AJAX = Asynchronous JavaScript and XML.
AJAX is not a new programming language, but a new way to use existing standards.
AJAX is the art of exchanging data with a server, and update parts of a web page without reloading the whole page.
AJAX Introduction
AJAX is about updating parts of a web page, without reloading the whole page.
Before you continue you should have a basic understanding of the following:
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HTML / XHTML
CSS
JavaScript / DOM
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.
AJAX is Based on Internet Standards
AJAX is based on internet standards, and uses a combination of:
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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 - Create an XMLHttpRequest Object
The keystone of AJAX is the XMLHttpRequest object.
The XMLHttpRequest Object
All modern browsers support the XMLHttpRequest object (IE5 and IE6 uses an ActiveXObject).
The XMLHttpRequest object is used to exchange data with a server behind the scenes. This means that it is
possible to update parts of a web page, without reloading the whole page.
Create an XMLHttpRequest Object
All modern browsers (IE7+, Firefox, Chrome, Safari, and Opera) have a built-in XMLHttpRequest object.
Syntax for creating an XMLHttpRequest object:
xmlhttp=new XMLHttpRequest();
Old versions of Internet Explorer (IE5 and IE6) uses an ActiveX Object:
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
AJAX - Send a Request To a Server
The XMLHttpRequest object is used to exchange data with a server
Send a Request To a Server
To send a request to a server, we use the open() and send() methods of the XMLHttpRequest object:
xmlhttp.open("GET","ajax_info.txt",true);
xmlhttp.send();
GET or POST?
GET is simpler and faster than POST, and can be used in most cases.
However, always use POST requests when:
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A cached file is not an option (update a file or database on the server)
Sending a large amount of data to the server (POST has no size limitations)
Sending user input (which can contain unknown characters), POST is more robust and secure than
GET
GET Requests
A simple GET request:
xmlhttp.open("GET","ajax_test.asp",true);
Example
xmlhttp.open("GET","demo_get.asp",true);
xmlhttp.send();
POST Requests
xmlhttp.open("POST","demo_post.asp",true);
xmlhttp.send();
The url - A File On a Server
Asynchronous - True or False?
AJAX stands for Asynchronous JavaScript and XML, and for the XMLHttpRequest object to behave as AJAX,
the async parameter of the open() method has to be set to true Sending asynchronously requests is a huge
improvement for web developers. Many of the tasks performed on the server are very time consuming.
Before AJAX, this operation could cause the application to hang or stop.
With AJAX, the JavaScript does not have to wait for the server response, but can instead:
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execute other scripts while waiting for server response
deal with the response when the response ready
Async=true
When using async=true, specify a function to execute when the response is ready in the
onreadystatechange event:
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","ajax_info.txt",true);
xmlhttp.send();
You will learn more about onreadystatechange in a later chapter.
Async=false
To use async=false, change the third parameter in the open() method to false:
xmlhttp.open("GET","ajax_info.txt",false);
Using async=false is not recommended, but for a few small requests this can be ok.
Remember that the JavaScript will NOT continue to execute, until the server response is ready. If the server
is busy or slow, the application will hang or stop.
Note: When you use async=false, do NOT write an onreadystatechange function - just put the code after
the send() statement:
xmlhttp.open("GET","ajax_info.txt",false);
xmlhttp.send();
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
AJAX - Server Response
Server Response
To get the response from a server, use the responseText or responseXML property of the XMLHttpRequest
object.
Property
Description
responseText
get the response data as a string
responseXML
get the response data as XML data
The responseText Property
If the response from the server is not XML, use the responseText property.
The responseText property returns the response as a string, and you can use it accordingly:
Example
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
The responseXML Property
If the response from the server is XML, and you want to parse it as an XML object, use the responseXML
property:
Example
Request the file cd_catalog.xml and parse the response:
xmlDoc=xmlhttp.responseXML;
var txt="";
x=xmlDoc.getElementsByTagName("ARTIST");
for (i=0;i<x.length;i++)
{
txt=txt + x[i].childNodes[0].nodeValue + "<br />";
}
document.getElementById("myDiv").innerHTML=txt;
AJAX - The onreadystatechange Event
The onreadystatechange event
When a request to a server is sent, we want to perform some actions based on the response.
The onreadystatechange event is triggered every time the readyState changes.
The readyState property holds the status of the XMLHttpRequest.
Three important properties of the XMLHttpRequest object:
Property
Description
onreadystatechange Stores a function (or the name of a function) to be called automatically each time the
readyState property changes
readyState
Holds the status of the XMLHttpRequest. Changes from 0 to 4:
0: request not initialized
1: server connection established
2: request received
3: processing request
4: request finished and response is ready
status
200: "OK"
404: Page not found
In the onreadystatechange event, we specify what will happen when the server response is ready to be
processed.
When readyState is 4 and status is 200, the response is ready:
Example
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
Note: The onreadystatechange event is triggered four times, one time for each change in readyState.
AJAX ASP/PHP Example
AJAX is used to create more interactive applications.
AJAX PHP Example
The following example will demonstrate how a web page can communicate with a web server while a user
type characters in an input field:
Example Explained - The showHint() Function
When a user types a character in the input field above, the function "showHint()" is executed. The function
is triggered by the "onkeyup" event:
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();
}
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:
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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 AJAX Server Page - PHP
The page on the server called by the JavaScript above is an PHP file called "gethint.php".
Below we have created two versions of the server file, one written in ASP and one in PHP.
The PHP File
Below is the code above rewritten in PHP.
Note: To run the example in PHP, change the value of the url variable (in the HTML file) from "gethint.asp"
to "gethint.php".
<?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;
?>
AJAX Database Example
AJAX can be used for interactive communication with a database.
how a web page can fetch information from a database with AJAX
Example Explained - The showCustomer() Function
When a user selects a customer in the dropdown list above, a function called "showCustomer()" is
executed. The function is triggered by the "onchange" event:
Example:- Ajax
function showCustomer(str)
{
if (str=="")
{
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","getcustomer.php?q="+str,true);
xmlhttp.send();
}
The showCustomer() function does the following:
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Check if a customer 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)
It has three point to explain ajax with php.
1.
2.
3.
4.
First to create form for search.
Second to create ajax for server side file access.
Third to create database in localhost and insert data.
create php file for database handling and display data.
Example:-form.html
<html>
<head>
<script src=”ajax.aj”></script>
<title>
</title>
</head>
<body>
<form>
<select name="users" onChange="showUser(this.value)">
<option value="">Select a person:</option>
<option value="1">sumit</option>
<option value="2">anil</option>
<option value="3">ramesh</option>
<option value="4">karan</option>
</select>
</form>
<br />
<div id="txtHint"><b>Person info will be listed here.</b></div>
</body>
</html>
Ajax file
function showUser(str)
{
if (str=="")
{
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","record.php?q="+str,true);
xmlhttp.send();
}
Php file=record.php
<?php
$q=$_GET["q"];
$con = mysql_connect("localhost", "root","vertrigo");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
mysql_select_db("record", $con);
$sql="select * from employee where id= '".$q."'";
$result = mysql_query($sql);
echo "<table border='1'>
<tr>
<th>Firstname</th>
<th>Lastname</th>
<th>Age</th>
<th>Address</th>
<th>Email</th>
</tr>";
while($row = mysql_fetch_array($result))
{
echo "<tr>";
echo "<td>" . $row['first_name'] . "</td>";
echo "<td>" . $row['last_name'] . "</td>";
echo "<td>" . $row['age'] . "</td>";
echo "<td>" . $row['address'] . "</td>";
echo "<td>" . $row['email'] . "</td>";
echo "</tr>";
}
echo "</table>";
mysql_close($con);
?>
Database:Database name=record
Table name=employee
Fields=id,first_name,last_name,age,address,email.