Essentials of Javascript - Cultural View

Ajax (programming) 48
Ajax (programming)
Ajax (pronounced English pronunciation: /ˈeɪˌdʒæks/) (shorthand for Asynchronous JavaScript and XML [1] ) is a group
of interrelated web development techniques used on the client-side to create interactive web 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 techniques has led to an increase in interactive or dynamic
interfaces on web pages. Data is usually retrieved using the XMLHttpRequest object. Despite the name, the use of
XML is not actually required, nor do the requests need to be asynchronous. [2]
Like DHTML and LAMP, Ajax is not a technology in itself, but a group of technologies. Ajax uses a combination of
HTML and CSS to mark up and style information. The DOM is accessed with JavaScript to dynamically display,
and to 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.
History
In the 1990s, most web sites were based on complete HTML pages; each user action required that the page be
re-loaded from the server (or a new page loaded). This process is not efficient, as reflected by the user experience (all
page content disappears then reappears, etc.). Each time a page is reloaded due to a partial change, all of the content
must be re-sent instead of just the changed information. This can place additional load on the server and use
excessive bandwidth.
Asynchronous loading of content first became practical when 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. [3] In 1996, Internet Explorer introduced the IFrame element to HTML, which also enabled
asynchronous loading. [4] In 1999, Microsoft created the XMLHTTP ActiveX control in Internet Explorer 5, which
[4] [5]
was later adopted by Mozilla, Safari, Opera and other browsers as the native XMLHttpRequest object.
Microsoft has adopted the native XMLHttpRequest model as of Internet Explorer 7, though the ActiveX version is
still supported. The utility of background HTTP requests to the server and asynchronous web technologies remained
fairly obscure until it started appearing in full scale online applications such as Outlook Web Access,(2000) [6]
Oddpost (2002), and later, notably Google made a wide deployment of Ajax with Gmail (2004) and Google Maps
(2005). [7]
The term "Ajax" was coined in 2005 by Jesse James Garrett. [1] However, a patent application covering this type of
user interface was filed on September 3, 2003, thus predating the term itself by two years. This application resulted
in US Patent #7,523,401 being issued to Greg Aldridge of Kokomo, IN. [8]
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. [7]
Technologies
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, [1] Jesse James Garrett explained that the following technologies are required:
• HTML or XHTML and CSS for presentation
• the Document Object Model for dynamic display of and interaction with data
• XML for the interchange of data, and XSLT for its manipulation
• the XMLHttpRequest object for asynchronous communication
• JavaScript to bring these technologies together