Question

I am trying to use AJAX for the first time, and I am having a difficult time getting the hang of it. Here is the request code:

function requestData(j) {
    var xmlhttp;
        if (window.XMLHttpRequest) {
            xmlhttp=new XMLHttpRequest();
        }
        xmlhttp.onreadystatechange = function() {
                if (xmlhttp.readyState==4 && xmlhttp.status==200) {
                    xml = xmlhttp.responseXML;
                    post = "";
                    title = "";
                    postdata = xml.getElementsByTagName("post");
                    titledata = xml.getElementsByTagName("title");
                    datedata = xml.getElementsByTagName("date");
                    timedata = xml.getElementsByTagName("time");
                    document.getElementById("post").value = postdata[0].childNodes[0].nodeValue;
                    document.getElementById("heading").value = titledata[0].childNodes[0].nodeValue;
                    document.getElementById("date").value = datedata[0].childNodes[0].nodeValue;
                    document.getElementById("time").value = timedata[0].childNodes[0].nodeValue;
                    document.getElementById("id").value = j;
                    document.getElementById("update").value = "true";
                }
            };
        xmlhttp.open("POST","../script/getnewsdata.php",true);
        xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
        xmlhttp.send("ID=" + j);
        return false;
    }

Firebug is telling me that “xml is null” on the line postdata = xml.getElementsByTagName(“post”); Which means that xmlhttp.responseXML is null.

This is the server side script:

<?php
$db = mysql_connect("wadafw","awfawf","awfsgv");
if(!$db)
{
  die("Could not connect: " . mysql_error());
}
mysql_select_db("afggbare", $db);
$updata = mysql_query('SELECT * FROM News WHERE NewsID='.$_POST['ID']);
$blog = mysql_fetch_array($updata);
$post = $blog['Content'];
$regex = Array('/<br />/', '/<(\/?)(b|i|u)>/', '/<a href="(http://[www.]?\w+)">(\w+)<\/a>/', '/<div class="media"><iframe title="YouTube video player" width="425" height="265" src="http://www.youtube.com/embed/(\w+)hd=1" frameborder="0" allowfullscreen></iframe></div>/', '/<div class="media"><img width="425" src="(http://[www.]?[\w+])" /></div>/');
$regReplace = Array('\r\n', '[$1$2]', '[link=$1]$2[/link]', '[youtube]http://www.youtube.com/watch?v=$1[/youtube]',
                '[img]$1[/img]');
$post = preg_replace($regex, $regReplace, $post);

echo    '<newsItem>
        <title>'.$blog['Heading'].'</title>
        <post>'.$post.'</post>
        <date>'.$blog['time'].'</date>
        <time>'.$blog['time'].'</time>
    </newsItem>';
?>

The regex is probably bad… but that’s not important right now.

Changed to this… and now getting “function not defined” errors:

function requestData(j) {
        $.ajax("../script/getnewsdata.php", {
            data: {ID: j},
            type: "POST",
            dataType: "xml",
            success: function(data, status, jqXHR){
                var xml = jqXHR.responseXML;
                postdata = xml.getElementsByTagName("post");
                titledata = xml.getElementsByTagName("title");
                datedata = xml.getElementsByTagName("date");
                timedata = xml.getElementsByTagName("time");
                document.getElementById("post").value = postdata[0].childNodes[0].nodeValue;
                document.getElementById("heading").value = titledata[0].childNodes[0].nodeValue;
                document.getElementById("date").value = datedata[0].childNodes[0].nodeValue;
                document.getElementById("time").value = timedata[0].childNodes[0].nodeValue;
                document.getElementById("id").value = j;
                document.getElementById("update").value = "true";
            }


        }
    }

Okay, found that problem. It was just a typo… hadn’t closed the $.ajax() parameter brackets. Now I am not getting errors. But it just doesn’t do anything…

Answer 1

Instead of trying to get AJAX running from scratch, I’d recommend using an existing library. jQuery makes this task extremely easy.

http://api.jquery.com/jQuery.ajax/

function requestData(j) {
    $.ajax('../script/getnewsdata.php', {
        data: {ID: j},
        type: 'POST',
        dataType: 'xml',
        success: function(data, status, jqXHR){
            // consume data here
        }
    });
}