AJAX Tuturial

8/8/2019 AJAX Tuturial

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AJAX Tutorial

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AJAX = Asynchronous JavaScript and XML.

AJAX is not a new programming language, but a new way to useexisting standards.

AJAX is the art of exchanging data with a server, and updateparts of a web page - without reloading the whole page.

AJAX Example

Let AJAX change this textChange Content

Try it yourself

Start learning AJAX now!

AJAX Introduction

Previous Next Chapter

AJAX is about updating parts of a web page, without reloading the whole page.

What You Should Already Know

Before you continue you should have a basic understanding of the following:

HTML / XHTML

CSS

JavaScript / DOM

If you want to study these subjects first, find the tutorials on our Home page.

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 theserver behind the scenes. This means that it is possible to update parts of a web page, withoutreloading the whole page.
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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.

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)

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 inGoogle's search box, a JavaScript sends the letters off to a server and the server returns a list ofsuggestions.

Start Using AJAX Today

AJAX is based on existing standards. These standards have been used by developers for several years.Read our next chapters to see how it works!
http://www.google.com/http://www.google.com/


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AJAX Example


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

Example


Try it yourself

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 functionnamed loadXMLDoc(), if it is clicked:


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

function loadXMLDoc(){.... AJAX script goes here ...}

The next chapters will explain how AJAX works.


AJAX - Create an XMLHttpRequest Object

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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 meansthat 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 XMLHttpRequestobject.

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");

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

Example

if (window.XMLHttpRequest){// code for IE7+, Firefox, Chrome, Opera, Safarixmlhttp=new XMLHttpRequest();}

else{// code for IE6, IE5

xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}

Try it yourself

In the next chapter you will learn about sending server requests.


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);
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xmlhttp.send();

Method Description

open(method,url,async) Specifies the type of request, the URL, and if the request should behandled asynchronously or not.

method: the type of request: GET or POSTurl: the location of the file on the serverasync: 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 securethan GET

GET Requests

A simple GET request:

Example

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

Try it yourself

In the example above, you may get a cached result.

To avoid this, add a unique ID to the URL:

Example

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

Try it yourself

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

Example

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

POST RequestsA simple POST request:

Example

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

Try it yourself

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

Example

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

Try it yourself

Method Description

setRequestHeader(header,value) Adds HTTP headers to the request.

header: specifies the header namevalue: 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 canperform 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 asAJAX, the async parameter of the open() method has to be set to true:

xmlhttp.open("GET","ajax_test.asp",true);
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Sending asynchronously requests is a huge improvement for web developers. Many of the tasksperformed on the server are very time consuming. Before AJAX, this operation could cause theapplication 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 ready

Async=true

When using async=true, specify a function to execute when the response is ready in theonreadystatechange event:

Example

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();

Try it yourself

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 theserver 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 codeafter the send() statement:

Example

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

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

Try it yourself


AJAX - Server Response
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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;

Try it yourself

The responseXML Property

If the response from the server is XML, and you want to parse it as an XML object, use theresponseXML 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


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Three important properties of the XMLHttpRequest object:

Property Description

onreadystatechange

Stores a function (or the name of a function) to be called automatically eachtime the readyState property changes

readyState Holds the status of the XMLHttpRequest. Changes from 0 to 4:

0: request not initialized1: server connection established2: request received3: processing request4: 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 tobe 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;}

}

Try it yourself

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 forcreating 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 probablydifferent for each call):

Example

function myFunction(){

loadXMLDoc("ajax_info.txt",function(){if (xmlhttp.readyState==4 && xmlhttp.status==200){document.getElementById("myDiv").innerHTML=xmlhttp.responseText;}

});}
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Try it yourself


AJAX ASP/PHP Example Previous Next Chapter

AJAX is used to create more interactive applications.

AJAX ASP/PHP Example

The following example will demonstrate how a web page can communicate with a web server while auser type characters in an input field:

Example

Start typing a name in the input field below:

Top of Form

First name:Bottom of Form

Suggestions:

Try it yourself

Example Explained - The showHint() Function

When a user types a character in the input field above, the function "showHint()" is executed. Thefunction 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, Safarixmlhttp=new XMLHttpRequest();}

else{// code for IE6, IE5xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}

xmlhttp.onreadystatechange=function(){
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if (xmlhttp.readyState==4 && xmlhttp.status==200){document.getElementById("txtHint").innerHTML=xmlhttp.responseText;}

}xmlhttp.open("GET","gethint.asp?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 placeholderand 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 AJAX Server Page - ASP and PHP

The page on the server called by the JavaScript above is an ASP file called "gethint.asp".

Below we have created two versions of the server file, one written in ASP and one in PHP.

The ASP File

The source code in "gethint.asp" checks an array of names, and returns the corresponding name(s) tothe browser:


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a(20)="Eve"a(21)="Evita"a(22)="Sunniva"a(23)="Tove"a(24)="Unni"a(25)="Violet"

a(26)="Liza"a(27)="Elizabeth"a(28)="Ellen"a(29)="Wenche"a(30)="Vicky"

'get the q parameter from URLq=ucase(request.querystring("q"))

'lookup all hints from array if length of q>0if len(q)>0 thenhint=""for i=1 to 30if q=ucase(mid(a(i),1,len(q))) then

if hint="" thenhint=a(i)

elsehint=hint & " , " & a(i)

end ifend if

nextend if

'Output "no suggestion" if no hint were found'or output the correct valuesif hint="" thenresponse.write("no suggestion")

elseresponse.write(hint)end if%>

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".


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$a[]="Inga";$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>0if (strlen($q) > 0){$hint="";for($i=0; $i


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//output the responseecho $response;?>


AJAX Database Example


AJAX can be used for interactive communication with a database.

AJAX Database Example

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

Example

Top of Form

Bottom of Form

Customer info will be listed here...

Try it yourself

Example Explained - The showCustomer() Function

When a user selects a customer in the dropdown list above, a function called "showCustomer()" isexecuted. The function is triggered by the "onchange" event:

function showCustomer(str){if (str==""){document.getElementById("txtHint").innerHTML="";return;}

if (window.XMLHttpRequest)

{// code for IE7+, Firefox, Chrome, Opera, Safarixmlhttp=new XMLHttpRequest();}

else{// code for IE6, IE5xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}

xmlhttp.onreadystatechange=function(){
http://www.w3schools.com/Ajax/ajax_xmlhttprequest_onreadystatechange.asphttp://www.w3schools.com/Ajax/ajax_database.asphttp://www.w3schools.com/Ajax/ajax_aspphp.asphttp://www.w3schools.com/Ajax/ajax_xmlfile.asphttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_databasehttp://www.w3schools.com/Ajax/ajax_xmlhttprequest_onreadystatechange.asphttp://www.w3schools.com/Ajax/ajax_database.asphttp://www.w3schools.com/Ajax/ajax_aspphp.asphttp://www.w3schools.com/Ajax/ajax_xmlfile.asphttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_database


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if (xmlhttp.readyState==4 && xmlhttp.status==200){document.getElementById("txtHint").innerHTML=xmlhttp.responseText;}

}xmlhttp.open("GET","getcustomer.asp?q="+str,true);

xmlhttp.send();}

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)

The AJAX Server PageThe page on the server called by the JavaScript above is an ASP file called "getcustomer.asp".

The server file could easily be rewritten in PHP, or some other server languages.Look at acorresponding example in PHP.

The source code in "getcustomer.asp" runs a query against a database, and returns the result in anHTML table:


AJAX XML Example

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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

Get CD info

Try it yourself

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 whenthe 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 theXML file, and it finally updates the txtCDInfo placeholder with the HTML table filled with XML data:

function loadXMLDoc(url){if (window.XMLHttpRequest){// code for IE7+, Firefox, Chrome, Opera, Safarixmlhttp=new XMLHttpRequest();}

else{// code for IE6, IE5

xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}xmlhttp.onreadystatechange=function(){if (xmlhttp.readyState==4 && xmlhttp.status==200){txt="TitleArtist";x=xmlhttp.responseXML.documentElement.getElementsByTagName("CD");for (i=0;i


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{try{txt=txt + "" + xx[0].firstChild.nodeValue + "";}

catch (er)

{txt=txt + "";}

}txt=txt + "";}

txt=txt + "";document.getElementById('txtCDInfo').innerHTML=txt;}

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

The AJAX Server Page

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


AJAX Examples


Try it Yourself - Examples

A simple AJAX exampleCreate a simple XMLHttpRequest, and retrieve data from a TXT file.

function loadXMLDoc()

{


{// code for IE7+, Firefox, Chrome, Opera, Safari


}

else
http://www.w3schools.com/Ajax/cd_catalog.xmlhttp://www.w3schools.com/Ajax/ajax_database.asphttp://www.w3schools.com/Ajax/ajax_examples.asphttp://www.w3schools.com/Ajax/ajax_xmlfile.asphttp://www.w3schools.com/Ajax/default.asphttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_firsthttp://www.w3schools.com/Ajax/cd_catalog.xmlhttp://www.w3schools.com/Ajax/ajax_database.asphttp://www.w3schools.com/Ajax/ajax_examples.asphttp://www.w3schools.com/Ajax/ajax_xmlfile.asphttp://www.w3schools.com/Ajax/default.asphttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_first


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{// code for IE6, IE5


}

xmlhttp.onreadystatechange=function()

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

{


}

}

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

xmlhttp.send();

}

Let AJAX change this text

Change Content


Change Content

AJAX is not a new programming language.


Change Content

Load an XML file with AJAXCreate an XMLHttpRequest to retrieve data from an XML file.

function loadXMLDoc(url)

{


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}

else



}


{

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

{

document.getElementById('A1').innerHTML=xmlhttp.status;

document.getElementById('A2').innerHTML=xmlhttp.statusText;

document.getElementById('A3').innerHTML=xmlhttp.responseText;

}

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

xmlhttp.send();

}

Retrieve data from XML file

Status:

Status text:

Response:

Get XML data


Status:

Status text:

Response:

Get XML data


Status:200

Status text:OK


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Response: Tove Jani Reminder Don't forget me this weekend!

Get XML data

Retrieve header information with AJAXRetrieve header information of a resource (file).


{




}

else

{// code for IE6, IE5xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");

}


{


{

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

}

}

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

xmlhttp.send();

}

The getAllResponseHeaders() function returns the header information of a resource, likelength, server-type, content-type, last-modified, etc.

Get header information

The getAllResponseHeaders() function returns the header information of a resource,like length, server-type, content-type, last-modified, etc.

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Date: Wed, 20 Oct 2010 08:01:00 GMT X-Powered-By: ASP.NETMicrosoftOfficeWebServer: 5.0_Pub Content-Length: 115 Last-Modified: Mon, 19Apr 2010 12:15:17 GMT Server: Microsoft-IIS/6.0 ETag: "7ce5df9b9dfca1:4cd"Content-Type: text/plain Accept-Ranges: bytes


Retrieve specific header information with AJAXRetrieve specific header information of a resource (file).


{



xmlhttp=new XMLHttpRequest();}

else



}


{


{

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

}

}


xmlhttp.send();

}

The getResponseHeader() function is used to return specific header information from aresource, like length, server-type, content-type, last-modified, etc.

Get "Last-Modified" information
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The getResponseHeader() function is used to return specific header information froma resource, like length, server-type, content-type, last-modified, etc.

Get "Last-Modified" information

Last modified: Mon, 19 Apr 2010 12:15:17 GMT

Get "Last-Modified" informationRetrieve the content of an ASP fileHow a web page can communicate with a web server while a user type characters in an input field.

function showHint(str)

{

if (str.length==0)

{

document.getElementById("txtHint").innerHTML="";

return;

}




}

else


xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}


{


{

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

}

}

xmlhttp.open("GET","gethint.asp?q="+str,true);

xmlhttp.send();

}

Start typing a name in the input field below:
http://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_suggesthttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_suggest


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First name:

Suggestions:

Start typing a name in the input field below:Top of Form

First name:

Bottom of Form

Suggestions:

Start typing a name in the input field below:Top of Form

First name:

Bottom of Form

Suggestions: no suggestion

Retrieve content from a databaseHow a web page can fetch information from a database with AJAX.

function showCustomer(str)

{

if (str=="")

{

document.getElementById("txtHint").innerHTML="";

return;

}




}

else


http://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_databasehttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_database


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}


{


{

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

}

}

xmlhttp.open("GET","getcustomer.asp?q="+str,true);

xmlhttp.send();

}

Select a customer:

Alfreds Futterkiste

North/South

Wolski Zajazd

Customer info will be listed here...

Top of Form

Alfreds Futterkiste

Bottom of Form

Customer info will be listed here...Top of Form

Bottom of Form

CustomerID ALFKI

CompanyName Alfreds Futterkiste

ContactName Maria Anders


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Address Obere Str. 57

City Berlin

PostalCode 12209

Country Germany

Retrieve the content of an XML fileCreate an XMLHttpRequest to retrieve data from an XML file and display the data in an HTML table.


{




}

else



}


{


{

txt="TitleArtist";

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

for (i=0;i


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{

try

{

txt=txt + "" + xx[0].firstChild.nodeValue + "";

}

catch (er)

{

txt=txt + " ";

}

}

txt=txt + "";

}

txt=txt + "";

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

}}


xmlhttp.send();

}

Get CD info

Get CD info

TitleArtistEmpire BurlesqueBob DylanHide your heartBonnieTylerGreatest HitsDolly PartonStill got the bluesGary MooreErosErosRamazzottiOne night onlyBee GeesSylvias MotherDr.HookMaggie

MayRod StewartRomanzaAndrea BocelliWhen a man loves awomanPercy SledgeBlack angelSavage Rose1999 GrammyNomineesManyFor the good timesKenny RogersBig Willie styleWillSmithTupelo HoneyVan MorrisonSoulsvilleJorn HoelThe very bestofCat StevensStopSam BrownBridge of SpiesT'PauPrivateDancerTina TurnerMidt om nattenKim LarsenPavarotti Gala


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ConcertLuciano PavarottiThe dock of the bayOtis ReddingPicturebookSimply RedRedThe CommunardsUnchain my heartJoe Cocker

An AJAX example with a callback functionCreate a XMLHttpRequest with a callback function, and retrieve data from a TXT file.

function loadXMLDoc(url,cfunc)

{




}

else

{// code for IE6, IE5xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");

}

xmlhttp.onreadystatechange=cfunc;


xmlhttp.send();

}

function myFunction()

{

loadXMLDoc("ajax_info.txt",function()

{


{


}

});

}


Change Content
http://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_callbackhttp://www.w3schools.com/Ajax/tryit.asp?filename=tryajax_callback


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Change Content

AJAX is not a new programming language.


Change Content

http://www.w3schools.com/Ajax/ajax_xmlfile.asphttp://www.w3schools.com/Ajax/default.asphttp://www.w3schools.com/Ajax/ajax_xmlfile.asphttp://www.w3schools.com/Ajax/default.asp

AJAX Tuturial

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Transcript of AJAX Tuturial