequest.js"></script>
<script langauge="JavaScript">function updatePage()
{ if(request.readyState == 4) {



var xmlobj = request.responseXML
var id = xmlobj.getElementsByTagName("postid")[0].childNodes[0].nodeValue
var user = xmlobj.getElementsByTagName("user")[0].childNodes[0].nodeValue
var message = xmlobj.getElementsByTagName("message")[0].childNodes[0].nodeValue

usermessage = user + ": " + message;

if(previd == undefined)
{
Display = "<p>Welcome to Primefalcon's AJAX chat have a seat and enjoy your stay</p><br /><br />";
}
else if(previd == id)
{
Display = prevdata;
}
else
{
Display = prevdata + "<br />" + usermessage;
}
document.getElementById("pagedisplay").innerHTML = Display;



previd = id;
prevdata = Display;
}}</script>
<style type="text/css">
body
{
background-color: #000066;
}
#pagedisplay
{
color: #000000;
}
</style>
</head><body bgcolor="white"><font color="black">
<script langauge="JavaScript">
var previd;
var prevdata;
function main()
{
	createRequest();
	var serverurl = "server_display.php";
	request.open("GET", serverurl, true);
	request.onreadystatechange = updatePage;
	request.send(null); //just add + for extra info
	setTimeout('main()', '300');
}

main();
</script>

<div id="pagedisplay"></div>

</body></html>

corbin · November 26, 2008

What browser does it not work in?

prime · November 26, 2008

it works in my firefox but not in firefox on a different computer, it also has a problem with opera

corbin · November 26, 2008

My guess would be that the main function is getting executed more than once at a time.

Couple of ways to fix this problem:

-Make the setTimeout('main()', '300'); call in the callback function (updatePage). That way, it will be set to run again right after it finishes.

-Don't rely on global variables. For example, instead of using request in updatePage (since request is a global variable), use this. this can be used since the method is called form inside of the function. Then, it doesn't matter what the outside variable is. Also, make the createRequest() function return a value, not set a global var.

prime · November 26, 2008

1 question, the request as in request is my Ajax object which is...

var request = null;


function createRequest()
{
try
{ request = new XMLHttpRequest(); }

catch(trymicrosoft)
{ try { request = new ActiveXObject("Msxml2.XMLHTTP"); }

catch(othermicrosoft)
{ try { request = new ActiveXObject("Microsoft.XMLHTTP"); }

catch(failed)
{ request = null; } } }  }

corbin · November 27, 2008

I would be more likely to do it like this:

function createRequest() {
var request;
try {
	request = new XMLHttpRequest();
}
catch(trymicrosoft) {
	try {
		request = new ActiveXObject("Msxml2.XMLHTTP");
	}
	catch(othermicrosoft){
		try {
			request = new ActiveXObject("Microsoft.XMLHTTP");
		}
		catch(failed) {
			request = false;
		}
	}
}
}

var request = createRequest();
if(request === false) {
alert("Please get a browser with AJAX support.");
}

If it returns a new instance of an AJAX object, it can be used more easily, and it doesn't rely on a global variable (global variables are evil ;p).

If you want, I can tell you the changes I would make to all of your code.

prime · November 27, 2008

Sure :-) I'm only starting Ajax so I definitely would like to see how someone more experienced would do it better

corbin · November 28, 2008

<html>
<head>
<script src="../ajaxrequest.js"></script>
<script language="JavaScript">
function createRequest() {
var request;
try {
	request = new XMLHttpRequest();
}
catch(trymicrosoft) {
	try {
		request = new ActiveXObject("Msxml2.XMLHTTP");
	}
	catch(othermicrosoft){
		try {
			request = new ActiveXObject("Microsoft.XMLHTTP");
		}
		catch(failed) {
			request = false;
		}
	}
}
return request;
}

function updatePage() {
if(this.readyState == 4) {
	var xmlobj = this.responseXML;
	var id = xmlobj.getElementsByTagName("postid")[0].childNodes[0].nodeValue;
	var user = xmlobj.getElementsByTagName("user")[0].childNodes[0].nodeValue;
	var message = xmlobj.getElementsByTagName("message")[0].childNodes[0].nodeValue;

	usermessage = user + ": " + message;

	if(previd == undefined {
		Display = "<p>Welcome to Primefalcon's AJAX chat have a seat and enjoy your stay</p><br /><br />";
	}
	else if(previd == id) {
		Display = prevdata;
	}
	else
	{
		Display = prevdata + "<br />" + usermessage;
	}
	document.getElementById("pagedisplay").innerHTML = Display;	
	previd = id;
	prevdata = Display;
	setTimeout('main()', '300');
}
}

var previd;
var prevdata;
function main() {
var request = createRequest();
var serverurl = "server_display.php";
request.open("GET", serverurl, true);
request.onreadystatechange = updatePage;
request.send(null); //just add + for extra info
}

</script>
<style type="text/css">
body {
background-color: #000066;
color: black;
}
#pagedisplay {
color: #000000;
}
</style>
</head>
<body bgcolor="white">
<script language="JavaScript">
	main();
</script>

<div id="pagedisplay"></div>

</body>
</html>

Oh, you misspelled language every time it was in there by the way x.x.

Anyway that's more-ish how I would do it.

prime · December 2, 2008

Thx :-) and dang it your right about the language, thx for pointing that outm that'll help a lot

corbin · December 2, 2008

Eh, I wouldn't have caught it if not for syntax highlighting ;p.

No problem.

prime · December 2, 2008

eh I use VI or gedit mostly since I'm using a Linux os, and both of those have syntax highlighting so unfortunately for me, I can't use that :-[

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