AJAX is asynchronous JavaScript and XML. It is used in creating better, faster, and more interactive web systems or applications. Asynchronous data is transferred between browser and server using the AJAX application. AJAX sends and retrieves data without the need to reload the webpage. 

•    GMAIL
•    Twitter
•    Facebook
•    Javapoint
•    Youtube

AJAX applications include both browser based and platform independent applications.

The unique features of AJAX are as follows:
•    Client-side template rendering
•    Data binding in live environment
•    Declarative initiation of client components
•    Observer pattern on JavaScript objects and arrays
•    Invoking ADO.NET data services and data contexts
•    DataView Control

PROS:
•    It allows for maximum bandwidth utilization
•    Data transfer is more efficient and faster
•    Only important data is transferred to the server
•    User is not blocked till the data is retrieved from the server
CONS:
•    AJAX applications are not fully secure
•    They rely on JavaScript
•    Debugging of AJAX applications is difficult

Synchronous request: In a synchronous request the client blocks and waits for the result of the remote request before continuing execution.
Asynchronous request: Here the client continues execution after initiating the request and processes the result whenever it is made available by the AppServer. It is an important mechanism in responding to the user without any delay where a user can continue execution of code without waiting for the response from the server for the previous requests.
 

The two types of triggers available in the update panel are 
PostBack Trigger: It is a full postback trigger and it cannot work asynchronously.
AsyncPostBack Trigger: It is a partial post back trigger that works asynchronously.

Yes. Java Enterprise Edition servers are used to generate AJAX consumer pages and to manipulate server aspect nations for AJAX customers. It is also used for generating AJAX consumer pages and to serve incoming AJAX requests. The JavaServer Faces aspect version is an exceptional tool for defining and implementing AJAX components.

The primary functionality of XMLHttpRequest include:
•    Sending data in the background to the server
•    Requesting data from the server
•    Receiving data from the server 
•    Updating data without reloading the page
9.    What are the controls available in AJAX?
The various controls available in AJAX are:
•    Timer
•    ScriptManager
•    ScriptManagerProxy
•    UpdatePanel
•    Update Progress 

The DLL containing AJAX control tool kit is Ajaxcontroltoolkit.dll that can be downloaded from the internet and added in the toolbox or copied into the bin folder.

There are two methods used in AJAX for cross domain AJAX calls used to transfer data between two or more security domains. These are:
CORS: Cross Origin Resource Sharing that works with the HTTP web browsers
JSON: It is a padding that works with the HTTP GET and on legacy browsers

JSON is used to exchange data between a browser and a server. It stands for JavaScript Object Notation. Data exchange through JSON is faster than XML and it is easy to understand. Array, object, string, number, and values are supported by JSON.

AJAX applications debugging tools include:
•    JavaScript HTML debugger
•    Firebug for Mozilla Firefox
•    Fiddler for IE (Internet Explorer)
•    My Eclipse AJAX tools
•    Script Debugger

AJAX application consists of 5 different ready states.
•    UNOPENED
•    OPENED
•    HEADERS_RECEIVED
•    LOADING
•    DONE

AJAX    JavaScript
AJAX sends requests to the server and performs other operations on the page without waiting for the response from the server    JavaScript waits for the response from the server after sending a request
AJAX downloads the page without the need for refreshing the page    JavaScript manages a webpage after downloading it.
The overload on the server is reduced by AJAX applications as the request for script is done only once     In JavaScript the request is posted every time the script is posted

AJAX is a built-in functionality of .NET framework 4.0. Installation of Microsoft Visual studio is necessary to execute AJAX applications.
It is necessary to install AJAX Control Toolkit for using AJAX extenders. After installation copy the AJAXControlToolkit.dll file to the Bin directory of your application.

It is a free framework used to implement AJAX in asp.net web applications. It is used to quickly create efficient and interactive web applications that are compatible on all browsers.

AJAX applications consist of the ReadyState property for determining if the AJAX request is completed. If the value of the property is four then it means the request is completed.

AJAX applications are not compatible on all browsers. The following are the list of browsers AJAX is compatible with:
•    IE 5.0 and above
•    Safari 1.2 and above
•    Netscape 7.1 and above
•    Opera 7.7 and above  

Script Manager is used to manage the client side script of AJAX applications. All AJAX applications depend on JavaScript and hence Script Manager acts as a mediator. Every AJAX page has a Script Manager to enable libraries.

•    XMLHttpRequest is used to place a request with the web server
•    HTTP’s GET or POST
•    Uses JSON to communicate between the client and server
•    UED or URL encoded data