What is XHR Stands for?
The XHR (XMLHttpRequest) object is the core of the Ajax engine. It is the object that enables a page to get data from (using the GET method) or post data to (using the POST method) the server as a background request, which means that it does not refresh the browser during this process. The XHR eliminates the need to wait on the server to respond with a new page for each request and allows users to continue to interact with the page while the requests are made in the background.
Aside from the background data processing, the GET and POST methods of the XHR object work the same as a standard HTTP request. Using either the POST or the GET method allows you to make a request for data from the server and receive a response in any standardized format. The most common formats in which to receive a response are XML, JSON (JavaScript Object Notation), and text. "The Response." POST is specifically useful when sending data that is larger than 512 bytes (an amount that the GET method cannot handle). After a response is received, the application can be populated with new data from the server by using the DOM with DHTML, which is a combination of XHTML, JavaScript, and CSS.
AJAX Introduction - AJAX, XMLHTTPRequest, XML
Ajax is an acronym for Asynchronous JavaScript and XML, and at its heart is the XMLHTTPRequest object, which is part of the XML DOM (Document Object Model).
The XML (Extensible Markup Language) Document Object Model defines a standard way for accessing and manipulating XML documents. The DOM enables JavaScript to completely access XML or XHTML documents by providing access to the elements which define the structure. The accessibility is possible through a set of intrinsic JavaScript objects that focus on DOM manipulation.It is required to parse the responses that we receive from the server side when we create an XMLHTTPRequest (XHR). As mentioned earlier, the XHR is the core of the Ajax model and without it the model would not exist. This is the piece of the Ajax puzzle that has created the recent buzz because it allows HTTP requests to be made to the server without refreshing the browser.
Ajax is a powerful collection of languages that, when brought together, create extremely intuitive user interfaces and client-side interactions. Although this is true, there are many developers who get so excited by the hype surrounding it that they simply throw the code into their applications without measuring the benefits of using it beforehand. Not every web application has a need for Ajax, but there are many parts of an application that can be enhanced by utilizing its benefits. You will learn usability patterns that will handle feedback, server-side form validation before we even submit the form, and Ajax-enabled components that can enhance sections of our web applications without overdoing it. Ajax is also great to use if you would like to make a server-side connection and possibly a database interaction without refreshing the browser. This is what makes Ajax so powerful because it allows us to interact with the server, receive HTTP status codes, save data to a database, and determine what to present to the user without ever refreshing the page. This request/response pattern can continually persist as a desktop application does, but Ajax-enabled web applications are, well, on the Webaccessible by anyone with a connection, without any downloads or shipping costs for delivering large fancy boxes. The Web is the new desktop, and we are on the verge of a major software shift that we can actively participate in as the pioneers of on-demand information.
Ajax can be a valuable connection between the interface and back-end logic, allowing the back end to be robust and powerful with a simple yet intuitive interface that provides on-demand feedback to users. It also provides ways to exchange data with server-side languages and store it in databases without disconnecting the user from the application like standard applications do when refreshing the browser window.you will have the information needed to create fully functional Ajax applications.
Useful Links on Adobe Flex
