Ajax tutorial

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AbouttheTutorial
AJAX is a web development technique for creating interactive web applications.
If you know JavaScript, HTML, CSS, and XML, then you need to spend just one
hour to start with AJAX.
Audience
This tutorial will be useful for web developers who want to learn how to create
interactive webpages as well as improve their speed and usability using AJAX.
Prerequisites
It is highly recommended that you are familiar with HTML and JavaScript before
attempting this tutorial.
Copyright&Disclaimer
 Copyright 2015 by Tutorials Point (I) Pvt. Ltd.
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Tutorials Point (I) Pvt. Ltd. The user of this e-book is prohibited to reuse, retain,
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any manner without written consent of the publisher.
We strive to update the contents of our website and tutorials as timely and as
precisely as possible, however, the contents may contain inaccuracies or errors.
Tutorials Point (I) Pvt. Ltd. provides no guarantee regarding the accuracy,
timeliness or completeness of our website or its contents including this tutorial.
If you discover any errors on our website or in this tutorial, please notify us at
contact@tutorialspoint.com

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TableofContents
About the Tutorial .....................................................................................................................................i
Audience....................................................................................................................................................i
Prerequisites..............................................................................................................................................i
Copyright & Disclaimer ..............................................................................................................................i
Table of Contents......................................................................................................................................ii
1. OVERVIEW ............................................................................................................................1
Rich Internet Application Technology .......................................................................................................1
AJAX is Based on Open Standards.............................................................................................................1
2. TECHNOLOGIES USED IN AJAX ..............................................................................................3
JavaScript..................................................................................................................................................3
DOM .........................................................................................................................................................3
CSS............................................................................................................................................................3
XMLHttpRequest.......................................................................................................................................3
3. EXAMPLES.............................................................................................................................4
Google Maps.............................................................................................................................................4
Google Suggest .........................................................................................................................................4
Gmail ........................................................................................................................................................4
Yahoo Maps (new)....................................................................................................................................4
Difference between AJAX and Conventional CGI Program ........................................................................4
4. BROWSER SUPPORT..............................................................................................................6
Writing Browser Specific Code ..................................................................................................................6
5. AJAX IN ACTION ....................................................................................................................8
Steps of AJAX Operation ...........................................................................................................................8
A Client Event Occurs................................................................................................................................8

iii
The XMLHttpRequest Object is Created ....................................................................................................8
The XMLHttpRequest Object is Configured ...............................................................................................9
Making Asynchronous Request to the Webserver.....................................................................................9
Webserver Returns the Result Containing XML Document .....................................................................10
Callback Function processRequest() is Called ..........................................................................................11
The HTML DOM is Updated.....................................................................................................................11
6. XMLHTTPREQUEST..............................................................................................................13
XMLHttpRequest Methods......................................................................................................................13
XMLHttpRequest Properties ...................................................................................................................14
7. DATABASE OPERATIONS .....................................................................................................16
Client Side HTML File ..............................................................................................................................16
Server Side PHP File ................................................................................................................................19
8. SECURITY ............................................................................................................................22
AJAX Security: Server Side ......................................................................................................................22
AJAX Security: Client Side .......................................................................................................................22
9. CURRENT ISSUES.................................................................................................................23

Ajax
1
AJAX stands for Asynchronous JavaScript and XML. AJAX is a new technique for
creating better, faster, and more interactive web applications with the help of
XML, HTML, CSS, and Java Script.
 Ajax uses XHTML for content, CSS for presentation, along with Document
Object Model and JavaScript for dynamic content display.
 Conventional web applications transmit information to and from the sever
using synchronous requests. It means you fill out a form, hit submit, and
get directed to a new page with new information from the server.
 With AJAX, when you hit submit, JavaScript will make a request to the
server, interpret the results, and update the current screen. In the purest
sense, the user would never know that anything was even transmitted to
the server.
 XML is commonly used as the format for receiving server data, although
any format, including plain text, can be used.
 AJAX is a web browser technology independent of web server software.
 A user can continue to use the application while the client program
requests information from the server in the background.
 Intuitive and natural user interaction. Clicking is not required, mouse
movement is a sufficient event trigger.
 Data-driven as opposed to page-driven.
RichInternetApplicationTechnology
AJAX is the most viable Rich Internet Application (RIA) technology so far. It is
getting tremendous industry momentum and several tool kit and frameworks are
emerging. But at the same time, AJAX has browser incompatibility and it is
supported by JavaScript, which is hard to maintain and debug.
AJAXisBasedonOpenStandards
AJAX is based on the following open standards:
 Browser-based presentation using HTML and Cascading Style Sheets
(CSS).
 Data is stored in XML format and fetched from the server.
1. OVERVIEW

Ajax
2
 Behind-the-scenes data fetches using XMLHttpRequest objects in the
browser.
 JavaScript to make everything happen.

Ajax
3
AJAX cannot work independently. It is used in combination with other
technologies to create interactive webpages.
JavaScript
 Loosely typed scripting language.
 JavaScript function is called when an event occurs in a page.
 Glue for the whole AJAX operation.
DOM
 API for accessing and manipulating structured documents.
 Represents the structure of XML and HTML documents.
CSS
 Allows for a clear separation of the presentation style from the content
and may be changed programmatically by JavaScript.
XMLHttpRequest
 JavaScript object that performs asynchronous interaction with the server.
2. TECHNOLOGIES USED IN AJAX

Ajax
4
Here is a list of some famous web applications that make use of AJAX.
GoogleMaps
A user can drag an entire map by using the mouse, rather than clicking on a
button.
 http://maps.google.com/
GoogleSuggest
As you type, Google offers suggestions. Use the arrow keys to navigate the
results.
 http://www.google.com/webhp?complete=1&hl=en
Gmail
Gmail is a webmail built on the idea that emails can be more intuitive, efficient,
and useful.
 http://gmail.com/
YahooMaps(new)
Now it's even easier and more fun to get where you're going!
 http://maps.yahoo.com/
DifferencebetweenAJAXandConventionalCGIProgram
Try these two examples one by one and you will feel the difference. While trying
AJAX example, there is no discontinuity and you get the response very quickly,
but when you try the standard GCI example, you would have to wait for the
response and your page also gets refreshed.
AJAX Example:
* =
Submit
3. EXAMPLES

Ajax
5
Standard Example:
* =
Submit
NOTE: We have given a more complex example in AJAX Database.

Ajax
6
All the available browsers cannot support AJAX. Here is a list of major browsers
that support AJAX.
 Mozilla Firefox 1.0 and above.
 Netscape version 7.1 and above.
 Apple Safari 1.2 and above.
 Microsoft Internet Explorer 5 and above.
 Konqueror.
 Opera 7.6 and above.
When you write your next application, do consider the browsers that do not
support AJAX.
NOTE: When we say that a browser does not support AJAX, it simply means
that the browser does not support the creation of Javascript object –
XMLHttpRequest object.
WritingBrowserSpecificCode
The simplest way to make your source code compatible with a browser is to
use try...catch blocks in your JavaScript.
<html>
<body>
<script language="javascript" type="text/javascript">
<!--
//Browser Support Code
function ajaxFunction(){
var ajaxRequest; // The variable that makes Ajax possible!
try{
// Opera 8.0+, Firefox, Safari
ajaxRequest = new XMLHttpRequest();
}catch (e){
// Internet Explorer Browsers
4. BROWSER SUPPORT

Ajax
7
try{
ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
}catch (e) {
try{
ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
}catch (e){
// Something went wrong
alert("Your browser broke!");
return false;
}
}
}
}
//-->
</script>
<form name='myForm'>
Name: <input type='text' name='username' /> <br />
Time: <input type='text' name='time' />
</form>
</body>
</html>
In the above JavaScript code, we try three times to make our XMLHttpRequest
object. Our first attempt:
 ajaxRequest = new XMLHttpRequest();
It is for Opera 8.0+, Firefox, and Safari browsers. If it fails, we try two more
times to make the correct object for an Internet Explorer browser with:
 ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
 ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
If it doesn't work, then we can use a very outdated browser that doesn't support
XMLHttpRequest, which also means it doesn't support AJAX.
Most likely though, our variable ajaxRequest will now be set to whatever
XMLHttpRequest standard the browser uses and we can start sending data to the
server. The step-wise AJAX workflow is explained in the next chapter.

Ajax
8
This chapter gives you a clear picture of the exact steps of AJAX operation.
StepsofAJAXOperation
1. A client event occurs.
2. An XMLHttpRequest object is created.
3. The XMLHttpRequest object is configured.
4. The XMLHttpRequest object makes an asynchronous request to the
Webserver.
5. The Webserver returns the result containing XML document.
6. The XMLHttpRequest object calls the callback() function and processes the
result.
7. The HTML DOM is updated.
Let us take these steps one by one.
AClientEventOccurs
 A JavaScript function is called as the result of an event.
 Example: validateUserId() JavaScript function is mapped as an event
handler to an onkeyup event on input form field whose id is set to
"userid".
 <input type="text" size="20" id="userid" name="id"
onkeyup="validateUserId();">.
TheXMLHttpRequestObjectisCreated
try{
}catch (e){
5. AJAX IN ACTION

Ajax
9
try{
}catch (e) {
try{
}catch (e){
return false;
}
}
}
}
TheXMLHttpRequestObjectisConfigured
In this step, we will write a function that will be triggered by the client event and
a callback function processRequest() will be registered.
function validateUserId() {
ajaxFunction();
// Here processRequest() is the callback function.
ajaxRequest.onreadystatechange = processRequest;
if (!target) target = document.getElementById("userid");
var url = "validate?id=" + escape(target.value);
ajaxRequest.open("GET", url, true);
ajaxRequest.send(null);
}
MakingAsynchronousRequesttotheWebserver
Source code is available in the above piece of code. Code written in bold
typeface is responsible to make a request to the webserver. This is all being
done using the XMLHttpRequest object ajaxRequest.

Ajax
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function validateUserId() {
ajaxFunction();
// Here processRequest() is the callback function.
ajaxRequest.onreadystatechange = processRequest;
if (!target) target = document.getElementById("userid");
var url = "validate?id=" + escape(target.value);
ajaxRequest.open("GET", url, true);
}
Assume you enter Zara in the userid box, then in the above request, the URL is
set to "validate?id=Zara".
WebserverReturnstheResultContainingXMLDocument
You can implement your server-side script in any language, however its logic
should be as follows.
 Get a request from the client.
 Parse the input from the client.
 Do required processing.
 Send the output to the client.
If we assume that you are going to write a servlet, then here is the piece of
code.
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
String targetId = request.getParameter("id");
if ((targetId != null) && !accounts.containsKey(targetId.trim()))
{
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
response.getWriter().write("true");
}

Ajax
11
else
{
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
response.getWriter().write("false");
}
}
CallbackFunctionprocessRequest()isCalled
The XMLHttpRequest object was configured to call the processRequest() function
when there is a state change to the readyState of the XMLHttpRequest object.
Now this function will receive the result from the server and will do the required
processing. As in the following example, it sets a variable message on true or
false based on the returned value from the Webserver.
function processRequest() {
if (req.readyState == 4) {
if (req.status == 200) {
var message = ...;
...
}
TheHTMLDOMisUpdated
This is the final step and in this step, your HTML page will be updated. It
happens in the following way:
 JavaScript gets a reference to any element in a page using DOM API.
 The recommended way to gain a reference to an element is to call.
document.getElementById("userIdMessage"),
// where "userIdMessage" is the ID attribute
// of an element appearing in the HTML document
 JavaScript may now be used to modify the element's attributes; modify
the element's style properties; or add, remove, or modify the child
elements. Here is an example:
<script type="text/javascript">

Ajax
12

</script>
<body>
<div id="userIdMessage"><div>
</body>
If you have understood the above-mentioned seven steps, then you are almost
done with AJAX. In the next chapter, we will see XMLHttpRequest object in
detail.

Ajax
13
The XMLHttpRequest object is the key to AJAX. It has been available ever since
Internet Explorer 5.5 was released in July 2000, but was not fully discovered
until AJAX and Web 2.0 in 2005 became popular.
XMLHttpRequest (XHR) is an API that can be used by JavaScript, JScript,
VBScript, and other web browser scripting languages to transfer and manipulate
XML data to and from a webserver using HTTP, establishing an independent
connection channel between a webpage's Client-Side and Server-Side.
The data returned from XMLHttpRequest calls will often be provided by back-end
databases. Besides XML, XMLHttpRequest can be used to fetch data in other
formats, e.g. JSON or even plain text.
You already have seen a couple of examples on how to create an
XMLHttpRequest object.
Listed below are some of the methods and properties that you have to get
familiar with.
XMLHttpRequestMethods
 abort()
Cancels the current request.
 getAllResponseHeaders()
Returns the complete set of HTTP headers as a string.
 getResponseHeader( headerName )
Returns the value of the specified HTTP header.
 open( method, URL )
 open( method, URL, async )
 open( method, URL, async, userName )
 open( method, URL, async, userName, password )
Specifies the method, URL, and other optional attributes of a request.
6. XMLHTTPREQUEST

Ajax
14
The method parameter can have a value of "GET", "POST", or "HEAD".
Other HTTP methods such as "PUT" and "DELETE" (primarily used in REST
applications) may be possible.
The "async" parameter specifies whether the request should be handled
asynchronously or not. "true" means that the script processing carries on
after the send() method without waiting for a response, and "false" means
that the script waits for a response before continuing script processing.
 send( content )
Sends the request.
 setRequestHeader( label, value )
Adds a label/value pair to the HTTP header to be sent.
XMLHttpRequestProperties
 onreadystatechange
An event handler for an event that fires at every state change.
 readyState
The readyState property defines the current state of the XMLHttpRequest
object.
The following table provides a list of the possible values for the readyState
property:
State Description
0 The request is not initialized.
1 The request has been set up.
2 The request has been sent.
3 The request is in process.
4 The request is completed.
readyState = 0 – After you have created the XMLHttpRequest object, but
before you have called the open() method.

Ajax
15
readyState = 1 After you have called the open() method, but before
you have called send().
readyState = 2 After you have called send().
readyState = 3 After the browser has established a communication
with the server, but before the server has completed the response.
readyState = 4 After the request has been completed, and the
response data has been completely received from the server.
 responseText
Returns the response as a string.
 responseXML
Returns the response as XML. This property returns an XML document
object, which can be examined and parsed using the W3C DOM node tree
methods and properties.
 status
Returns the status as a number (e.g., 404 for "Not Found" and 200 for
"OK").
 statusText
Returns the status as a string (e.g., "Not Found" or "OK").

Ajax
16
To clearly illustrate how easy it is to access information from a database using
AJAX, we are going to build MySQL queries on the fly and display the results on
"ajax.html". But before we proceed, let us do the ground work. Create a table
using the following command.
NOTE: We are assuming you have sufficient privilege to perform the following
MySQL operations.
CREATE TABLE 'ajax_example' (
'name' varchar(50) NOT NULL,
'age' int(11) NOT NULL,
'sex' varchar(1) NOT NULL,
'wpm' int(11) NOT NULL,
PRIMARY KEY ('name')
)
Now dump the following data into this table using the following SQL statements:
INSERT INTO 'ajax_example' VALUES ('Jerry', 120, 'm', 20);
INSERT INTO 'ajax_example' VALUES ('Regis', 75, 'm', 44);
INSERT INTO 'ajax_example' VALUES ('Frank', 45, 'm', 87);
INSERT INTO 'ajax_example' VALUES ('Jill', 22, 'f', 72);
INSERT INTO 'ajax_example' VALUES ('Tracy', 27, 'f', 0);
INSERT INTO 'ajax_example' VALUES ('Julie', 35, 'f', 90);
ClientSideHTMLFile
Now let us have our client side HTML file, which is ajax.html, and it will have the
following code:
<html>
<body>
<script language="javascript" type="text/javascript">
<!--
//Browser Support Code
7. DATABASE OPERATIONS

Ajax
17
try{
}catch (e){
try{
}catch (e) {
try{
}catch (e){
return false;
}
}
}
// Create a function that will receive data
// sent from the server and will update
// div section in the same page.
ajaxRequest.onreadystatechange = function(){
if(ajaxRequest.readyState == 4){
var ajaxDisplay = document.getElementById('ajaxDiv');
ajaxDisplay.innerHTML = ajaxRequest.responseText;
}
}
// Now get the value from user and pass it to
// server script.
var age = document.getElementById('age').value;
var wpm = document.getElementById('wpm').value;
var sex = document.getElementById('sex').value;

Ajax
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var queryString = "?age=" + age ;
queryString += "&wpm=" + wpm + "&sex=" + sex;
ajaxRequest.open("GET", "ajax-example.php" + queryString, true);
}
//-->
</script>
<form name='myForm'>
Max Age: <input type='text' id='age' /> <br />
Max WPM: <input type='text' id='wpm' />
<br />
Sex: <select id='sex'>
<option value="m">m</option>
<option value="f">f</option>
</select>
<input type='button' onclick='ajaxFunction()' value='Query MySQL'/>
</form>
<div id='ajaxDiv'>Your result will display here</div>
</body>
</html>
NOTE: The way of passing variables in the Query is according to HTTP standard
and have formA.
URL?variable1=value1;&variable2=value2;
The above code will give you a screen as given below:

Ajax
19
Max Age:
Max WPM:
Sex:
Your result will display here in this section after you have made your
entry.
NOTE: This is a dummy screen.
ServerSidePHPFile
Your client-side script is ready. Now, we have to write our server-side script,
which will fetch age, wpm, and sex from the database and will send it back to
the client. Put the following code into the file "ajax-example.php".
<?php
$dbhost = "localhost";
$dbuser = "dbusername";
$dbpass = "dbpassword";
$dbname = "dbname";
//Connect to MySQL Server
mysql_connect($dbhost, $dbuser, $dbpass);
//Select Database
mysql_select_db($dbname) or die(mysql_error());
// Retrieve data from Query String
$age = $_GET['age'];
$sex = $_GET['sex'];
$wpm = $_GET['wpm'];
// Escape User Input to help prevent SQL Injection

Ajax
20
$age = mysql_real_escape_string($age);
$sex = mysql_real_escape_string($sex);
$wpm = mysql_real_escape_string($wpm);
//build query
$query = "SELECT * FROM ajax_example WHERE sex = '$sex'";
if(is_numeric($age))
$query .= " AND age <= $age";
if(is_numeric($wpm))
$query .= " AND wpm <= $wpm";
//Execute query
$qry_result = mysql_query($query) or die(mysql_error());
//Build Result String
$display_string = "<table>";
$display_string .= "<tr>";
$display_string .= "<th>Name</th>";
$display_string .= "<th>Age</th>";
$display_string .= "<th>Sex</th>";
$display_string .= "<th>WPM</th>";
$display_string .= "</tr>";
// Insert a new row in the table for each person returned
while($row = mysql_fetch_array($qry_result)){
$display_string .= "<tr>";
$display_string .= "<td>$row[name]</td>";
$display_string .= "<td>$row[age]</td>";
$display_string .= "<td>$row[sex]</td>";
$display_string .= "<td>$row[wpm]</td>";
$display_string .= "</tr>";
}
echo "Query: " . $query . "<br />";

Ajax
21
$display_string .= "</table>";
echo $display_string;
?>
Now try by entering a valid value (e.g., 120) in Max Age or any other box and
then click Query MySQL button.
Max Age:
Max WPM:
Sex:
Your result will display here in this section after you have made your
entry.
If you have successfully completed this lesson, then you know how to use
MySQL, PHP, HTML, and Javascript in tandem to write AJAX applications.

Ajax
22
AJAXSecurity:ServerSide
 AJAX-based Web applications use the same server-side security schemes
of regular Web applications.
 You specify authentication, authorization, and data protection
requirements in your web.xml file (declarative) or in your program
(programmatic).
 AJAX-based Web applications are subject to the same security threats as
regular Web applications.
AJAXSecurity:ClientSide
 JavaScript code is visible to a user/hacker. Hacker can use JavaScript
code for inferring server-side weaknesses.
 JavaScript code is downloaded from the server and executed ("eval") at
the client and can compromise the client by mal-intended code.
 Downloaded JavaScript code is constrained by the sand-box security
model and can be relaxed for signed JavaScript.
8. SECURITY

Ajax
23
AJAX is growing very fast and that is the reason that it contains many issues
with it. We hope with the passes of time, they will be resolved and AJAX will
become ideal for web applications. We are listing down a few issues that AJAX
currently suffers from.
Complexity is increased
 Server-side developers will need to understand that presentation logic will
be required in the HTML client pages as well as in the server-side logic.
 Page developers must have JavaScript technology skills.
AJAX-based applications can be difficult to debug, test, and maintain
 JavaScript is hard to test - automatic testing is hard.
 Weak modularity in JavaScript.
 Lack of design patterns or best practice guidelines yet.
Toolkits/Frameworks are not mature yet
 Most of them are in beta phase.
No standardization of the XMLHttpRequest yet
 Future version of IE will address this.
No support of XMLHttpRequest in old browsers
 Iframe will help.
JavaScript technology dependency and incompatibility
 Must be enabled for applications to function.
 Still some browser incompatibilities exist.
JavaScript code is visible to a hacker
 Poorly designed JavaScript code can invite security problems.
9. CURRENT ISSUES

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