Ajax (short for Asynchronous JavaScript and XML) is a technique that is used for the creation of interactive applications for the Web that parse user queries in real-time. The Ajax framework uses several programming tools to achieve that goal. JavaScript, HTML, XML, CSS, the Document Object Model (DOM), and the XMLHttpRequest are all used to create the asynchronous web application. The Ajax script then allows content on the web page to update instantly the moment a visitor performs an action, unlike an HTTP request, which makes the whole page to load again. Because Ajax script is heavily reliant on XMLHttpRequest, the first applications that used it worked only with Internet Explorer browsers. All modern web browsers have full support for Ajax script. Online apps using Ajax utilize an engine that acts as a medium between the web browser and the remote server which holds the requested data. Instead of loading the conventional web page, the web browser fetches the Ajax script engine, which serves the page to the user. The Ajax script engine keeps running in the background, using JavaScript to talk with the browser. An action by the user on the page sends a JavaScript request to the Ajax script engine, which talks back instantly. If the engine needs more information, it sends a query to the server, in most cases via XML, and in the meantime updates the web page.
AJAX Framework
Before HTML5 was supported by web browsers, dynamic pages created with multiple Ajax framework requests didn’t use the browser’s history engine. As a result for the user, clicking the browser’s “back” button didn’t point the browser to a previous state of the Ajax-enabled site, and went back to the previous full website that was visited. Before Ajax programming was introduced a way to circumvent that was to use invisible iframes to cause changes in the browser’s history. The way the Ajax framework does this is by changing the URL fragment identifier when a page with Ajax script in it is accessed and monitors it for changes. HTML5 changed that by providing an API standard for communicating with the browser’s history engine. Dynamic website updates also make “remembering” and returning to a previous state of the application harder. There are solutions to this problem and many of them also use the URL fragment identifier. The solution provided by HTML5 for this problem also applies here. Depending on what kind is the Ajax programming application, dynamic page refreshing may collide with user input, more so if using an unstable Internet connection. For example, typing in a search field may send a query to the server for search completions, but the user may not expect that the suggestion box will appear, and if the Internet connection isn’t quite fast, the suggestion list may appear too late when the user has engaged in another activity.