How do I get the XMLhttp responseText?
<p>I am not too familiar with the xmlhttp object, and despite the available documentation, am having trouble getting the <code>responseText</code>. Am so close, but would appreciate anyone who could point out why the following does not work; after the <code>send()</code> it just dies...: </p>

<pre><code>function fetchgenotype() {
    // here's where we use an Ajax function to fetch the allele values without reloading the page.
    // Get the index number of the genotype record to retrieve; retrieve it; populate the alleles.
    var mndx, sndx = 0;
    mndx = $('#marker').val();
    if (Study_selected) {
        sndx = $('#stylabid').val();
    } else {
        sndx = $('#pjtlabid').val();
    }
    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 = function () {
        if (xmlhttp.readyState == 4 &amp;&amp; xmlhttp.status == 200) {
            // Recieve the return value, parse and assign to screen form. 
            var allele_stg = "";
            allele_stg = document.getElementById("allele_ary").innerHTML = xmlhttp.responseText;
            ary = new Array();
            ary = str_getcsv(allele_ary, ',');
            $('#allele_1_1').val() = ary[0];
            $('#allele_1_2').val() = ary[1];
        }
    }
    xmlhttp.open("GET", "fetchAlleles.php?mndx=" + mndx + "&amp;sndx=" + sndx, true);
    xmlhttp.send();
} // end of fetchgenotype
</code></pre>
