What is AJAX?
AJAX = Asynchronous JavaScript and XML.
AJAX is a technique for creating fast and dynamic web pages.
AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.
Classic web pages, (which do not use AJAX) must reload the entire page if the content should change.
Examples of applications using AJAX: Google Maps, Gmail, Youtube, and Facebook tabs.
AJAX is Based on Internet Standards
AJAX is based on internet standards, and uses a combination of:
XMLHttpRequest object (to exchange data asynchronously with a server)
JavaScript/DOM (to display/interact with the information)
CSS (to style the data)
XML (often used as the format for transferring data)
AJAX applications are browser- and platform-independent!
Google Suggest
AJAX was made popular in 2005 by Google, with Google Suggest.
Google Suggest is using AJAX to create a very dynamic web interface: When you start typing in Google's search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions.
Start Using AJAX Today
In our PHP tutorial, we will demonstrate how AJAX can update parts of a web page, without reloading the whole page. The server script will be written in PHP.
If you want to learn more about AJAX, visit our AJAX tutorial.
Example Explained - The HTML Page
When a user types a character in the input field above, the function "showHint()" is executed. The function is triggered by the "onkeyup" event:
<html>
<head>
<script>
function showHint(str)
{
if (str.length==0)
{
document.getElementById("txtHint").innerHTML="";
return;
}
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 && xmlhttp.status==200)
{
document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","gethint.php?q="+str,true);
xmlhttp.send();
}
</script>
</head>
<body>
<p><b>Start typing a name in the input field below:</b></p>
<form>
First name: <input type="text" > </form>
<p>Suggestions: <span id="txtHint"></span></p>
</body>
</html>
Source code explanation:
If the input field is empty (str.length==0), the function clears the content of the txtHint placeholder and exits the function.
If the input field is not empty, the showHint() function executes the following:
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 input field)
The PHP File
The page on the server called by the JavaScript above is a PHP file called "gethint.php".
The source code in "gethint.php" checks an array of names, and returns the corresponding name(s) to the browser:
<?php
// Fill up array with names
$a[]="Anna";
$a[]="Brittany";
$a[]="Cinderella";
$a[]="Diana";
$a[]="Eva";
$a[]="Fiona";
$a[]="Gunda";
$a[]="Hege";
$a[]="Inga";
$a[]="Johanna";
$a[]="Kitty";
$a[]="Linda";
$a[]="Nina";
$a[]="Ophelia";
$a[]="Petunia";
$a[]="Amanda";
$a[]="Raquel";
$a[]="Cindy";
$a[]="Doris";
$a[]="Eve";
$a[]="Evita";
$a[]="Sunniva";
$a[]="Tove";
$a[]="Unni";
$a[]="Violet";
$a[]="Liza";
$a[]="Elizabeth";
$a[]="Ellen";
$a[]="Wenche";
$a[]="Vicky";
//get the q parameter from URL
$q=$_GET["q"];
//lookup all hints from array if length of q>0
if (strlen($q) > 0)
{
$hint="";
for($i=0; $i<count($a); $i++)
{
if (strtolower($q)==strtolower(substr($a[$i],0,strlen($q))))
{
if ($hint=="")
{
$hint=$a[$i];
}
else
{
$hint=$hint." , ".$a[$i];
}
}
}
}
// Set output to "no suggestion" if no hint were found
// or to the correct values
if ($hint == "")
{
$response="no suggestion";
}
else
{
$response=$hint;
}
//output the response
echo $response;
?>
Explanation: If there is any text sent from the JavaScript (strlen($q) > 0), the following happens:
Find a name matching the characters sent from the JavaScript
If no match were found, set the response string to "no suggestion"
If one or more matching names were found, set the response string to all these names
The response is sent to the "txtHint" placeholder
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