AJAX

Ajax (also AJAX; /ˈeɪdʒæks/; an acronym for Asynchronous JavaScript and XML) is a group of interrelated web development techniques used on the client-side to create asynchronous web applications. With Ajax, web applications can send data to, and retrieve data from, a server asynchronously (in the background) without interfering with the display and behavior of the existing page. Data can be retrieved using the XMLHttpRequest object. Despite the name, the use of XML is not required (JSON is often used instead.

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 updating parts of a web page - without reloading the whole page.

Ajax is not a single technology, but a group of technologies. HTML and CSS can be used in combination to mark up and style information. The DOM is accessed with JavaScript to dynamically display, and allow the user to interact with, the information presented. JavaScript and the XMLHttpRequest object provide a method for exchanging data asynchronously between browser and server to avoid full page reloads.

Head First Ajax gives you an up-to-date perspective that lets you see exactly what you can do -- and has been done -- with Ajax. Using the unique and highly effective visual format that makes Head First titles popular, this book offers a big picture overview to introduce Ajax, and then explores the use of individual Ajax components -- including the JavaScript event model, DOM, XML, JSON, and more -- as it progresses.

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