PHP Example - AJAX and XML

AJAX can be used for interactive communication with an XML file.

AJAX XML Example

The following example will demonstrate how a web page can fetch information from an XML file with AJAX:

Example Explained - The HTML Page

When a user selects a CD in the dropdown list above, a function called "showCD()" is executed. The function is triggered by the "onchange" event:

< html>
< head>
< script>
function showCD(str) {
  if (str=="") {
    document.getElementById("txtHint").innerHTML="";
    return;
  }
  var xmlhttp=new XMLHttpRequest();
  xmlhttp.onreadystatechange=function() {
    if (this.readyState==4 && this.status==200) {
      document.getElementById("txtHint").innerHTML=this.responseText;
    }
  }
  xmlhttp.open("GET","getcd.php?q="+str,true);
  xmlhttp.send();
}
< /script>
< /head>
< body>

< form>
Select a CD:
< select name="cds" onchange="showCD(this.value)">
  < option value="">Select a CD:< /option>
  < option value="Bob Dylan">Bob Dylan< /option>
  < option value="Bee Gees">Bee Gees< /option>
  < option value="Cat Stevens">Cat Stevens< /option>
< /select>
< /form>
< div id="txtHint">< b>CD info will be listed here...< /b>< /div>

< /body>
< /html>

The showCD() function does the following:

• Check if a CD is selected
• Create an XMLHttpRequest object
• Create the function to be executed when the server response is ready
• Send the request off to a file on the server
• Notice that a parameter (q) is added to the URL (with the content of the dropdown list)

The PHP File

The page on the server called by the JavaScript above is a PHP file called "getcd.php".
The PHP script loads an XML document, "cd_catalog.xml", runs a query against the XML file, and returns the result as HTML:

< ?php
$q=$_GET["q"];

$xmlDoc = new DOMDocument();
$xmlDoc->load("cd_catalog.xml");

$x=$xmlDoc->getElementsByTagName('ARTIST');

for ($i=0; $i<=$x->length-1; $i++) {
  //Process only element nodes
  if ($x->item($i)->nodeType==1) {
    if ($x->item($i)->childNodes->item(0)->nodeValue == $q) {
      $y=($x->item($i)->parentNode);
    }
  }
}

$cd=($y->childNodes);

for ($i=0;$i< $cd->length;$i++) {
  //Process only element nodes
  if ($cd->item($i)->nodeType==1) {
    echo("< b>" . $cd->item($i)->nodeName . ":< /b> ");
    echo($cd->item($i)->childNodes->item(0)->nodeValue);
    echo("< br>");
  }
}
?>

When the CD query is sent from the JavaScript to the PHP page, the following happens:

1. PHP creates an XML DOM object
2. Find all < artist> elements that matches the name sent from the JavaScript
3. Output the album information (send to the "txtHint" placeholder)