AJAX ProgrammingHarness the power and speed of AJAX on your website. Note how the whole page does not reload when finding a zip code below...
Ajax, or AJAX (Asynchronous JavaScript and XML), is a group of interrelated web development techniques used to create interactive web applications or rich Internet applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page. The use of Ajax has led to an increase in interactive animation on web pages.Data is retrieved using the XMLHttpRequest object or through the use of Remote Scripting in browsers that do not support it. Despite the name, the use of JavaScript and XML is not actually required, nor do the requests need to be asynchronous.
While the term Ajax was coined in 2005, alternative techniques for the asynchronous loading of content date back to the mid 1990s. Java applets were introduced in the first version of the Java language in 1995. These allow compiled client-side code to load data asynchronously from the web server after a web page is loaded. In 1996, Internet Explorer introduced the IFrame element to HTML, which also enables this to be achieved. In 1999, Microsoft created the XMLHttpRequest object as an ActiveX control in Internet Explorer 5. This is now supported by Mozilla and Safari as native versions of the object. On April 5, 2006 the World Wide Web Consortium (W3C) released the first draft specification for the object in an attempt to create an official web standard.
The term Ajax has come to represent a broad group of web technologies that can be used to implement a web application that communicates with a server in the background, without interfering with the current state of the page. In the article that coined the term Ajax, Jesse James Garrett explained that it refers specifically to these technologies:
- XHTML and CSS for presentation
- the Document Object Model for dynamic display of and interaction with data
- XML and XSLT for the interchange, manipulation and display of data, respectively
- the XMLHttpRequest object for asynchronous communication
- JavaScript to bring these technologies together
- Since then, however, there have been a number of developments in the technologies used in an Ajax application, and the definition of the term Ajax. In particular, it has been noted that:
JavaScript is not the only client-side scripting language that can be used for implementing an Ajax application. Other languages such as VBScript and EGL Programming Language are also capable of the required functionality. XML is not required for data interchange and therefore XSLT is not required for the manipulation of data. JavaScript Object Notation (JSON) is often used as an alternative format for data interchange, although other formats such as preformatted HTML or plain text can also be used.
In many cases, related pages on a website consist of much content that is common between them. Using traditional methods, that content would have to be reloaded on every request. However, using Ajax, a web application can request only the content that needs to be updated, thus drastically reducing bandwidth usage and load time.
The use of asynchronous requests allows the client's Web browser UI to be more interactive and to respond quickly to inputs, and sections of pages can also be reloaded individually. Users may perceive the application to be faster or more responsive, even if the application has not changed on the server side.
The use of Ajax can reduce connections to the server, since scripts and style sheets only have to be requested once.
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