Asynchronous JavaScript and JSON
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Ajax (also AJAX ; short for "
Asynchronous Asynchrony is the state of not being in synchronization. Asynchrony or asynchronous may refer to: Electronics and computing * Asynchrony (computer programming), the occurrence of events independent of the main program flow, and ways to deal with ...
JavaScript and XML") is a set of
web development Web development is the work involved in developing a website for the Internet (World Wide Web) or an intranet (a private network). Web development can range from developing a simple single static page of plain text to complex web applications ...
techniques that uses various web technologies on the client-side to create asynchronous web applications. With Ajax, web applications can send and retrieve data from a
server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...
asynchronously (in the background) without interfering with the display and behaviour of the existing page. By decoupling the data interchange layer from the presentation layer, Ajax allows web pages and, by extension, web applications, to change content dynamically without the need to reload the entire page. In practice, modern implementations commonly utilize
JSON JSON (JavaScript Object Notation, pronounced ; also ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and arrays (or other ser ...
instead of XML. Ajax is not a technology, but rather a programming concept. HTML and
CSS Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
can be used in combination to mark up and style information. The webpage can be modified by JavaScript to dynamically display—and allow the user to interact with the new information. The built-in
XMLHttpRequest XMLHttpRequest (XHR) is an API in the form of an object whose methods transfer data between a web browser and a web server. The object is provided by the browser's JavaScript environment. Particularly, retrieval of data from XHR for the purpose o ...
object is used to execute Ajax on webpages, allowing websites to load content onto the screen without refreshing the page. Ajax is not a new technology, nor is it a new language. Instead, it is existing technologies used in a new way.


History

In the early-to-mid 1990s, most Websites were based on complete HTML pages. Each user action required a complete new page to be loaded from the server. This process was inefficient, as reflected by the user experience: all page content disappeared, then the new page appeared. Each time the browser reloaded a page because of a partial change, all the content had to be re-sent, even though only some of the information had changed. This placed additional load on the server and made bandwidth a limiting factor in performance. In 1996, the iframe tag was introduced by Internet Explorer; like the
object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ai ...
element, it can load or fetch content asynchronously. In 1998, the Microsoft
Outlook Web Access Outlook on the web (previously known as Exchange Web Connect, Outlook Web Access, and Outlook Web App) is a personal information manager web app from Microsoft. It includes a web-based email client, a calendar tool, a contact manager, and a ta ...
team developed the concept behind the
XMLHttpRequest XMLHttpRequest (XHR) is an API in the form of an object whose methods transfer data between a web browser and a web server. The object is provided by the browser's JavaScript environment. Particularly, retrieval of data from XHR for the purpose o ...
scripting object. It appeared as XMLHTTP in the second version of the
MSXML Microsoft XML Core Services (MSXML) are set of services that allow applications written in JScript, VBScript, and Microsoft development tools to build Windows-native XML-based applications. It supports XML 1.0, DOM, SAX, an XSLT 1.0 processor, ...
library, which shipped with
Internet Explorer 5.0 Microsoft Internet Explorer 5 (IE5) is a graphical web browser, the fifth version of Internet Explorer, the successor to Internet Explorer 4 and one of the main participants of the first browser war. Its distribution methods and Windows integrat ...
in March 1999. The functionality of the Windows XMLHTTP ActiveX control in IE 5 was later implemented by
Mozilla Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current and a ...
,
Safari A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an importa ...
, Opera,
Google Chrome Google Chrome is a cross-platform web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS ...
, and other browsers as the XMLHttpRequest JavaScript object. Microsoft adopted the native XMLHttpRequest model as of Internet Explorer 7. The ActiveX version is still supported in Internet Explorer, but not in Microsoft Edge. The utility of these background HTTP requests and asynchronous Web technologies remained fairly obscure until it started appearing in large scale online applications such as Outlook Web Access (2000) and Oddpost (2002). Google made a wide deployment of standards-compliant, cross browser Ajax with Gmail (2004) and Google Maps (2005). In October 2004
Kayak.com Kayak (styled as KAYAK) is an American online travel agency and metasearch engine owned and operated by Booking Holdings. Kayak's website and mobile apps are currently available in over 18 languages and more than 30 countries, including the Un ...
's public beta release was among the first large-scale e-commerce uses of what their developers at that time called "the xml http thing". This increased interest in Ajax among web program developers. The term ''AJAX'' was publicly used on 18 February 2005 by
Jesse James Garrett Jesse James Garrett is a User Experience Designer based in San Francisco, California and co-founder of Adaptive Path strategy and design consulting firm. His diagram titled The Elements of User Experience launched his popularity in the web design c ...
in an article titled ''Ajax: A New Approach to Web Applications'', based on techniques used on Google pages. On 5 April 2006, the World Wide Web Consortium (W3C) released the first draft specification for the XMLHttpRequest object in an attempt to create an official Web standard. The latest draft of the XMLHttpRequest object was published on 6 October 2016, and the XMLHttpRequest specification is now a living standard.


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, Jesse James Garrett explained that the following technologies are incorporated: * HTML (or XHTML) and
CSS Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
for presentation * The Document Object Model (DOM) for dynamic display of and interaction with data *
JSON JSON (JavaScript Object Notation, pronounced ; also ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and arrays (or other ser ...
or XML for the interchange of data, and
XSLT XSLT (Extensible Stylesheet Language Transformations) is a language originally designed for transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text or XSL Formatting Objects, which may subseque ...
for XML manipulation * The
XMLHttpRequest XMLHttpRequest (XHR) is an API in the form of an object whose methods transfer data between a web browser and a web server. The object is provided by the browser's JavaScript environment. Particularly, retrieval of data from XHR for the purpose o ...
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 in the definition of the term Ajax itself. XML is no longer required for data interchange and, therefore, XSLT is no longer 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. A variety of popular JavaScript libraries, including JQuery, include abstractions to assist in executing Ajax requests.


Examples


JavaScript example

An example of a simple Ajax request using the
GET Get or GET may refer to: * Get (animal), the offspring of an animal * Get (divorce document), in Jewish religious law * GET (HTTP), a type of HTTP request * "Get" (song), by the Groggers * Georgia Time, used in the Republic of Georgia * Get AS, a ...
method, written in JavaScript. get-ajax-data.js: // This is the client-side script. // Initialize the HTTP request. let xhr = new XMLHttpRequest(); // define the request xhr.open('GET', 'send-ajax-data.php'); // Track the state changes of the request. xhr.onreadystatechange = function () ; // Send the request to send-ajax-data.php xhr.send(null); send-ajax-data.php:


Fetch example

Fetch is a new native JavaScript API. According t
Google Developers Documentation
"Fetch makes it easier to make web requests and handle responses than with the older XMLHttpRequest." fetch('send-ajax-data.php') .then(data => console.log(data)) .catch (error => console.log('Error:' + error));


ES7 async/await example

async function doAjax1() doAjax1(); Fetch relies on JavaScrip
promises
The fetch specification differs from Ajax in the following significant ways: * The Promise returned from fetch() won't reject on HTTP error status even if the response is an HTTP 404 or 500. Instead, as soon as the server responds with headers, the Promise will resolve normally (with the ok property of the response set to false if the response isn't in the range 200–299), and it will only reject on network failure or if anything prevented the request from completing. * fetch() won't send cross-origin cookies unless you set the ''credentials'' init option. (Since April 2018. The spec changed the default credentials policy to same-origin. Firefox changed since 61.0b13.)


See also

* ActionScript * Comet (programming) (also known as Reverse Ajax) * Google Instant * HTTP/2 *
List of Ajax frameworks This is a list of notable Ajax frameworks, used for creating web applications with a dynamic link between the client and the server. Some of the frameworks are JavaScript compilers, for generating JavaScript and Ajax that runs in the web browser cl ...
*
Node.js Node.js is an open-source server environment. Node.js is cross-platform and runs on Windows, Linux, Unix, and macOS. Node.js is a back-end JavaScript runtime environment. Node.js runs on the V8 JavaScript Engine and executes JavaScript code ou ...
*
Remote scripting Remote scripting is a technology which allows scripts and programs that are running inside a browser to exchange information with a server. The local scripts can invoke scripts on the remote side and process the returned information. The earliest ...
*
Rich web application A rich web application (originally called a rich Internet application, or RIA or installable Internet application) is a web application that has many of the characteristics of desktop application software. The concept is closely related to a sing ...
* WebSocket * HTML5 * Web framework * JavaScript library


References


External links



Ajax: A New Approach to Web applications - Article that coined the Ajax term and Q&A *
Ajax Tutorial
with GET, POST, text and XML examples. {{DEFAULTSORT:Ajax (Programming) Ajax (programming), Cloud standards Inter-process communication Web 2.0 neologisms Web development Articles with example JavaScript code Articles with example PHP code