Ajax (programming)

"AJAX" redirects here. For other uses, seeAjax (disambiguation).

Asynchronous JavaScript and XML

First appeared	March 1999
Filename extensions	.js
File formats	JavaScript
Influenced by
JavaScriptandXML

Ajax(alsoAJAX/ˈeɪdʒæks/;short for "AsynchronousJavaScriptandXML"or"AsynchronousJavaScript transfer (x-fer) ") is a set ofweb developmenttechniques that uses various web technologies on theclient-sideto create asynchronousweb applications.With Ajax, web applications can send and retrieve data from aserverasynchronously (in the background) without interfering with the display and behaviour of the existing page. By decoupling thedata interchangelayer 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 utilizeJSONinstead of XML.

Ajax is not a technology, but rather a programming concept.HTMLandCSScan 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-inXMLHttpRequestobject 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 madebandwidtha limiting factor in performance.

In 1996, theiframetag was introduced byInternet Explorer;like theobjectelement,it can load a part of the web page asynchronously. In 1998, the MicrosoftOutlook Web Accessteam developed the concept behind theXMLHttpRequestscripting object.It appeared as XMLHTTP in the second version of theMSXMLlibrary,which shipped withInternet Explorer 5.0in March 1999.

The functionality of the Windows XMLHTTPActiveXcontrol in IE 5 was later implemented byMozilla Firefox,Safari,Opera,Google Chrome,and other browsers as the XMLHttpRequest JavaScript object.Microsoft adopted the native XMLHttpRequest model as ofInternet Explorer 7.The ActiveX version is still supported in Internet Explorer, but not inMicrosoft Edge.The utility of these backgroundHTTPrequests and asynchronous Web technologies remained fairly obscure until it started appearing in large scale online applications such as Outlook Web Access (2000)andOddpost(2002).

Googlemade a wide deployment of standards-compliant,cross browserAjax withGmail(2004) andGoogle Maps(2005).In October 2004Kayak'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 termAJAXwas publicly used on 18 February 2005 byJesse James Garrettin an article titledAjax: A New Approach to Web Applications,based on techniques used on Google pages.

On 5 April 2006, theWorld Wide Web Consortium(W3C) released the first draft specification for the XMLHttpRequest object in an attempt to create an officialWeb standard. The latest draft of the XMLHttpRequest object was published on 6 October 2016,and the XMLHttpRequest specification is now aliving standard.

Technologies

The conventional model for aWeb Applicationversus an application using Ajax

The termAjaxhas 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(orXHTML) andCSSfor presentation
• TheDocument Object Model(DOM) for dynamic display of and interaction with data
• JSONorXMLfor the interchange of data, andXSLTfor XML manipulation
• TheXMLHttpRequestobject for asynchronous communication
• JavaScriptto 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, includingJQuery,include abstractions to assist in executing Ajax requests.

Examples

JavaScript example

An example of a simple Ajax request using theGETmethod, written inJavaScript.

get-ajax-data.js:

// This is the client-side script.

// Initialize the HTTP request.
letxhr=newXMLHttpRequest();
// define the request
xhr.open('GET','send-ajax-data.php');

// Track the state changes of the request.
xhr.onreadystatechange=function(){
constDONE=4;// readyState 4 means the request is done.
constOK=200;// status 200 is a successful return.
if(xhr.readyState===DONE){
if(xhr.status===OK){
console.log(xhr.responseText);// 'This is the output.'
}else{
console.log('Error: '+xhr.status);// An error occurred during the request.
}
}
};

// Send the request to send-ajax-data.php
xhr.send(null);

send-ajax-data.php:

<?php
// This is the server-side script.

// Set the content type.
header('Content-Type: text/plain');

// Send the data back.
echo"This is the output.";
?>

Fetch example

Fetch is a native JavaScript API.According toGoogle 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

asyncfunctiondoAjax1(){
try{
constres=awaitfetch('send-ajax-data.php');
constdata=awaitres.text();
console.log(data);
}catch(error){
console.log('Error:'+error);
}
}

doAjax1();

Fetch relies on JavaScriptpromises.

Thefetchspecification differs fromAjaxin the following significant ways:

• The Promise returned fromfetch()won't reject on HTTP error statuseven if the response is an HTTP 404 or 500. Instead, as soon as the server responds with headers, the Promise will resolve normally (with theokproperty 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 cookiesunless you set thecredentialsinit option. (Since April 2018. The spec changed the default credentials policy tosame-origin.Firefox changed since 61.0b13.)

Benefits

Ajax offers several benefits that can significantly enhance web application performance and user experience. By reducing server traffic and improving speed, Ajax plays a crucial role in modern web development. One key advantage of Ajax is its capacity to render web applications without requiring data retrieval, resulting in reduced server traffic. This optimization minimizes response times on both the server and client sides, eliminating the need for users to endure loading screens.

Furthermore, Ajax facilitates asynchronous processing by simplifying the utilization of XmlHttpRequest, which enables efficient handling of requests for asynchronous data retrieval. Additionally, the dynamic loading of content enhances the application's performance significantly.

Besides, Ajax enjoys broad support across all major web browsers, including Microsoft Internet Explorer versions 5 and above, Mozilla Firefox versions 1.0 and beyond, Opera versions 7.6 and above, and Apple Safari versions 1.2 and higher.

See also

• ActionScript
• Comet (programming)(also known as Reverse Ajax)
• Google Instant
• HTTP/2
• List of Ajax frameworks
• Node.js
• Remote scripting
• Rich web application
• WebSocket
• HTML5
• Web framework
• JavaScript library

External links

• [1]Ajax: A New Approach to Web applications - Article that coined the Ajax term and Q&A
• Ajax (programming)atCurlie
• Ajax Tutorialwith GET, POST, text and XML examples.