Ajax (programming)

Last updated

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

Ajax (also AJAX /ˈæks/ ; 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 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. [3] In practice, modern implementations commonly utilize JSON instead of XML.

Contents

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, or since 2017 the new fetch function 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 a different language, just existing technologies used in new ways.

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 Windows 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 6 October 2016, [12] and the XMLHttpRequest specification is now a living standard. [13]

Technologies

The conventional model for a Web Application versus an application using Ajax Ajax-vergleich-en.svg
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, [14] although other formats such as preformatted HTML or plain text can also be used. [15] A variety of popular JavaScript libraries, including JQuery, include abstractions to assist in executing Ajax requests.

Drawbacks

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.varxhr=newXMLHttpRequest();xhr.open('GET','send-ajax-data.php');// Track the state changes of the request.xhr.onreadystatechange=function(){varDONE=4;// readyState 4 means the request is done.varOK=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.phpxhr.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 disliked the syntax used in the XMLHttpRequest object, so some of them applied workarounds that are no longer needed since Fetch.

Fetch example

Fetch is a new native JavaScript API. [28] 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:

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

As seen above, fetch relies on JavaScript promises.


The fetch specification differs from Ajax in the following significant ways:

See also

Related Research Articles

Web application Application that uses a web browser as a client

A web application is application software that runs on a web server, unlike computer-based software programs that are run locally on the operating system (OS) of the device. Web applications are accessed by the user through a web browser with an active network connection. These applications are programmed using a client–server modeled structure—the user ("client") is provided services through an off-site server that is hosted by a third-party. Examples of commonly-used web applications include: web-mail, online retail sales, online banking, and online auctions.

XForms is an XML format used for collecting inputs from web forms. XForms was designed to be the next generation of HTML / XHTML forms, but is generic enough that it can also be used in a standalone manner or with presentation languages other than XHTML to describe a user interface and a set of common data manipulation tasks.

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 of continually modifying a loaded web page is the underlying concept of Ajax design. Despite the name, XHR can be used with protocols other than HTTP and data can be in the form of not only XML, but also JSON, HTML or plain text.

Dynamic web page Type of web page

A server-side dynamic web page is a web page whose construction is controlled by an application server processing server-side scripts. In server-side scripting, parameters determine how the assembly of every new web page proceeds, including the setting up of more client-side processing.

In computing, the same-origin policy is an important concept in the web application security model. Under the policy, a web browser permits scripts contained in a first web page to access data in a second web page, but only if both web pages have the same origin. An origin is defined as a combination of URI scheme, host name, and port number. This policy prevents a malicious script on one page from obtaining access to sensitive data on another web page through that page's Document Object Model.

A web framework (WF) or web application framework (WAF) is a software framework that is designed to support the development of web applications including web services, web resources, and web APIs. Web frameworks provide a standard way to build and deploy web applications on the World Wide Web. Web frameworks aim to automate the overhead associated with common activities performed in web development. For example, many web frameworks provide libraries for database access, templating frameworks, and session management, and they often promote code reuse. Although they often target development of dynamic web sites, they are also applicable to static websites.

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.

Dojo Toolkit

Dojo Toolkit is an open-source modular JavaScript library designed to ease the rapid development of cross-platform, JavaScript/Ajax-based applications and web sites. It was started by Alex Russell, Dylan Schiemann, David Schontzler, and others in 2004 and is dual-licensed under the modified BSD license or the Academic Free License.

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).

Comet is a web application model in which a long-held HTTPS request allows a web server to push data to a browser, without the browser explicitly requesting it. Comet is an umbrella term, encompassing multiple techniques for achieving this interaction. All these methods rely on features included by default in browsers, such as JavaScript, rather than on non-default plugins. The Comet approach differs from the original model of the web, in which a browser requests a complete web page at a time.

YUI Library

The Yahoo! User Interface Library (YUI) is a discontinued open-source JavaScript library for building richly interactive web applications using techniques such as Ajax, DHTML, and DOM scripting. YUI includes several core CSS resources. It is available under a BSD License. Development on YUI began in 2005 and Yahoo! properties such as My Yahoo! and the Yahoo! front page began using YUI in the summer of that year. YUI was released for public use in February 2006. It was actively developed by a core team of Yahoo! engineers.

jQuery is a JavaScript library designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax. It is free, open-source software using the permissive MIT License. As of May 2019, jQuery is used by 73% of the 10 million most popular websites. Web analysis indicates that it is the most widely deployed JavaScript library by a large margin, having at least 3 to 4 times more usage than any other JavaScript library.

JsonML, the JSON Markup Language is a lightweight markup language used to map between XML and JSON. It converts an XML document or fragment into a JSON data structure for ease of use within JavaScript environments such as a web browser, allowing manipulation of XML data without the overhead of an XML parser.

ItsNat Natural AJAX, is an open-source Java component-based Ajax framework.

JSONP, or JSON-P, is a historical JavaScript technique for requesting data by loading a <script> element, which is an element intended to load ordinary JavaScript. It was proposed by Bob Ippolito in 2005. JSONP enables sharing of data bypassing same-origin policy, which disallows running JavaScript code to read media DOM elements or XMLHttpRequest data fetched from outside the page's originating site. The originating site is indicated by a combination of URI scheme, host name, and port number.

A single-page application (SPA) is a web application or website that interacts with the user by dynamically rewriting the current web page with new data from the web server, instead of the default method of a web browser loading entire new pages. The goal is faster transitions that make the website feel more like a native app.

ZK is an open-source Ajax Web application framework, written in Java, that enables creation of graphical user interfaces for Web applications with little required programming knowledge.

Cross-origin resource sharing (CORS) is a mechanism that allows restricted resources on a web page to be requested from another domain outside the domain from which the first resource was served.

Cross-site request forgery, also known as one-click attack or session riding and abbreviated as CSRF or XSRF, is a type of malicious exploit of a website where unauthorized commands are submitted from a user that the web application trusts. There are many ways in which a malicious website can transmit such commands; specially-crafted image tags, hidden forms, and JavaScript XMLHttpRequests, for example, can all work without the user's interaction or even knowledge. Unlike cross-site scripting (XSS), which exploits the trust a user has for a particular site, CSRF exploits the trust that a site has in a user's browser.

References

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