Q:

Why characters are 'undefined' in internet explorer but not in other browsers

Please take a look at the site tdsoft.se
The script on that page works in opera, firefox chrome etc and prints out "random_1" as it is suposed to do, but in internet explorer it just prints out ("undefinedundefinedundefinedundefinedundefinedundefinedundefinedundefined"), that is 'undefined' for each letter. My question is if some of you bright fellows out there might know the answer to this problem?
EDIT____________________________________________________________
Here's the code
<html>
<head>
<script language="javascript" type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
var txt;
var buildName = "";
var xmlhttp;
/**
 * Find a longest common subsenquence.
 *
 * Note: this is not necessarily the only possible longest common subsequence though!
 */
function lcs(listX, listY) {
        return lcsBackTrack(
                lcsLengths(listX, listY),
                listX, listY, 
                listX.length, listY.length);
}

/**
 * Iteratively memoize a matrix of longest common subsequence lengths.
 */
function lcsLengths(listX, listY) {
        var lenX = listX.length;
        var lenY = listY.length;

        // Initialize a lenX+1 x lenY+1 matrix
        var memo = [lenX+1];
        for (var i = 0; i < lenX+1; i++) {
                memo[i] = [lenY+1];
                for (var j = 0; j < lenY+1; j++) {
                        memo[i][j] = 0;
                }
        }

        // Memoize the lcs length at each position in the matrix
        for (var i = 1; i < lenX+1; i++) {
                for (var j = 1; j < lenY+1; j++) {
                        if (listX[i-1] == listY[j-1]) {
                                memo[i][j] = memo[i-1][j-1] + 1;
                        }
                        else {
                                memo[i][j] = Math.max(
                                        memo[i][j-1],
                                        memo[i-1][j]);
                        }
                }
        }

        return memo;
}

/**
 * Recursively read back a memoized matrix of longest common subsequence lengths
 * to find a longest common subsequence.
 */
function lcsBackTrack(memo, listX, listY, posX, posY) {

        // base case
        if (posX == 0 || posY == 0) {
                return "";
        }

        // matcth => go up and left
        else if (listX [posX-1] == listY[posY-1]) {
                return lcsBackTrack(memo, listX, listY, posX-1, posY-1) + listX[posX-1];
        }

        else {
                // go up
                if (memo[posX][posY-1] > memo[posX-1][posY]) { 
                        return lcsBackTrack(memo, listX, listY, posX, posY-1);
                }

                // go left
                else {
                        return lcsBackTrack(memo, listX, listY, posX-1, posY);
                }
        }
}

function loadXMLDoc(url,cfunc)
{
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=cfunc;
xmlhttp.open("GET",url,true);
xmlhttp.send();
}

function myFunction()
{

    loadXMLDoc("http://tdsoft.se/testni.html",handleXML);

}
var checkState = function(xmlhttp, callback) {

try{
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        callback();
        } 
        else {
            // Check back again 1 sec later
            setTimeout(checkState, 1000);
        }
    }
    catch(err){
        setTimeout(checkState, 1000);
    }
};

function handleXML()
  {
checkState(xmlhttp, function() {

   txt=xmlhttp.responseText;
buildName = "random_1";
var myvar = "";
txt = "" + txt;
var lcsString = lcs(txt, buildName);
document.write(lcsString);
});
  }
</script>
</head>
<body onLoad="myFunction()">
</body>
</html>

A:

This is not working in IE, listX [posX-1]. The result of this is "undefined" so you sould use another way to get the char like chatAt() method

