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"AJAX" redirects here. For other uses, see Ajax.

Ajax (asynchronous JavaScript and XML), or AJAX, is a group of inter-related web development techniques used for creating interactive web applications. JavaScript is a Scripting language most often used for Client-side web development Don't change "Extensible" Web development is a broad term for any activity related to developing a Web site for the World Wide Web or an Intranet. In Software engineering, a web application or webapp is an application that is accessed via Web browser over a network such as the Internet A primary characteristic is the increased responsiveness of web pages achieved by exchanging small amounts of data with the server "behind the scenes" so that entire web pages do not have to be reloaded each time there is a need to fetch data from the server. This is intended to increase the web page's interactivity, speed, functionality and usability.

Ajax is asynchronous, in that extra data is requested from the server and loaded in the background without interfering with the display and behavior of the existing page. Asynchrony, in the general meaning is the state of not being synchronized. JavaScript is the scripting language in which Ajax function calls are usually made. JavaScript is a Scripting language most often used for Client-side web development "Scripting" redirects here For other uses see Script. [1] Data is retrieved using the XMLHttpRequest object that is available to scripting languages run in modern browsers, or, alternatively, through the use of Remote Scripting in browsers that do not support XMLHttpRequest. XMLHttpRequest ( XHR) is an API that can be used by JavaScript and other Web browser Scripting languages to transfer XML In its simplest embodiment an object is an allocated region of storage Remote Scripting is a technology which allows scripts running inside a browser to exchange information with a server In any case, it is not required that the asynchronous content be formatted in XML. Don't change "Extensible"

Ajax is a cross-platform technique usable on many different operating systems, computer architectures, and web browsers as it is based on open standards such as JavaScript and the Document Object Model (DOM). In computing cross-platform (also known as multi-platform) is a term used to refer to Computer software or computing methods and concepts that are implemented An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a An open standard is a Standard that is publicly available and has various rights to use associated with it The Document Object Model ( DOM) is a platform- and language -independent standard Object model for representing HTML or XML and related There are free and open source implementations of suitable frameworks and libraries. Free software or software libre is Software that can be used studied and modified without restriction and which can be copied and redistributed in modified or unmodified Open source software (OSS began as a marketing campaign for Free software. A software framework, in Computer programming, is an abstraction in which common code providing generic functionality can be selectively overridden or specialized by user This is a list of notable Web application frameworks used for creating Web applications

Contents

Constituent technologies

Ajax uses a combination of:

Like DHTML and LAMP, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies. Dynamic HTML, or DHTML, is a collection of technologies used together to create interactive and animated Web sites by using a combination of a static Markup The Acronym LAMP refers to a Solution stack of software usually Free and open source software, used to run dynamic Web sites or servers

History

Techniques for the asynchronous loading of content on an existing Web page date back as far as the src attribute, which could take any external URL and load a page containing JavaScript that manipulated the parent page, resulting in Ajax-like effects. Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it This set of client-side technologies was usually grouped together under the generic term DHTML. Dynamic HTML, or DHTML, is a collection of technologies used together to create interactive and animated Web sites by using a combination of a static Markup

Microsoft's Remote Scripting, introduced in 1998, acted as a more elegant replacement for these techniques, with data being pulled in by a Java applet with which the client side could communicate using JavaScript. Remote Scripting is a technology which allows scripts running inside a browser to exchange information with a server A Java applet is an Applet delivered in the form of Java bytecode. This technique worked on both Internet Explorer 4 and Netscape Navigator 4 and onwards. Windows Internet Explorer (formerly Microsoft Internet Explorer abbreviated MSIE) commonly abbreviated to IE, is a series of graphical Netscape Navigator and Netscape are the names for the proprietary Web browser popular in the 1990s and the Flagship product of the Netscape Microsoft then created the XMLHttpRequest object in Internet Explorer 5 and first took advantage of these techniques using XMLHttpRequest in Outlook Web Access supplied with the Microsoft Exchange Server 2000 release. Outlook Web Access ( OWA) is a Webmail service of Microsoft Exchange Server 5 Microsoft Exchange Server is a Messaging and Collaborative software product developed by Microsoft.

The Web development community, first collaborating for remote scripting to enable consistent results across different browsers, created in 2002 a user-community modification to Microsoft Remote Scripting which was created to replace the Java applet with XMLHttpRequest. [2]

Remote Scripting frameworks such as ARSCIF[3] surfaced in 2003 not long before Microsoft introduced callbacks in ASP.NET. ASPNET is a Web application framework developed and marketed by Microsoft, that Programmers can use to build dynamic Web sites Web applications [4]

In addition, the World Wide Web Consortium (W3C) has several recommendations that also allow for dynamic communication between a server and user agent, though few of them are well supported. These would include:

Rationale

The core reason to use Ajax-style programming is to overcome the page loading requirements of HTML/HTTP-mediated web pages. Ajax creates the necessary initial conditions for the evolution of complex, intuitive, dynamic, data-centric user interfaces in web pages. Indeed, much of the Web's innovation and evolution during the Web 2.0 era has relied upon and benefited immensely from the capabilities of an Ajax platform. Web 20 is a term describing changing trends in the use of World Wide Web technology and Web design that aims to enhance Creativity, secure

Web pages, unlike native applications, are loosely coupled, meaning that the data they display are not tightly bound to data sources and must be first marshaled (set out in proper order) into an HTML page format before they can be presented to a user agent on the client machine. Loose coupling describes a resilient relationship between two or more systems or organizations with some kind of exchange relationship A user agent is the client application used with a particular Network protocol; the phrase is most commonly used in reference to those which access the World For this reason, web pages have to be re-loaded each time a user needs to view different datasets. By using the XMLHttpRequest object to request and return data without a re-load, a programmer bypasses this requirement and makes the loosely coupled web page behave much like a tightly coupled application, but with a more variable lag time for the data to pass through a longer "wire" to the remote web browser.

For example, in a classic desktop application, a programmer has the choice of populating a tree view control with all the data needed when the form initially loads, or with just the top-most level of data—which would load more quickly, especially when the dataset is very large. In graphical computing a desktop environment ( DE) commonly refers to a style of Graphical user interface (GUI that is based on the Desktop metaphor which Application software is a subclass of Computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform A tree view or an outline view is a Graphical user interface element ( widget) that presents a hierarchical view of information In the second case, the application would fetch additional data into the tree control depending on which item the user selects. This functionality is difficult to achieve in a web page without Ajax. To update the tree based on a user's selection would require the entire page to re-load, leading to a very jerky, non-intuitive feel for the web user who is browsing the data in the tree.

As a good practice, AJAX should only be used in those pages where communication is done by POST method. Since POST form is generally used to avoid user bookmarking a page, the use of AJAX here perfectly sync with the purpose.

Advantages

Bandwidth usage

By generating the HTML locally within the browser, and only bringing down JavaScript calls and the actual data, Ajax web pages can appear to load relatively quickly since the payload coming down is much smaller in size, and the rest of the layout does not have to be redrawn on each update. An example of this technique is a large result set where multiple pages of data exist. With Ajax, the HTML of the page (e. g. , a table structure with related <tr> and <td> tags) can be produced locally in the browser, not brought down with the first page of the document. In addition to "load on demand" of contents, some web-based applications load stubs of event handlers and then load the functions on the fly. This technique significantly cuts down the bandwidth consumption for web applications. In addition Ajax works on the client and shares some work of the server, reducing the server load.

Separation of data, format, style, and function

A less specific benefit of the Ajax approach is that it tends to encourage programmers to clearly separate the methods and formats used for the different aspects of information delivery via the web. Although Ajax can appear to be a jumble of languages and techniques, and programmers are free to adopt and adapt whatever works for them, they are generally propelled by the development motive itself to adopt separation among the following:

  1. Raw data or content to be delivered, which is normally embedded in XML and sometimes derived from a server-side database. A Computer Database is a structured collection of records or data that is stored in a computer system
  2. Format or structure of the webpage, which is almost always built in HTML or XHTML and is then reflected and made available to dynamic manipulation in the DOM.
  3. Style elements of the webpage: everything from fonts to picture placement are derived by reference to embedded or referenced CSS.
  4. Functionality of the webpage, which is provided by a combination of:
    1. Javascript on the client browser (Also called DHTML),
    2. Standard HTTP and XMLHttp or client-to-server communication, and
    3. Server-side scripting and/or programs using any suitable language preferred by the programmer to receive the client's specific requests and respond appropriately. JavaScript is a Scripting language most often used for Client-side web development Dynamic HTML, or DHTML, is a collection of technologies used together to create interactive and animated Web sites by using a combination of a static Markup

Disadvantages

Browser integration

The dynamically created page does not register itself with the browser history engine, so triggering the "Back" function of the users' browser might not bring the desired result.

Developers have implemented various solutions to this problem. These solutions can involve using invisible IFrames to invoke changes that populate the history used by a browser's back button. IFrame (from Inline Frame) is an HTML element which makes it possible to embed an HTML document inside another HTML document Google Maps, for example, performs searches in an invisible IFRAME and then pulls results back into an element on the visible web page. Google Maps (for a time named Google Local) is a free Web mapping service application and technology provided by Google that powers many map-based services The World Wide Web Consortium (W3C) did not include an iframe element in its XHTML 1. 1 Recommendation; the Consortium recommends the object element instead.

Dynamic web page updates also make it difficult for a user to bookmark a particular state of the application. Solutions to this problem exist, many of which use the URL fragment identifier (the portion of a URL after the '#')[6] to keep track of, and allow users to return to, the application in a given state. In computer Hypertext, a fragment identifier is a short string of characters that refers to a resource that is subordinate to another primary This is possible because many browsers allow JavaScript to update the fragment identifier of the URL dynamically, so that Ajax applications can maintain it as the user changes the application's state. This solution also improves back-button support. It is not, however, a complete solution.

Response-time

Network latency, the interval between user request and server response, must be considered carefully during Ajax development. Latency is a time delay between the moment something is initiated and the moment one of its effects begins or becomes detectable Without clear feedback to the user,[7] preloading of data and proper handling of the XMLHttpRequest object, users might experience delays in the interface of the web application, something which they might not expect or understand. Additionally, when an entire page is rendered there is a brief moment of re-adjustment for the eye as content changes. The lack of this re-adjustment with smaller portions of the screen changing makes the latency more apparent. The use of visual feedback (such as throbbers) to alert the user of background activity and/or preloading of content and data are often-suggested solutions to these latency issues. A throbber is a Graphic usually found in the top-right corner of the Graphical user interface of a Computer program (especially a Web browser

Search engine optimization

Websites that use Ajax to load data which should be indexed by search engines must be careful to provide equivalent data for clients without JavaScript, as search engines do not generally execute the JavaScript code required for Ajax functionality. This problem is not specific to Ajax, as the same issue occurs with sites that provide dynamic data as a full-page refresh in response to, say, a form submit. (The general problem is sometimes called the deep web. The deep Web (also called Deepnet, the invisible Web, or the hidden Web) refers to World Wide Web content that is not part of the Surface )

Reliance on JavaScript and the DOM

Ajax relies on JavaScript and the browser's Document Object Model (DOM), which is often implemented differently by different browsers or versions of a particular browser. The Document Object Model ( DOM) is a platform- and language -independent standard Object model for representing HTML or XML and related Because of this, sites that use JavaScript may need to be tested in multiple browsers to check for compatibility issues. In computing cross-platform (also known as multi-platform) is a term used to refer to Computer software or computing methods and concepts that are implemented It's common to see JavaScript code written twice—one part for Internet Explorer, another part for Mozilla compatibles—although this is less true with the release of IE7 and with the now-common use of JavaScript libraries such as Prototype or jQuery, which abstract browser-specific differences from the web developer. The Prototype JavaScript Framework is a JavaScript framework created by Sam Stephenson which provides an Ajax framework and other utilities jQuery is a lightweight JavaScript library that emphasizes interaction between JavaScript and HTML.

The level of IDE support for JavaScript used to be poor, although it is changing with more wide-spread use of tools like Drosera, Firebug, Microsoft Script Debugger/Editor, Venkman and Dragonfly. In Computing, an integrated development environment ( IDE) is a Software application that provides comprehensive facilities to Computer programmers WebKit is an Open source Application framework that provides a foundation upon which to build a Web browser. The Firebug extension for Mozilla Firefox allows the debugging editing and monitoring of any website's CSS HTML DOM and JavaScript and provides other web development tools Venkman is the JavaScript Debugger component of the Mozilla Application Suite.

Finally, if the user has switched off JavaScript support, pages designed to use Ajax may not function.

Web analytics

Many web analytics solutions expect a new page to be loaded whenever new or updated content is displayed to the user, and after each step in a process such as a check-out. Web analytics is the study of online behaviour in order to improve it Since Ajax alters this process, developers must take care to instrument a page or a portion thereof so that it can be accurately tracked. Analytics systems which can track events other than simple page views, such as clicks of buttons or links, are most able to accommodate Ajax-using sites.

Accessibility

Main article: WAI-ARIA

Non-Ajax users would ideally continue to load and manipulate the whole page as a fall back, enabling the developers to preserve the experience of users in non-Ajax environments (including all relevant accessibility concerns) while giving those with capable browsers a much more responsive experience. WAI-ARIA (Web Accessibility Initiative - Accessible Rich Internet Applications is a draft technical specification expected to become a W3C Recommended Web Standard For this reason it is advised to first develop a full application without Ajax, and implement Ajax enhancements as an addition only (see: Progressive enhancement methodology). Progressive enhancement is a strategy for Web design that emphasizes accessibility semantic markup and external stylesheet and scripting technologies The same counts for JavaScript in general, which can be disabled in most browsers.

Because many people consider it unreasonable to advise against the use of JavaScript in modern web applications, the W3C Web Accessibility Initiative (WAI) is working on a specification for Accessible Rich Internet Applications (ARIA). WAI-ARIA (Web Accessibility Initiative - Accessible Rich Internet Applications is a draft technical specification expected to become a W3C Recommended Web Standard In effect, ARIA allows web pages, or portions of web pages, to declare themselves as applications rather than as documents. This allows Ajax interactions and other types of JavaScript-enabled UI controls to interact with assistive technology, like screen readers for the vision-impaired.

One early user agent implementation is Firefox 3, which maps WAI-ARIA to the accessibility API of the underlying operating system, making it possible for screen readers to treat ARIA widgets in much the same way as the widgets found in client-side software. A user agent is the client application used with a particular Network protocol; the phrase is most commonly used in reference to those which access the World Another early implementation is Fire Vox, an extension that turns Firefox into a self-voicing browser. Fire Vox is a free and Open source extension for the Mozilla Firefox web browser that transforms it into a Self-voicing application Since Fire Vox operates directly on the DOM and does not use the operating system's accessibility API, it can handle WAI-ARIA features, such as live regions, which have no mapping to traditional desktop applications. The Document Object Model ( DOM) is a platform- and language -independent standard Object model for representing HTML or XML and related

Ajax libraries and toolkits are also adopting ARIA. Notable examples include Google Web Toolkit, Backbase and Dojo Toolkit. Google Web Toolkit ( GWT) is an Open source Java software development framework that allows Web developers to create Ajax applications Backbase is a Computer software company specialized in creating Ajax -based Rich Internet applications It was founded in 2003 in Amsterdam The Dojo Toolkit is a modular Open source JavaScript toolkit (or library) designed to ease the rapid development of cross platform JavaScript/ In addition, AxsJAX, a JavaScript library which focuses on web-application accessibility, includes several abstractions built on top of ARIA. AxsJAX (Access-Enabling AJAX is an open source JavaScript library for enhancing the accessibility of Web 2

Patents

Since the beginning of 2006, there have been 2 patents claiming Ajax domains. A patent is a set of Exclusive rights granted by a State to an inventor or his assignee for a fixed period of time in exchange for a disclosure of an

The first, US patent No. 7,000,180, filed in 2001, was issued on Feb 14, 2006. In brief, is entitled methods, systems, and processes for the design and creation of Rich-Media applications via the Internet. It contains 83 claims that encompass a wide range of rich-media net application methods, systems, and processes.

The other, US patent No. 6,418,462, filed in 1999, was issued on July 9, 2002. It is said to "disclose methods allowing clients to perform tasks through a sideband communication channel, in addition to the main communication channel between a client and server".

The validity, effectiveness and enforceability of the claimed patents are unverified.

See also

Notes and references

  1. ^ Because of the varying uses of JavaScript and related variant languages, Javascript is commonly identified as both a programming language and a scripting language. An Ajax framework is a framework that helps to develop web applications that use ''Ajax'', a collection of technologies used to build dynamic web pages on the client Gears, formerly Google Gears, is software offered by Google that "enables more powerful web applications by adding new features to your web browser Progressive enhancement is a strategy for Web design that emphasizes accessibility semantic markup and external stylesheet and scripting technologies Reverse Ajax refers to an Ajax Design pattern that uses long-lived HTTP connections to enable low-latency communication between a Web server Rich Internet applications (RIAs are Web applications that have the features and functionality of traditional desktop applications. XMLHttpRequest ( XHR) is an API that can be used by JavaScript and other Web browser Scripting languages to transfer XML A programming language is an Artificial language that can be used to write programs which control the behavior of a machine particularly a Computer. "Scripting" redirects here For other uses see Script.
  2. ^ HTTPRequest-enabled RS. microsoft. public. scripting. remote newsgroup (2002-06-18). See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. Events 618 - Coronation of the Chinese governor Li Yuan as Emperor Gaozu of Tang, the new Emperor of China, initiating three centuries Retrieved on 2006-08-01. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 30 BC - Octavian (later known as Augustus enters Alexandria, Egypt, bringing it under the control of the Roman
  3. ^ ARSCIF: A Framework for Asynchronous Remote–Script Callback Invocation. Sebastiano Vigna. Retrieved on 2006-08-01. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 30 BC - Octavian (later known as Augustus enters Alexandria, Egypt, bringing it under the control of the Roman
  4. ^ Cutting Edge: Script Callbacks in ASP.NET. MSDN Magazine sujatha reddy ambati (2004-08-08). The Microsoft Developer Network ( MSDN) is the portion of Microsoft responsible for managing the firm's relationship with developers hardware developers interested "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Events 1220 - Sweden is defeated by Estonian tribes in the Battle of Lihula. Retrieved on 2006-08-01. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 30 BC - Octavian (later known as Augustus enters Alexandria, Egypt, bringing it under the control of the Roman
  5. ^ DOM Level 3 Load and Save Specification
  6. ^ Uniform Resource Identifier (URI): Generic Syntax. The Internet Society (January 2005). Retrieved on 2006-07-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 356 BC - Herostratus sets fire to the Temple of Artemis in Ephesus, one of the Seven Wonders of the World
  7. ^ Remote Scripting with Ajax, Part 2. O'Reilly XML. com (2005-08-22). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 392 - Arbogast has Eugenius elected Western Roman Emperor. Retrieved on 2006-07-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 356 BC - Herostratus sets fire to the Temple of Artemis in Ephesus, one of the Seven Wonders of the World

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