JavaScript

JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles. JavaScript was formalized in the ECMAScript language standard and is primarily used in the form of client-side JavaScript, implemented as part of a Web browser in order to provide enhanced user interfaces and dynamic websites. This enables programmatic access to computational objects within a host environment.

JavaScript's use in applications outside Web pages — for example in PDF documents, site-specific browsers, and desktop widgets — is also significant. Newer and faster JavaScript VMs and frameworks built upon them (notably Node.js) have also increased the popularity of JavaScript for server-side web applications.

JavaScript uses syntax influenced by that of C. JavaScript copies many names and naming conventions from Java, but the two languages are otherwise unrelated and have very different semantics. The key design principles within JavaScript are taken from the Self and Scheme programming languages.

"JavaScript" is a trademark of Oracle Corporation . It is used under license for technology invented and implemented by Netscape Communications and current entities such as the Mozilla Foundation.

The primary use of JavaScript is to write functions that are embedded in or included from HTML pages and that interact with the Document Object Model (DOM) of the page. Some simple examples of this usage are: Opening or popping up a new window with programmatic control over the size, position, and attributes of the new window (e.g. whether the menus, toolbars, etc., are visible).

Validating input values of a web form to make sure that they are acceptable before being submitted to the server. Changing images as the mouse cursor moves over them: This effect is often used to draw the user's attention to important links displayed as graphical elements.

Because JavaScript code can run locally in a user's browser (rather than on a remote server), the browser can respond to user actions quickly, making an application more responsive. Furthermore, JavaScript code can detect user actions which HTML alone cannot, such as individual keystrokes. Applications such as Gmail take advantage of this: much of the user-interface logic is written in JavaScript, and JavaScript dispatches requests for information (such as the content of an e-mail message) to the server. The wider trend of Ajax programming similarly exploits this strength.

• JavaScript engine (also known as JavaScript interpreter or JavaScript implementation) is an interpreter that interprets JavaScript source code and executes the script accordingly. The first JavaScript engine was created by Brendan Eich at Netscape Communications Corporation, for the Netscape Navigator web browser. The engine, code-named SpiderMonkey, is implemented in C. It has since been updated (in JavaScript 1.5) to conform to ECMA-262 Edition 3. The Rhino engine, created primarily by Norris Boyd (formerly of Netscape; now at Google) is a JavaScript implementation in Java. Rhino, like SpiderMonkey, is ECMA-262 Edition 3 compliant.
• Web browser is by far the most common host environment for JavaScript. Web browsers typically use the public API to create "host objects" responsible for reflecting the DOM into JavaScript. The web server is another common application of the engine. A JavaScript webserver would expose host objects representing an HTTP request and response objects, which a JavaScript program could then manipulate to dynamically generate web pages.

Because JavaScript is the only language that the most popular browsers share support for, it has become a target language for many frameworks in other languages, even though JavaScript was never intended to be such a language. Despite the performance limitations inherent to its dynamic nature, the increasing speed of JavaScript engines has made the language a surprisingly feasible compilation target.

jQuery

jQuery is a cross-browser JavaScript library designed to simplify the client-side scripting of HTML. It was released in January 2006 at BarCamp NYC by John Resig. Used by over 49% of the 10,000 most visited websites, jQuery is the most popular JavaScript library in use today.

jQuery is free, open source software, dual-licensed under the MIT License or the GNU General Public License, Version 2. jQuery's syntax is designed to make it easier to navigate a document, select DOM elements, create animations, handle events, and develop Ajax applications. jQuery also provides capabilities for developers to create plug-ins on top of the JavaScript library. This enables developers to create abstractions for low-level interaction and animation, advanced effects and high-level, theme-able widgets. The modular approach to the jQuery framework allows the creation of powerful and dynamic web pages and web applications.

Microsoft and Nokia have announced plans to bundle jQuery on their platforms, Microsoft is adopting it initially within Visual Studio for use within Microsoft's ASP.NET AJAX framework and ASP.NET MVC Framework while Nokia has integrated it into their Web Run-Time widget development platform. jQuery has also been used in MediaWiki since version 1.16.

jQuery contains the following features:

• DOM element selections using the cross-browser open source selector engine Sizzle, a spin-off out of the jQuery project
• DOM traversal and modification (including support for CSS 1-3)
• Events
• CSS manipulation
• Effects and animations
• Ajax
• Extensibility through plug-ins
• Utilities - such as browser version and the each function.
• Cross-browser support

jQuery has two usage styles:

• via the $ function, which is a factory method for the jQuery object. These functions, often called commands, are chainable; they all return jQuery objects
• via $.-prefixed functions. These are utility functions which do not work on the jQuery object per se. Typically, access to and manipulation of multiple DOM nodes begins with the $ function being called with a CSS selector string, which results in a jQuery object referencing matching elements in the HTML page. This node set can be manipulated by calling instance methods on the jQuery object, or on the nodes themselves.

(sources : http://en.wikipedia.org)

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