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					AJAX = Asynchronous JavaScript And XML AJAX is an acronym for Asynchronous JavaScript And XML.> AJAX is not a new programming language, but simply a new technique for creating better, faster, and more interactive web applications. AJAX uses JavaScript to send and receive data between a web browser and a web server. The AJAX technique makes web pages more responsive by exchanging data with the web server behind the scenes, instead of reloading an entire web page each time a user makes a change. AJAX Is A Browser Technology AJAX is a technology that runs in your browser. It uses asynchronous data transfer (HTTP requests) between the browser and the web server, allowing web pages to request small bits of information from the server instead of whole pages. The technology makes Internet applications smaller, faster and more user friendly. AJAX is a web browser technology independent of web server software. AJAX Is Based On Open Standards AJAX is based on the following open standards:

   

JavaScript XML HTML CSS

The open standards used in AJAX are well defined, and supported by all major browsers. AJAX applications are browser and platform independent. (Cross-Platform, Cross-Browser technology) AJAX Is About Better Internet Applications Web applications have many benefits over desktop applications, they can reach a larger audience, they are easier to install and support, and easier to develop. However, Internet applications are not always as "rich" and user-friendly as traditional desktop applications. With AJAX, Internet applications can be made richer (smaller, faster, and easier to use). You Can Start Using AJAX Today There is nothing new to learn. AJAX is based on open standards. These standards have been used by most developers for several years. Most existing web applications can be rewritten to use AJAX technology instead of traditional HTML forms.

AJAX Uses XML And HTTP Requests In traditional JavaScript coding, if you want to get any information from a database or a file on the server, or send user information to a server, you will have to make an HTML form and GET or POST data to the server. The user will have to click the "Submit" button to send/get the information, wait for the server to respond, then a new page will load with the results. Because the server returns a new page each time the user submits input, traditional web applications can run slowly and tend to be less user-friendly. With AJAX, your JavaScript communicates directly with the server, through the JavaScript XMLHttpRequest object With an HTTP request, a web page can make a request to, and get a response from a web server - without reloading the page. The user will stay on the same page, and he or she will not notice that scripts request pages, or send data to a server in the background.

The XMLHttpRequest Object By using the XMLHttpRequest object, a web developer can update a page with data from the server after the page has loaded! AJAX was made popular in 2005 by Google (with Google Suggest). Google Suggest is using the XMLHttpRequest object 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. The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 8+, and Netscape 7.

Your First AJAX Application To understand how AJAX works, we will create a small AJAX application. First, we are going to create a standard HTML form with two text fields: username and time. The username field will be filled in by the user and the time field will be filled in using AJAX. The HTML file will be named "testAjax.htm", and it looks like this (notice that the HTML form below has no submit button!): <html> <body> <form name="myForm"> Name: <input type="text" name="username" /> Time: <input type="text" name="time" /> </form> </body>

</html> The next chapters will explain the keystones of AJAX. AJAX - Browser Support The keystone of AJAX is the XMLHttpRequest object. Different browsers use different methods to create the XMLHttpRequest object. Internet Explorer uses an ActiveXObject, while other browsers uses the built-in JavaScript object called XMLHttpRequest. To create this object, and deal with different browsers, we are going to use a "try and catch" statement. You can read more about the try and catch statement in our JavaScript tutorial. Let's update our "testAjax.htm" file with the JavaScript that creates the XMLHttpRequest object: <html> <body> <script type="text/javascript"> function ajaxFunction() { var xmlHttp; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e) { // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) { alert("Your browser does not support AJAX!"); return false; } } } } </script> <form name="myForm"> Name: <input type="text" name="username" /> Time: <input type="text" name="time" /> </form> </body> </html>

Example explained: First create a variable xmlHttp to hold the XMLHttpRequest object. Then try to create the object with XMLHttp=new XMLHttpRequest(). This is for the Firefox, Opera, and Safari browsers. If that fails, try xmlHttp=new ActiveXObject("Msxml2.XMLHTTP") which is for Internet Explorer 6.0+, if that also fails, try xmlHttp=new ActiveXObject("Microsoft.XMLHTTP") which is for Internet Explorer 5.5+ If none of the three methods work, the user has a very outdated browser, and he or she will get an alert stating that the browser doesn't support AJAX. Note: The browser-specific code above is long and quite complex. However, this is the code you can use every time you need to create an XMLHttpRequest object, so you can just copy and paste it whenever you need it. The code above is compatible with all the popular browsers: Internet Explorer, Opera, Firefox, and Safari. The next chapter shows how to use the XMLHttpRequest object to communicate with the server. AJAX - More About the XMLHttpRequest Object Before sending data to the server, we have to explain three important properties of the XMLHttpRequest object. The onreadystatechange Property After a request to the server, we need a function that can receive the data that is returned by the server. The onreadystatechange property stores the function that will process the response from a server. The following code defines an empty function and sets the onreadystatechange property at the same time: xmlHttp.onreadystatechange=function() { // We are going to write some code here } The readyState Property The readyState property holds the status of the server's response. Each time the readyState changes, the onreadystatechange function will be executed. Here are the possible values for the readyState propery: State 0 1 2 3 4 Description The request is not initialized The request has been set up The request has been sent The request is in process The request is complete

We are going to add an If statement to the onreadystatechange function to test if our response is complete (this means that we can get our data): xmlHttp.onreadystatechange=function() { if(xmlHttp.readyState==4)

}

{ // Get the data from the server's response }

The responseText Property The data sent back from the server can be retrieved with the responseText property. In our code, we will set the value of our "time" input field equal to responseText: xmlHttp.onreadystatechange=function() { if(xmlHttp.readyState==4) { document.myForm.time.value=xmlHttp.responseText; } } The next chapter shows how to ask the server for some data! AJAX - Sending a Request to the Server To send off a request to the server, we use the open() method and the send() method. The open() method takes three arguments. The first argument defines which method to use when sending the request (GET or POST). The second argument specifies the URL of the server-side script. The third argument specifies that the request should be handled asynchronously. The send() method sends the request off to the server. If we assume that the HTML and ASP file are in the same directory, the code would be: xmlHttp.open("GET","time.asp",true); xmlHttp.send(null); Now we must decide when the AJAX function should be executed. We will let the function run "behind the scenes" when the user types something in the username text field: <form name="myForm"> Name: <input type="text" onkeydown="ajaxFunction();" name="username" /> Time: <input type="text" name="time" /> </form> Our updated AJAX-ready "testAjax.htm" file now looks like this: <html> <body> <script type="text/javascript"> function ajaxFunction() { var xmlHttp; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e)

} </script> <form name="myForm"> Name: <input type="text" onkeydown="ajaxFunction();" name="username" /> Time: <input type="text" name="time" /> </form> </body> </html>

{ // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) { alert("Your browser does not support AJAX!"); return false; } } } xmlHttp.onreadystatechange=function() { if(xmlHttp.readyState==4) { document.myForm.time.value=xmlHttp.responseText; } } xmlHttp.open("GET","time.asp",true); xmlHttp.send(null);

The next chapter makes our AJAX application complete with the "time.asp" script. AJAX - The Server-Side ASP Script Now we are going to create the script that displays the current server time. The responseText property (explained in the previous chapter) will store the data returned from the server. Here we want to send back the current time. The code in "time.asp" looks like this: <% response.write(time) %>

Run Your AJAX Application Try the AJAX application by typing some text into the Name text box below, then click inside the Time text box:

Name:

Time:

The Time text box gets the server's time from "time.asp" file without reloading the page! AJAX Suggest Example In the AJAX example below we will demonstrate how a web page can communicate with a web server online as a user enters data into a standard HTML form.

Type a Name in the Box Below First Name: Suggestions:
Raja Raman

Example Explained - The HTML Form The form above has the following HTML code: <form> First Name: <input type="text" id="txt1" onkeyup="showHint(this.value)"> </form> <p>Suggestions: <span id="txtHint"></span></p> As you can see it is just a simple HTML form with an input field called "txt1". An event attribute for the input field defines a function to be triggered by the onkeyup event. The paragraph below the form contains a span called "txtHint". The span is used as a placeholder for data retrieved from the web server. When the user inputs data, a function called "showHint()" is executed. The execution of the function is triggered by the "onkeyup" event. In other words: Each time the user moves his finger away from a keyboard key inside the input field, the function showHint is called.

Example Explained - The showHint() Function The showHint() function is a very simple JavaScript function placed in the <head> section of the HTML page. The function contains the following code: function showHint(str) { if (str.length==0) { document.getElementById("txtHint").innerHTML=""; return; } xmlHttp=GetXmlHttpObject()

if (xmlHttp==null) { alert ("Your browser does not support AJAX!"); return; } var url="gethint.asp"; url=url+"?q="+str; url=url+"&sid="+Math.random(); xmlHttp.onreadystatechange=stateChanged; xmlHttp.open("GET",url,true); xmlHttp.send(null); } The function executes every time a character is entered in the input field. If there is some input in the text field (str.length > 0) the function executes the following:

     

Defines the url (filename) to send to the server Adds a parameter (q) to the url with the content of the input field Adds a random number to prevent the server from using a cached file Creates an XMLHTTP object, and tells the object to execute a function called stateChanged when a change is triggered Opens the XMLHTTP object with the given url. Sends an HTTP request to the server

If the input field is empty, the function simply clears the content of the txtHint placeholder. The AJAX HTML Page This is the HTML page. It contains a simple HTML form and a link to a JavaScript. <html> <head> <script src="clienthint.js"></script> </head> <body> <form> First Name: <input type="text" id="txt1" onkeyup="showHint(this.value)"> </form> <p>Suggestions: <span id="txtHint"></span></p> </body> </html> The JavaScript code is listed below.

The AJAX JavaScript This is the JavaScript code, stored in the file "clienthint.js": var xmlHttp function showHint(str) { if (str.length==0)

{ document.getElementById("txtHint").innerHTML=""; return; } xmlHttp=GetXmlHttpObject() if (xmlHttp==null) { alert ("Your browser does not support AJAX!"); return; } var url="gethint.asp"; url=url+"?q="+str; url=url+"&sid="+Math.random(); xmlHttp.onreadystatechange=stateChanged; xmlHttp.open("GET",url,true); xmlHttp.send(null); } function stateChanged() { if (xmlHttp.readyState==4) { document.getElementById("txtHint").innerHTML=xmlHttp.responseText; } } function GetXmlHttpObject() { var xmlHttp=null; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e) { // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } } return xmlHttp; }

The AJAX Server Page - ASP and PHP There is no such thing as an AJAX server. AJAX pages can be served by any internet server. The server page called by the JavaScript in the example from the previous chapter is a simple ASP file called "gethint.asp". Below we have listed two examples of the server page code, one written in ASP and one in PHP.

AJAX ASP Example The code in the "gethint.asp" page is written in VBScript for an Internet Information Server (IIS). It just checks an array of names and returns the corresponding names to the client: <% dim a(30) 'Fill up array with names a(1)="Anna" a(2)="Brittany" a(3)="Cinderella" a(4)="Diana" a(5)="Eva" a(6)="Fiona" a(7)="Gunda" a(8)="Hege" a(9)="Inga" a(10)="Johanna" a(11)="Kitty" a(12)="Linda" a(13)="Nina" a(14)="Ophelia" a(15)="Petunia" a(16)="Amanda" a(17)="Raquel" a(18)="Cindy" a(19)="Doris" 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 URL q=ucase(request.querystring("q")) 'lookup all hints from array if length of q>0 if len(q)>0 then hint="" for i=1 to 30 if q=ucase(mid(a(i),1,len(q))) then if hint="" then hint=a(i) else hint=hint & " , " & a(i) end if end if next end if 'Output "no suggestion" if no hint were found 'or output the correct values if hint="" then response.write("no suggestion") else response.write(hint) end if %>

AJAX PHP Example The code above rewritten in PHP. Note: To run the entire example in PHP, remember to change the value of the url variable in "clienthint.js" from "gethint.asp" to "gethint.php". PHP Example <?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 In the AJAX example below we will demonstrate how a web page can fetch information from a database using AJAX technology.

Select a Name in the Box Below Select a Customer: Customer info will be listed here. AJAX Example Explained The example above contains a simple HTML form and a link to a JavaScript: <html> <head> <script src="selectcustomer.js"></script> </head> <body> <form> Select a Customer: <select name="customers" onchange="showCustomer(this.value)"> <option value="ALFKI">Alfreds Futterkiste <option value="NORTS ">North/South <option value="WOLZA">Wolski Zajazd </select> </form> <p> <div id="txtHint"><b>Customer info will be listed here.</b></div> </p> </body> </html> As you can see it is just a simple HTML form with a drop down box called "customers". The paragraph below the form contains a div called "txtHint". The div is used as a placeholder for info retrieved from the web server.
Alfreds Futterkiste

When the user selects data, a function called "showCustomer()" is executed. The execution of the function is triggered by the "onchange" event. In other words: Each time the user change the value in the drop down box, the function showCustomer is called. The JavaScript code is listed below.

The AJAX JavaScript This is the JavaScript code stored in the file "selectcustomer.js": var xmlHttp function showCustomer(str) { xmlHttp=GetXmlHttpObject(); if (xmlHttp==null) { alert ("Your browser does not support AJAX!"); return; } var url="getcustomer.asp"; url=url+"?q="+str; url=url+"&sid="+Math.random(); xmlHttp.onreadystatechange=stateChanged; xmlHttp.open("GET",url,true); xmlHttp.send(null); } function stateChanged() { if (xmlHttp.readyState==4) { document.getElementById("txtHint").innerHTML=xmlHttp.responseText; } } function GetXmlHttpObject() { var xmlHttp=null; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e) { // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } } return xmlHttp; }

The AJAX Server Page The server page called by the JavaScript, is a simple ASP file called "getcustomer.asp". The page is written in VBScript for an Internet Information Server (IIS). It could easily be rewritten in PHP, or some other server language. Look at a corresponding example in PHP. The code runs an SQL against a database and returns the result as an HTML table: <% sql="SELECT * FROM CUSTOMERS WHERE CUSTOMERID=" sql=sql & request.querystring("q") set conn=Server.CreateObject("ADODB.Connection") conn.Provider="Microsoft.Jet.OLEDB.4.0" conn.Open(Server.Mappath("/db/northwind.mdb")) set rs = Server.CreateObject("ADODB.recordset") rs.Open sql, conn response.write("<table>") do until rs.EOF for each x in rs.Fields response.write("<tr><td><b>" & x.name & "</b></td>") response.write("<td>" & x.value & "</td></tr>") next rs.MoveNext loop response.write("</table>") %> AJAX XML Example In the AJAX example below we will demonstrate how a web page can fetch information from an XML file using AJAX technology.

Select a CD in the Box Below Select a CD: CD info will be listed here. AJAX Example Explained The example above contains a simple HTML form and a link to a JavaScript: <html> <head> <script src="selectcd.js"></script> </head> <body> <form> Select a CD: <select name="cds" onchange="showCD(this.value)"> <option value="Bob Dylan">Bob Dylan</option> <option value="Bonnie Tyler">Bonnie Tyler</option> <option value="Dolly Parton">Dolly Parton</option> </select>
Bob Dylan

</form> <p> <div id="txtHint"><b>CD info will be listed here.</b></div> </p> </body> </html> As you can see it is just a simple HTML form with a simple drop down box called "cds". The paragraph below the form contains a div called "txtHint". The div is used as a placeholder for info retrieved from the web server. When the user selects data, a function called "showCD" is executed. The execution of the function is triggered by the "onchange" event. In other words: Each time the user change the value in the drop down box, the function showCD is called. The JavaScript code is listed below.

The AJAX JavaScript This is the JavaScript code stored in the file "selectcd.js": var xmlHttp function showCD(str) { xmlHttp=GetXmlHttpObject(); if (xmlHttp==null) { alert ("Your browser does not support AJAX!"); return; } var url="getcd.asp"; url=url+"?q="+str; url=url+"&sid="+Math.random(); xmlHttp.onreadystatechange=stateChanged; xmlHttp.open("GET",url,true); xmlHttp.send(null); } function stateChanged() { if (xmlHttp.readyState==4) { document.getElementById("txtHint").innerHTML=xmlHttp.responseText; } } function GetXmlHttpObject() { var xmlHttp=null; try { // Firefox, Opera 8.0+, Safari xmlHttp=new XMLHttpRequest(); } catch (e) { // Internet Explorer try { xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");

} catch (e) { xmlHttp=new ActiveXObject("Microsoft.XMLHTTP"); } } return xmlHttp; }

The AJAX Server Page The server page called by the JavaScript, is a simple ASP file called "getcd.asp". The page is written in VBScript for an Internet Information Server (IIS). It could easily be rewritten in PHP, or some other server language. Look at a corresponding example in PHP. The code runs a query against an XML file and returns the result as HTML: <% q=request.querystring("q") set xmlDoc=Server.CreateObject("Microsoft.XMLDOM") xmlDoc.async="false" xmlDoc.load(Server.MapPath("cd_catalog.xml")) set nodes=xmlDoc.selectNodes("CATALOG/CD[ARTIST='" & q & "']") for each x in nodes for each y in x.childnodes response.write("<b>" & y.nodename & ":</b> ") response.write(y.text) response.write("<br />") next next %>

How does AJAX work

The pursuit of a development technique like AJAX came from the need for making web applications much more usable and eliminating their key disadvantages in comparison with the desktop platform:



Poor Interactivity – web applications require that users wait for full page reloads after each interaction with the server. During the loading time they have to stare at a blank screen, which tremendously disturbs the whole experience. Although broadband internet connections are becoming a standard, web applications are also becoming increasingly complex and "heavy" so the overall waiting time



remains relatively the same. Unresponsiveness – classic web applications transfer the complete form data to the server, which in turn renders and sends back the full HTML markup of the page to the browser. This happens during each postback and in most cases is highly

inefficient, since only a small part of the interface is actually changed. However, lots of bandwidth is consumed and the performance is significantly hindered. This leaves users with the idea that web applications are slow by nature. Even worse, the user will often find the page has scrolled to a different position, causing disorientation.



Simplistic Interfaces – the requirement for full page postback whenever the user interface has to be changed imposes hefty limitations on the degree of sophistication of web user interfaces. Rich and smooth interfaces with on-demand update could only be implemented using Flash technology. This approach, however, is impractical for general use since it is very complex and requires a much different set of skills than those possessed by the typical web developer. It



can also cause end-user issues as a plug-in is often required. Low Usability – if a web application reloads the whole page because the user made a new selection on a form, they will get confused. It is often the case that web applications work in a confusing and esoteric way because the web application has been built around the standard, simple view of the Internet protocols. ASP.NET meant we could build applications with more functionality more quickly, usability has a way to go yet.

AJAX was born with the idea to change all this and narrow the functional gap between the desktop and the web. The new generation of AJAX-enabled applications delivers close-toinstantaneous performance, rich interfaces and tremendously improved user experience. It opens new horizons for much closer interaction with the application and demonstrates in practice what was until recently considered impossible:

   

Real-time map panning in Google Maps and Virtual Earth is just like image panning in Adobe® Photoshop® Folder browsing, message previewing, etc. in Microsoft® Outlook® Web Access is identical to that in the desktop version of Outlook. Validation checking on complex input fields can be performed by the server, without reloading the page. Virtual scrolling of huge tables with telerik r.a.d.grid is as fast as in Microsoft Excel®

What's interesting to know is that AJAX is not actually that new as a technology. It has been first used after Microsoft implemented Microsoft.XMLHTTP COM object that was part of The Microsoft® XML Parser distributive. As an ActiveX object in Internet Explorer 5, it was used to create the famous Outlook Web Access. You have probably seen AJAX in action for quite long in the MSDN Documentation treeview navigation. What is new actually is the name AJAX, which was widely accepted in 2005. Other labels for the same technology are Load on Demand, Asynchronous Requests, Callbacks, Out-of-band Calls, etc. What's even more interesting is that AJAX is actually not a technology. It is more like a development technique that utilizes in a unique way a number of already mature technologies: HTML/XHTML, XML, DHTML, the XmlHttpRequest object, and JavaScript. For the purposes of simplicity we will refer to it as technology as it is widely accepted as such and provides a useful language to discuss the characteristics of the significant trend it represents.

How does AJAX work?

The core idea behind AJAX is to make the communication with the server asynchronous, so that data is transferred and processed in the background. As a result the user can continue working on the other parts of the page without interruption. In an AJAX-enabled application only the relevant page elements are updated, only when this is necessary.

In contrast, the traditional synchronous (postback-based) communication would require a full page reload every time data has to be transferred to/from the server. This leads to the following negative effects:

   

The user interaction with the application is interrupted every time a server call is needed, since a postback has to be made. The user has to wait and look at blank screen during each postback. The full page is being rendered and transferred to the client after each postback, which is time consuming and traffic intensive. Any information entered by the user will be submitted to the server, perhaps prematurely.

The AJAX-enabled applications, on the other hand, rely on a new asynchronous method of communication between the client and the server. It is implemented as a JavaScript engine that is loaded on the client during the initial page load. From there on, this engine serves as a mediator that sends only relevant data to the server as XML and subsequently processes server response to update the relevant page elements.

Below is a diagram of the complete lifecycle of an AJAX-enabled web form.

1. Initial request by the browser – the user requests the particular URL.

2. The complete page is rendered by the server (along with the JavaScript AJAX engine) and sent to the client (HTML, CSS, JavaScript AJAX engine). 3. All subsequent requests to the server are initiated as function calls to the JavaScript engine. 4. The JavaScript engine then makes an XmlHttpRequest to the server. 5. The server processes the request and sends a response in XML format to the client (XML document). It contains the data only of the page elements that need to be changed. In most cases this data comprises just a fraction of the total page markup. 6. The AJAX engine processes the server response, updates the relevant page content or performs another operation with the new data received from the server. (HTML + CSS) Example: The AJAX-based VirtualScrolling feature of telerik r.a.d.grid loads on demand only the visible page of the grid, which makes possible to browse of 100,000+ records almost in real-time. (See live demo)

Problems and Challenges
The benefits of the AJAX development technique may look very attractive, but its practical implementation from scratch is usually a complex task, which only advanced developers can undertake. Among the pitfalls you will face are:



Writing and Maintaining Complex JavaScript – building AJAX-enabled applications requires substantial JavaScript skills, which may turn to be a problem for a large number of .Net developers. Furthermore, the lack of good debugging



tools for client-side script makes the process even more complicated. ViewState Management – ASP.NET web controls properly maintain their ViewState between postbacks. The same, however, does not apply for AJAX

callbacks. As a result, developers need to figure a way for the proper management



of the page ViewState. Breaking the Page Paradigm – AJAX requires a different way of thinking about a web-site, since the concept of a "Page" is no longer valid. In fact, AJAX applications may be considered as closer to the desktop-applications development approach. The fact that a Page no longer holds constant data leads to two important consequences – the Back button and bookmarking will no longer work as expected. Therefore, developers need to implement specific mechanisms for overcoming these two issues.



Accessibility – the AJAX development technique fundamentally violates the requirements for accessibility. Since the page content is being updated dynamically, the changes may not be detected by accessibility tools like screen readers. Furthermore, some accessibility standards prohibit the use of JavaScript



altogether, which practically eliminates the possibility for using AJAX. New UI Interactivity Requires Learning – the UI richness of AJAX-enabled application presents users with new and unexpected functionality. Although this is the main reason for using AJAX in the first place, it may require some learning.


				
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