Ajax (programming)

Ajax (also AJAX /ˈeɪdʒæks/; short for asynchronous JavaScript and XML)[1][2] is a set of web development techniques using many web technologies on the client side to create asynchronous web applications. With Ajax, web applications can send and retrieve data from a server asynchronously (in the background) without interfering with the display and behavior 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.[3] In practice, modern implementations commonly utilize JSON instead of XML.

Ajax is not a single technology, but rather a group of technologies. HTML and CSS can be used in combination to mark up and style information. The webpage can then be modified by JavaScript to dynamically display—and allow the user to interact with—the new information. The built-in XMLHttpRequest object within JavaScript is commonly used to execute Ajax on webpages allowing websites to load content onto the screen without refreshing the page. Ajax is not a new technology, or different language, just existing technologies used in new ways.

Asynchronous JavaScript and XML
First appearedMarch 1999
Filename extensions.js
File formatsJavaScript
Influenced by
JavaScript and XML

History

In the early-to-mid 1990s, most Web sites were based on complete HTML pages. Each user action required that a complete new page 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 of 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 on performance.

In 1996, the iframe tag was introduced by Internet Explorer; like the object element, it can load or fetch content asynchronously. In 1998, the Microsoft Outlook Web Access team developed the concept behind the XMLHttpRequest scripting object.[4] It appeared as XMLHTTP in the second version of the MSXML library,[4][5] which shipped with Internet Explorer 5.0 in March 1999.[6]

The functionality of the XMLHTTP ActiveX control in IE 5 was later implemented by Mozilla, Safari, Opera and other browsers as the XMLHttpRequest JavaScript object.[7] 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)[8] and Oddpost (2002).

Google made a wide deployment of standards-compliant, cross browser Ajax with Gmail (2004) and Google Maps (2005).[9] In October 2004 Kayak.com'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".[10] This increased interest in AJAX among web program developers.

The term Ajax was publicly used on 18 February 2005 by Jesse James Garrett in an article titled Ajax: A New Approach to Web Applications, based on techniques used on Google pages.[1]

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.[11] The latest draft of the XMLHttpRequest object was published on 06 October 2016.[12]

Technologies

Ajax-vergleich-en
The conventional model for a Web Application versus an application using Ajax

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][3] Jesse James Garrett explained that the following technologies are incorporated:

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,[13] although other formats such as preformatted HTML or plain text can also be used.[14] A variety of popular JavaScript libraries, including JQuery, include abstractions to assist in executing Ajax requests.

Asynchronous HTML and HTTP (AHAH) involves using XMLHTTPRequest to retrieve (X)HTML fragments, which are then inserted directly into the Web page.

Drawbacks

  • Any user whose browser does not support JavaScript or XMLHttpRequest, or has this functionality disabled, will not be able to properly use pages that depend on Ajax. Simple devices (such as smartphones and PDAs) may not support the required technologies. The only way to let the user carry out functionality is to fall back to non-JavaScript methods. This can be achieved by making sure links and forms can be resolved properly and not relying solely on Ajax.[15]
  • Similarly, some Web applications that use Ajax are built in a way that cannot be read by screen-reading technologies, such as JAWS. The WAI-ARIA standards provide a way to provide hints in such a case.[16]
  • Screen readers that are able to use Ajax may still not be able to properly read the dynamically generated content.[17]
  • The same-origin policy prevents some Ajax techniques from being used across domains,[11] although the W3C has a draft of the XMLHttpRequest object that would enable this functionality.[18] Methods exist to sidestep this security feature by using a special Cross Domain Communications channel embedded as an iframe within a page,[19] or by the use of JSONP.
  • The asynchronous callback-style of programming required can lead to complex code that is hard to maintain, to debug[20] and to test.[21]
  • Because of the asynchronous nature of Ajax, each chunk of data that is sent or received by the client occurs in a connection established specifically for that event. This creates a requirement that for every action, the client must poll the server, instead of listening, which incurs significant overhead. This overhead leads to several times higher latency with Ajax than what can be achieved with a technology such as websockets.[22]
  • In pre-HTML5 browsers, pages dynamically created using successive Ajax requests did not automatically register themselves with the browser's history engine, so clicking the browser's "back" button may not have returned the browser to an earlier state of the Ajax-enabled page, but may have instead returned to the last full page visited before it. Such behavior — navigating between pages instead of navigating between page states — may be desirable, but if fine-grained tracking of page state is required, then a pre-HTML5 workaround was to use invisible iframes to trigger changes in the browser's history. A workaround implemented by Ajax techniques is to change the URL fragment identifier (the part of a URL after the "#") when an Ajax-enabled page is accessed and monitor it for changes.[23][24] HTML5 provides an extensive API standard for working with the browser's history engine.[25]
  • Dynamic Web page updates also make it difficult to bookmark and return to a particular state of the application. Solutions to this problem exist, many of which again use the URL fragment identifier.[23][24] On the other hand, as AJAX-intensive pages tend to function as applications rather than content, bookmarking interim states rarely makes sense. Nevertheless, the solution provided by HTML5 for the above problem also applies for this.[25]
  • Depending on the nature of the Ajax application, dynamic page updates may disrupt user interactions, particularly if the Internet connection is slow or unreliable. For example, editing a search field may trigger a query to the server for search completions, but the user may not know that a search completion popup is forthcoming, and if the Internet connection is slow, the popup list may show up at an inconvenient time, when the user has already proceeded to do something else.
  • Excluding Google,[26] most major Web crawlers do not execute JavaScript code,[27] so in order to be indexed by Web search engines, a Web application must provide an alternative means of accessing the content that would normally be retrieved with Ajax. It has been suggested that a headless browser may be used to index content provided by Ajax-enabled websites, although Google is no longer recommending the Ajax crawling proposal they made in 2009.[28]

Examples

JavaScript example

An example of a simple Ajax request using the GET method, written in JavaScript.

get-ajax-data.js:

// This is the client-side script.

// Initialize the HTTP request.
var xhr = new XMLHttpRequest();
xhr.open('GET', 'send-ajax-data.php');

// Track the state changes of the request.
xhr.onreadystatechange = function () {
	var DONE = 4; // readyState 4 means the request is done.
	var OK = 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.";
?>

Many developers dislike the syntax used in the XMLHttpRequest object, so some of the following workarounds have been created.

jQuery example

The popular JavaScript library jQuery has implemented abstractions which enable developers to use Ajax more conveniently. Although it still uses XMLHttpRequest behind the scenes, the following is the same example as above using the 'ajax' method.

$.ajax({
	type: 'GET',
	url: 'send-ajax-data.php',
	dataType: "JSON", // data type expected from server
	success: function (data) {
		console.log(data);
	},
	error: function() {
		console.log('Error: ' + data);
	}
});

jQuery also implements a 'get' method which allows the same code to be written more concisely.

$.get('send-ajax-data.php').done(function(data) {
	console.log(data);
}).fail(function(data) {
	console.log('Error: ' + data);
});

Fetch example

Fetch is a new native JavaScript API. Although not yet supported by all browsers, it is gaining momentum as a more popular way to execute Ajax. According to 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 doAjax() {
    try {
        const res = await fetch('send-ajax-data.php');
        const data = await res.text();
        console.log(data);
    } catch (error) {
        console.log(error);
    }
}

doAjax();

As seen above, fetch relies on JavaScript promises.

See also

References

  1. ^ a b c Jesse James Garrett (18 February 2005). "Ajax: A New Approach to Web Applications". AdaptivePath.com. Retrieved 19 June 2008.
  2. ^ "Ajax - Web developer guides". MDN Web Docs. Retrieved 27 February 2018.
  3. ^ a b Ullman, Chris (March 2007). Beginning Ajax. wrox. ISBN 978-0-470-10675-4. Archived from the original on 5 July 2008. Retrieved 24 June 2008.
  4. ^ a b "Article on the history of XMLHTTP by an original developer". Alexhopmann.com. 31 January 2007. Archived from the original on 23 June 2007. Retrieved 14 July 2009.
  5. ^ "Specification of the IXMLHTTPRequest interface from the Microsoft Developer Network". Msdn.microsoft.com. Retrieved 14 July 2009.
  6. ^ Dutta, Sunava (23 January 2006). "Native XMLHTTPRequest object". IEBlog. Microsoft. Retrieved 30 November 2006.
  7. ^ "Dynamic HTML and XML: The XMLHttpRequest Object". Apple Inc. Retrieved 25 June 2008.
  8. ^ Hopmann, Alex. "Story of XMLHTTP". Alex Hopmann’s Blog. Archived from the original on 30 March 2010. Retrieved 17 May 2010.
  9. ^ "A Brief History of Ajax". Aaron Swartz. 22 December 2005. Retrieved 4 August 2009.
  10. ^ English, Paul. "Kayak User Interface". OFFICIAL KAYAK.COM TECHNOBLOG. Retrieved 22 May 2014.
  11. ^ a b van Kesteren, Anne; Jackson, Dean (5 April 2006). "The XMLHttpRequest Object". W3.org. World Wide Web Consortium. Archived from the original on 16 May 2008. Retrieved 25 June 2008.
  12. ^ Kesteren, Anne; Aubourg, Julian; Song, Jungkee; Steen, Hallvord R. M. "XMLHttpRequest Level 1". W3.org. W3C. Retrieved 19 February 2019.
  13. ^ "JavaScript Object Notation". Apache.org. Archived from the original on 16 June 2008. Retrieved 4 July 2008.
  14. ^ "Speed Up Your Ajax-based Apps with JSON". DevX.com. Archived from the original on 4 July 2008. Retrieved 4 July 2008.
  15. ^ Quinsey, Peter. "User-proofing Ajax".
  16. ^ "WAI-ARIA Overview". W3C. Archived from the original on 26 October 2010. Retrieved 21 October 2010.
  17. ^ Edwards, James (5 May 2006). "Ajax and Screenreaders: When Can it Work?". sitepoint.com. Retrieved 27 June 2008.
  18. ^ "Access Control for Cross-Site Requests". World Wide Web Consortium. Archived from the original on 14 May 2008. Retrieved 27 June 2008.
  19. ^ "Secure Cross-Domain Communication in the Browser". The Architecture Journal (MSDN). Archived from the original on 29 March 2010. Retrieved 27 April 2010.
  20. ^ Cuthbertson, Tim. "What is asynchronous programming, and why is it so damn awkward?". GFX Monk. Retrieved 19 October 2010.
  21. ^ "Selenium documentation: Fetching a Page". Selenium. Retrieved 6 October 2011.
    It is worth noting that if your page uses a lot of Ajax on load then WebDriver may not know when it has completely loaded. If you need to ensure such pages are fully loaded, then you can use Explicit and Implicit Waits.
  22. ^ Pimentel, Victoria; Nickerson, Bradford G. (8 May 2012). "Communicating and Displaying Real-Time Data with WebSocket". Internet Computing, IEEE. 16 (4): 45–53. doi:10.1109/MIC.2012.64.
  23. ^ a b "Why use Ajax?". InterAKT. 10 November 2005. Archived from the original on 29 May 2008. Retrieved 26 June 2008.
  24. ^ a b "Deep Linking for AJAX".
  25. ^ a b "HTML5 specification". Retrieved 21 October 2011.
  26. ^ Hendriks, Erik (23 May 2014). "Official news on crawling and indexing sites for the Google index". Google. Retrieved 24 May 2015.
  27. ^ Prokoph, Andreas (8 May 2007). "Help Web crawlers efficiently crawl your portal sites and Web sites". IBM. Retrieved 22 April 2009.
  28. ^ "Deprecating our AJAX crawling scheme". Google Webmaster Central Blog. 14 October 2015.

External links

ASP.NET AJAX

ASP.NET AJAX, formerly called Atlas, is a set of extensions to ASP.NET developed by Microsoft for implementing Ajax functionality. It is released under the Microsoft Public License (Ms-PL).

Ace (editor)

Ace (from Ajax.org Cloud9 Editor) is a standalone code editor written in JavaScript. The goal is to create a web-based code editor that matches and extends the features, usability, and performance of existing native editors such as TextMate, Vim, or Eclipse. It can be easily embedded in any web page and JavaScript application. Ace is developed as the primary editor for Cloud9 IDE and as the successor of the Mozilla Skywriter project.MediaWiki also uses Ace

Angular (web framework)

Angular (commonly referred to as "Angular 2+" or "Angular v2 and above") is a TypeScript-based open-source web application framework led by the Angular Team at Google and by a community of individuals and corporations. Angular is a complete rewrite from the same team that built AngularJS.

Apache XAP

XAP (eXtensible Ajax Platform) is a software product presently under development at the Apache Software Foundation. XAP is an XML-based declarative framework for building interactive Ajax web applications. Developers hope to create a product that will interface with various Ajax software toolkits, reduce the need of program scripting and solve the development challenge as well as application maintenance challenges associated with Ajax programming.

XAP applications are defined using the XAL programming language, which differs from available declarative user interface languages in that it also includes declarations pointing to local or http-requestable data sources. XAL also makes provision for algorithmic alteration or replacement of the initially declared interface — for example, a button or link can easily be made to add a new piece of page layout to the page, defined using either XAL or HTML.

Chaplin.js

Chaplin.js is an open-source client-side JavaScript web framework based on the model–view–controller (MVC) software architectural pattern. Chaplin.js uses the Backbone.js library and is intended for developing single-page applications.

Citadel/UX

Citadel/UX (typically referred to simply as "Citadel") is a collaboration suite (messaging and groupware) that is descended from the Citadel family of programs which became popular in the 1980s and 1990s as a bulletin board system platform. It is designed to run on open source operating systems such as Linux or BSD. Although it is being used for many bulletin board systems, in 1998 the developers began to expand its functionality to a general purpose groupware platform.

In order to modernize the Citadel platform for the Internet, the Citadel/UX developers added functionality such as shared calendars, instant messaging, and built-in implementations of Internet protocols such as SMTP, IMAP, Sieve, POP3, GroupDAV and XMPP. All protocols offer OpenSSL encryption for additional security.

Users of Citadel/UX systems also have available to them a web-based user interface which employs Ajax style functionality to allow application-like interaction with the system.

Citadel uses the Berkeley DB database for all of its data stores, including the message base.

Citadel/UX became free and open-source software subject to the terms of the GNU General Public License (GPLv2) in 1999. In 2007 Citadel was relicensed to the GPLv3.

Echo (framework)

Echo is a web application framework created by the company NextApp. The latest iteration, Echo3, allows writing applications in either server-side Java or client-side JavaScript. Server-side applications do not require developer knowledge of HTML, HTTP, or JavaScript. Client-side JavaScript-based applications do not require a server, but can communicate with one via AJAX.

It is free software licensed under the terms of the Mozilla Public License (MPL).

Google APIs

Google APIs is a set of application programming interfaces (APIs) developed by Google which allow communication with Google Services and their integration to other services. Examples of these include Search, Gmail, Translate or Google Maps. Third-party apps can use these APIs to take advantage of or extend the functionality of the existing services.

The APIs provide functionality like analytics, machine learning as a service (the Prediction API) or access to user data (when permission to read the data is given). Another important example is an embedded Google map on a website, which can be achieved using the Static maps API, Places API or Google Earth API.

ICEfaces

ICEfaces is an open-source Software development kit that extends JavaServer Faces (JSF) by employing Ajax. It is used to construct rich Internet applications (RIA) using the Java programming language. With ICEfaces, the coding for interaction and Ajax on the client side is programmed in Java, rather than in JavaScript, or with plug-ins.

JWt (Java web toolkit)

JWt (pronounced "jay-witty") is an open-source widget-centric web application framework for the Java programming language developed by Emweb. It has an API that uses established GUI application development patterns. The programming model is component-based and event-driven, similar to Swing.

The goal of the library is to benefit from the stateful component model used in desktop applications APIs, applied to web development, instead of the traditional model–view–controller (MVC) model. Rather than using MVC at the level of a page, MVC is pushed to the level of individual components.

While the library uses a desktop application development model, it does support web-specific features including semantic URLs, browser history navigation support, internationalization, themes and styling, ...

A unique feature of the library is its abstraction layer of the browser rendering model. The library uses Ajax for communicating with Ajax-capable browsers, while using plain HTML form post-backs for other user agents (for accessibility and search engines). Using a progressive bootstrap method, the user interface is initially rendered as plain HTML, and for Ajax-capable browsers, it is automatically upgraded to use Ajax for increased interactivity. In this way, it is the only server-side framework that implements progressive enhancement automatically, and the only Ajax framework with search engine optimization (SEO) qualities.JWt is distributed as a jar file. A JWt application is a war file that is deployed in a standards-compliant servlet container.

Knockout (web framework)

Knockout is a standalone JavaScript implementation of the Model-View-ViewModel pattern with templates. The underlying principles are therefore:

a clear separation between domain data, view components and data to be displayed

the presence of a clearly defined layer of specialized code to manage the relationships between the view componentsThe latter leverages the native event management features of the JavaScript language.

These features streamline and simplify the specification of complex relationships between view components, which in turn make the display more responsive and the user experience richer.

Knockout was developed and is maintained as an open source project by Steve Sanderson.

Prototype JavaScript Framework

The Prototype JavaScript Framework is a JavaScript framework created by Sam Stephenson in February 2005 as part of the foundation for Ajax support in Ruby on Rails. It is implemented as a single file of JavaScript code, usually named prototype.js. Prototype is distributed standalone, but also as part of larger projects, such as Ruby on Rails, script.aculo.us and Rico. As of November 2015, according to one survey, Prototype is used by 2.2% of all websites.

Qooxdoo

qooxdoo is an open-source Ajax web application framework. It is an LGPL- and/or EPL-licensed client-side and server-agnostic solution, and includes support for professional JavaScript development, a graphical user interface (GUI) toolkit and high-level client-server communication.

Rico (Ajax)

Rico was an open-source JavaScript library for developing rich internet applications with Ajax. Rico builds on the Prototype JavaScript Framework, adding drag-and-drop, animation effects, and other tools.

Script.aculo.us

script.aculo.us is a JavaScript library built on the Prototype JavaScript Framework, providing dynamic visual effects and user interface elements via the Document Object Model (DOM).

It is most notably included with Ruby on Rails and Seaside, but also provided separately to work with other web frameworks and scripting languages.

script.aculo.us was extracted by Thomas Fuchs from his work on fluxiom, a web based digital asset management tool by the design company wollzelle. It was first released to the public in June 2005.

SmartClient

SmartClient is set of mobile and cross-browser HTML5 UI components combined with a Java-based Ajax framework, created by Isomorphic Software to build business web applications. First released in 2001, SmartClient was integrated into products from the software vendors including Informatica, RedHat, IBM, LogicalDOC, EMC and the Copyright Clearance Center.

Since November 2007, SmartClient is available free under an open source LGPL licence, and some of its code may be available on GitHub. It is also available under a commercial licence.SmartClient mentions among its competitors Vaadin, Apache Flex and Sencha's Ext JS, and is similar to full-stack business web application development frameworks like Wakanda.It offers an expansive editable showcase application in order to get to know the software better.

SproutCore

SproutCore is an open-source JavaScript web framework. Its goal is to allow developers to create web applications with advanced capabilities and a user experience comparable to that of desktop applications. When developing a SproutCore application, all code is written in JavaScript. A notable fork of SproutCore is Ember.js. Both projects are maintained separately and have taken different directions.

WAI-ARIA

Web Accessibility Initiative – Accessible Rich Internet Applications (WAI-ARIA) is a technical specification published by the World Wide Web Consortium (W3C) that specifies how to increase the accessibility of web pages, in particular, dynamic content, and user interface components developed with Ajax, HTML, JavaScript, and related technologies.

Wakanda (software)

Wakanda is a JavaScript platform to develop and run web or mobile apps.

It is based on open standards technologies including AngularJS, Ionic, Node.js, and TypeScript, and is supported on Linux (deployment only), Microsoft Windows, and macOS (Studio development).

Server-side
Client-side
Topics
Code analysis
Transcompilers
Concepts
Debuggers
Doc generators
Editors (comparison)
Engines
Frameworks
Related technologies
Package managers
Server-side
Unit testing
People

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.