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.

Before continuing one should have basic understanding of the following:

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.
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.

How AJAX Works

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)

Note: 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.

AJAX Example:

To understand how AJAX works, we will create a small AJAX application:

<html>

<head>

function loadXMLDoc()

{

var xmlhttp;

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("myDiv").innerHTML=xmlhttp.responseText;

}

xmlhttp.open("GET","ajax_info.txt",true);

xmlhttp.send();

}

</script>

</head>

<body>

<div id="myDiv"><h2>Let AJAX change this text</h2></div>

<button type="button" onclick="loadXMLDoc()">Change Content</button>

</body>

</html>

AJAX Example Explained

The AJAX application above contains one div section and one button.
The div section will be used to display information returned from a server. The button calls a function named loadXMLDoc(), if it is clicked:

<html>
<body>

<div id="myDiv"><h2>Let AJAX change this text</h2></div>
<button type="button" onclick="loadXMLDoc()">Change Content</button>

</body>
</html>

Next, add a <script> tag to the page's head section. The script section contains the loadXMLDoc() function:

<head>
<script type="text/javascript">
function loadXMLDoc()
{
.... AJAX script goes here ...
}
</script>
</head>

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:

variable=new XMLHttpRequest();

Old versions of Internet Explorer (IE5 and IE6) uses an ActiveX Object:

variable=new ActiveXObject("Microsoft.XMLHTTP");

To handle all modern browsers, including IE5 and IE6, check if the browser supports the XMLHttpRequest object. If it does, create an XMLHttpRequest object, if not, create an ActiveXObject:

var xmlhttp;
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}

Now we will learn about sending server requests.

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();

Method	Description
open(method,url,async)	Specifies the type of request, the URL, and if the request should be handled asynchronously or not. method: the type of request: GET or POST url: the location of the file on the server async: true (asynchronous) or false (synchronous)
send(string)	Sends the request off to the server. string: Only used for POST requests

GET or POST?

GET is simpler and faster than POST, and can be used in most cases.
However, always use POST requests when:

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","demo_get.asp",true);
xmlhttp.send();

In the example above, you may get a cached result.
To avoid this, add a unique ID to the URL:

xmlhttp.open("GET","demo_get.asp?t=" + Math.random(),true);
xmlhttp.send();

If you want to send information with the GET method, add the information to the URL:

xmlhttp.open("GET","demo_get2.asp?fname=Henry&lname=Ford",true);
xmlhttp.send();

POST Requests

A simple POST request:

xmlhttp.open("POST","demo_post.asp",true);
xmlhttp.send();

To POST data like an HTML form, add an HTTP header with setRequestHeader(). Specify the data you want to send in the send() method:

xmlhttp.open("POST","ajax_test.asp",true);
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xmlhttp.send("fname=Henry&lname=Ford");

Method	Description
setRequestHeader(header,value)	Adds HTTP headers to the request. header: specifies the header name value: specifies the header value

The url - A File On a Server

The url parameter of the open() method, is an address to a file on a server:

xmlhttp.open("GET","ajax_test.asp",true);

The file can be any kind of file, like .txt and .xml, or server scripting files like .asp and .php (which can perform actions on the server before sending the response back).

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:

xmlhttp.open("GET","ajax_test.asp",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:

execute other scripts while waiting for server response
deal with the response when the response is 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;
    }
}

We will learn more about onreadystatechange later

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:

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: Lets say the server responded with an XML file called cd_catalog.xml and lets say the contents of the XML file are as follows:

<?xml version="1.0" encoding="ISO-8859-1"?>

<!-- Edited by XMLSpy® -->

<CATALOG>

        <CD>

               <TITLE>Empire Burlesque</TITLE>

               <ARTIST>Bob Dylan</ARTIST>

               <COUNTRY>USA</COUNTRY>

               <COMPANY>Columbia</COMPANY>

               <PRICE>10.90</PRICE>

               <YEAR>1985</YEAR>

        </CD>

        <CD>

               <TITLE>Hide your heart</TITLE>

               <ARTIST>Bonnie Tyler</ARTIST>

               <COUNTRY>UK</COUNTRY>

               <COMPANY>CBS Records</COMPANY>

               <PRICE>9.90</PRICE>

               <YEAR>1988</YEAR>

        </CD>

        <CD>

               <TITLE>Greatest Hits</TITLE>

               <ARTIST>Dolly Parton</ARTIST>

               <COUNTRY>USA</COUNTRY>

               <COMPANY>RCA</COMPANY>

               <PRICE>9.90</PRICE>

               <YEAR>1982</YEAR>

        </CD>

        <CD>

               <TITLE>Still got the blues</TITLE>

               <ARTIST>Gary Moore</ARTIST>

               <COUNTRY>UK</COUNTRY>

               <COMPANY>Virgin records</COMPANY>

               <PRICE>10.20</PRICE>

               <YEAR>1990</YEAR>

        </CD>

        <CD>

               <TITLE>Eros</TITLE>

               <ARTIST>Eros Ramazzotti</ARTIST>

               <COUNTRY>EU</COUNTRY>

               <COMPANY>BMG</COMPANY>

               <PRICE>9.90</PRICE>

               <YEAR>1997</YEAR>

        </CD>

        <CD>

               <TITLE>One night only</TITLE>

               <ARTIST>Bee Gees</ARTIST>

               <COUNTRY>UK</COUNTRY>

               <COMPANY>Polydor</COMPANY>

               <PRICE>10.90</PRICE>

               <YEAR>1998</YEAR>

        </CD>

        <CD>

               <TITLE>Sylvias Mother</TITLE>

               <ARTIST>Dr.Hook</ARTIST>

               <COUNTRY>UK</COUNTRY>

               <COMPANY>CBS</COMPANY>

               <PRICE>8.10</PRICE>

               <YEAR>1973</YEAR>

        </CD>

        <CD>

               <TITLE>Maggie May</TITLE>

               <ARTIST>Rod Stewart</ARTIST>

               <COUNTRY>UK</COUNTRY>

               <COMPANY>Pickwick</COMPANY>

               <PRICE>8.50</PRICE>

               <YEAR>1990</YEAR>

        </CD>

        <CD>

               <TITLE>Midt om natten</TITLE>

               <ARTIST>Kim Larsen</ARTIST>

               <COUNTRY>EU</COUNTRY>

               <COMPANY>Medley</COMPANY>

               <PRICE>7.80</PRICE>

               <YEAR>1983</YEAR>

        </CD>

</CATALOG>

Request the file cd_catalog.xml and parse the response:

xmlDoc=xmlhttp.responseXML;
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;

Example

<html>

<head>

function loadXMLDoc()

{

var xmlhttp;

var txt,x,i;

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)

{

xmlDoc=xmlhttp.responseXML;

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;

}

xmlhttp.open("GET","cd_catalog.xml",true);

xmlhttp.send();

}

</script>

</head>

<body>

<h2>My CD Collection:</h2>

<button type="button" onclick="loadXMLDoc()">Get my CD collection</button>

</body>

</html>

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:

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.

Using a Callback Function

A callback function is a function passed as a parameter to another function.

If you have more than one AJAX task on your website, you should create ONE standard function for creating the XMLHttpRequest object, and call this for each AJAX task.

The function call should contain the URL and what to do on onreadystatechange (which is probably different for each call):

Example:

<html>

<head>

var xmlhttp;

function loadXMLDoc(url,cfunc)

{

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=cfunc;

xmlhttp.open("GET",url,true);

xmlhttp.send();

}

function myFunction()

{

loadXMLDoc("ajax_info.txt",function()

{

if (xmlhttp.readyState==4 && xmlhttp.status==200)

{

document.getElementById("myDiv").innerHTML=xmlhttp.responseText;

}

});

}

</script>

</head>

<body>

<div id="myDiv"><h2>Let AJAX change this text</h2></div>

<button type="button" onclick="myFunction()">Change Content</button>

</body>

</html>

AJAX ASP/JSP/PHP Example

AJAX is used to create more interactive applications.

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:

<html>

<head>

function showHint(str)

{

var xmlhttp;

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.jsp?q="+str,true);

xmlhttp.send();

}

</script>

</head>

<body>

<h3>Start typing a name in the input field below:</h3>

First name: <input type="text" id="txt1" onkeyup="showHint(this.value)" />

</form>

<p>Suggestions: <span id="txtHint"></span></p>

</body>

</html>

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:

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)

For creating this using jsp and java we can do following:

We can have a DummyDB.java file.

package user.autocomplete;

import java.util.ArrayList;

import java.util.List;

import java.util.StringTokenizer;

public class DummyDB {

private int totalCountries;

private String data = "Afghanistan, Albania, Zimbabwe, India, Sri Lanka, Japan";

private List<String> countries;

public DummyDB() {

countries = new ArrayList<String>();

StringTokenizer st = new StringTokenizer(data, ",");

while(st.hasMoreTokens()) {

countries.add(st.nextToken().trim());

}

totalCountries = countries.size();

}

public List<String> getData(String query) {

String country = null;

query = query.toLowerCase();

List<String> matched = new ArrayList<String>();

for(int i=0; i<totalCountries; i++) {

country = countries.get(i).toLowerCase();

if(country.startsWith(query)) {

matched.add(countries.get(i));

}

return matched;

}

Here we are using a dummy list of countries. The function getData(query) returns a filtered list based on the query. If we are not using a dummyDB and if we are using a dbms then we can run a SQL statement in the getData(query) method. Following SQL statement will do the work:

“Select countries from <table> where countries like ”+query+”%”;

Now gethint.jsp

<%@page import="java.util.Iterator"%>

<%@page import="java.util.List"%>

<%@page import="user.DummyDB"%>

DummyDB db = new DummyDB();

String query = request.getParameter("q");

List<String> countries = db.getData(query);

Iterator<String> iterator = countries.iterator();

while(iterator.hasNext()) {

String country = (String)iterator.next();

out.println(country);

}

AJAX Database Example

AJAX can be used for interactive communication with a database.

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

<html>

<head>

function showCustomer(str)

{

var xmlhttp;

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.jsp?q="+str,true);

xmlhttp.send();

}

</script>

</head>

<body>

<option value="">Select a customer:</option>

<option value="ALFKI">Alfreds Futterkiste</option>

<option value="NORTS ">North/South</option>

<option value="WOLZA">Wolski Zajazd</option>

</select>

</form>

<br />

<div id="txtHint">Customer info will be listed here...</div>

</body>

</html>

The showCustomer() function does the following:

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)

getcustomer.jsp page would look something like this:

<%
//Step1: Load JDBC Driver
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
//Step 2: Establish connection to URL
Connection conn = DriverManager.getConnection("connection URL”);
//Step 3: Create Statement object
Statement stmt = conn.createStatement();
//Step 4: Execute SQL command
String sqlStr = "SELECT * FROM CUSTOMERS WHERE CUSTOMERID="+request.getParameter(“q”);
ResultSet rst = stmt.executeQuery(sqlStr);
//Step 5:Process the results (from database)
while(rst.next())
{
%>

<table border="1">
<tr>
<td>CustomerID:</td>
<td>
<%=rst.getString("CustomerID ")%>
</td>
</tr>
<tr>
<td>Customer Name</td>
<td>
<%=rst.getString("CustomerName")%>
</td>
</tr>
<tr>
<td>Contact Number:</td>
<td>

<%=rst.getString("ContactNo")%>

</td>
</tr>
<tr>
<td>Address</td>
<td>

<%=rst.getString("Address")%>
</td>
</tr>
</table>

<%}/*end while*/

//Step 6:Close connection
rst.close();
stmt.close();
conn.close();
%>

</body>
</html>

AJAX XML Example

AJAX can be used for interactive communication with an XML file. The following example will demonstrate how a web page can fetch information from an XML file with AJAX:

<html>

<head>

function loadXMLDoc(url)

{

var xmlhttp;

var txt,x,xx,i;

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)

{

txt="<table border='1'><tr><th>Title</th><th>Artist</th></tr>";

x=xmlhttp.responseXML.documentElement.getElementsByTagName("CD");

for (i=0;i<x.length;i++)

{

txt=txt + "<tr>";

xx=x[i].getElementsByTagName("TITLE");

{

try

{

txt=txt + "<td>" + xx[0].firstChild.nodeValue + "</td>";

}

catch (er)

{

txt=txt + "<td> </td>";

}

xx=x[i].getElementsByTagName("ARTIST");

{

try

{

txt=txt + "<td>" + xx[0].firstChild.nodeValue + "</td>";

}

catch (er)

{

txt=txt + "<td> </td>";

}

txt=txt + "</tr>";

}

txt=txt + "</table>";

document.getElementById('txtCDInfo').innerHTML=txt;

}

xmlhttp.open("GET",url,true);

xmlhttp.send();

}

</script>

</head>

<body>

</div>

</body>

</html>

Example Explained - The stateChange() Function

When a user clicks on the "Get CD info" button above, the loadXMLDoc() function is executed.
The loadXMLDoc() function creates an XMLHttpRequest object, adds the function to be executed when the server response is ready, and sends the request off to the server.
When the server response is ready, an HTML table is built, nodes (elements) are extracted from the XML file, and it finally updates the txtCDInfo placeholder with the HTML table filled with XML data:

The AJAX Server Page

The page on the server used in the example above, is an XML file called "cd_catalog.xml".

AJAX Examples

A simple AJAX example:
Create a simple XMLHttpRequest, and retrieve data from a TXT file.

<html>

<head>

function loadXMLDoc()

{

var xmlhttp;

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("myDiv").innerHTML=xmlhttp.responseText;

}

xmlhttp.open("GET","ajax_info.txt",true);

xmlhttp.send();

}

</script>

</head>

<body>

<div id="myDiv"><h2>Let AJAX change this text</h2></div>

<button type="button" onclick="loadXMLDoc()">Change Content</button>

</body>

</html>

Retrieve header information with AJAX

Retrieve header information of a resource (file).

<html>

<head>

function loadXMLDoc(url)

{

var xmlhttp;

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('p1').innerHTML=xmlhttp.getAllResponseHeaders();

}

xmlhttp.open("GET",url,true);

xmlhttp.send();

}

</script>

</head>

<body>

<p id="p1">The getAllResponseHeaders() function returns the header information of a resource, like length, server-type, content-type, last-modified, etc.</p>

<button onclick="loadXMLDoc('ajax_info.txt')">Get header information</button>

</body>

</html>

Retrieve specific header information with AJAX

Retrieve header information of a resource (file).

<html>

<head>

function loadXMLDoc(url)

{

var xmlhttp;

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('p1').innerHTML="Last modified: " + xmlhttp.getResponseHeader('Last-Modified');

}

xmlhttp.open("GET",url,true);

xmlhttp.send();

}

</script>

</head>

<body>

<p id="p1">The getResponseHeader() function is used to return specific header information from a resource, like length, server-type, content-type, last-modified, etc.</p>

<button onclick="loadXMLDoc('ajax_info.txt')">Get "Last-Modified" information</button>

</body>

</html>

AJAX

Wednesday, 23 March 2011

Introduction to AJAX

What is AJAX?

How AJAX Works

AJAX is Based on Internet Standards

Google Suggest

AJAX Example Explained

AJAX - Create an XMLHttpRequest Object

The XMLHttpRequest Object

Create an XMLHttpRequest Object

Send a Request to a Server

GET or POST?

GET Requests

POST Requests

The url - A File On a Server

Asynchronous - True or False?

Async=true

Async=false

AJAX - Server Response

Server Response

The responseText Property

The responseXML Property

AJAX - The onreadystatechange Event

The onreadystatechange event

Using a Callback Function

AJAX ASP/JSP/PHP Example

Example Explained - The showHint() Function

AJAX Database Example

AJAX XML Example

Example Explained - The stateChange() Function

The AJAX Server Page

No comments:

Post a Comment