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10.4 AJAX 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

Select a CD:  
CD info will be listed here...

 Select a CD: Bob Dylan 
TITLE: Empire Burlesque
ARTIST: Bob Dylan
COUNTRY: USA
COMPANY: Columbia
PRICE: 10.90
YEAR: 1985

 Select a CD: Bee Gees 
TITLE: One night only
ARTIST: Bee Gees
COUNTRY: UK
COMPANY: Polydor
PRICE: 10.90
YEAR: 1998

 Select a CD: Cat Stevens 
TITLE: The very best of
ARTIST: Cat Stevens
COUNTRY: UK
COMPANY: Island
PRICE: 8.90
YEAR: 1990

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">CD info will be listed here...</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)

PHP Fundamentals Course Menu
Module 10. PHP - AJAX

Navigate this module

Eventually the navigation links, above, will be replaced by these << (previous) and >> (next) buttons below.

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Example files created in this module:
AJAX PHP Example AJAX Database - Example Explained links.xml