About JavaScript

What is JavaScript?

JavaScript® is the Netscape-developed object scripting language used in millions of web pages and server applications worldwide. Netscape's JavaScript is a superset of the ECMA-262 Edition 3 (ECMAScript) standard scripting language, with only mild differences from the published standard.

Contrary to popular misconception, JavaScript is not "Interpretive Java". In a nutshell, JavaScript is a dynamic scripting language supporting prototype based object construction. The basic syntax is intentionally similar to both Java and C++ to reduce the number of new concepts required to learn the language. Language constructs, such as if statements, for and while loops, and switch and try ... catch blocks function the same as in these languages (or nearly so.)

JavaScript can function as both a procedural and an object oriented language. Objects are created programmatically in JavaScript, by attaching methods and properties to otherwise empty objects at run time, as opposed to the syntactic class definitions common in compiled languages like C++ and Java. Once an object has been constructed it can be used as a blueprint (or prototype) for creating similar objects.

JavaScript's dynamic capabilities include runtime object construction, variable parameter lists, function variables, dynamic script creation (via eval), object introspection (via for ... in), and source code recovery (JavaScript programs can decompile function bodies back into their source text)

Intrinsic objects are Number, String, Boolean, Date, RegExp, and Math.

For a more in depth discussion of JavaScript programming follow the JavaScript resources links below.

What JavaScript implementations are available?

mozilla.org hosts two JavaScript implementations. The first ever JavaScript was created by Brendan Eich at Netscape, and has since been updated (in JavaScript 1.5) to conform to ECMA-262 Edition 5. This engine, code named SpiderMonkey, is implemented in C. The Rhino engine, created primarily by Norris Boyd (also at Netscape) is a JavaScript implementation in Java. Like SpiderMonkey, Rhino is ECMA-262 Edition 3 compliant.

Several optimizations such as TraceMonkey (Firefox 3.5), JägerMonkey (Firefox 4) and IonMonkey were added to the SpiderMonkey JavaScript engine from time to time.

Besides the above implementations, there are other popular JavaScript engines such as:-

  • Google's V8, which is used in the Google Chrome browser.
  • The JavaScriptCore (SquirrelFish/Nitro) used in some WebKit browsers such as Apple Safari.
  • Carakan in Opera.

The Chakra engine used in Internet Explorer is technically a JScript engine, rather than a JavaScript engine.

Each mozilla.org JavaScript engine exposes a public API applications can call on for JavaScript support. By far, the most common host environment for JavaScript is web browsers. Web browsers typically use the public API to create 'host objects' responsible for reflecting the DOM into JavaScript.

Another common application for JavaScript is as a (web) server side scripting language. A JavaScript web server would expose host objects representing a HTTP request and response objects, which could then be manipulated by a JavaScript program to dynamically generate web pages.

For more information on embedding JavaScript in your own applications, follow either the SpiderMonkey or Rhino links below, or visit us on the netscape.public.mozilla.jseng newsgroup.

JavaScript resources

Information specific to JavaScript in C engine (aka SpiderMonkey) embedding.
Information specific to the JavaScript implementation written in Java (aka Rhino).
Language resources
Pointers to published JavaScript standards, LiveConnect documents, and work on JavaScript 2.0.
Tamarin Project
Information on the the high-performance, open-source virtual machine for JavaScript 2.0.
A re-introduction to JavaScript
JavaScript Guide and JavaScript Reference
Scripting resources
Pointers to JavaScript scripting resources, including recommended reading, online references and tutorials, and sample code.
Projects page
Lists other projects using the open source JavaScript engines.
Test library page
Information about JavaScript test suite.
The newsgroup for discussion about the JavaScript engines.
The newsgroup for general discussion about ECMAScript, mostly (though not necessarily) as it pertains to browsers.

JavaScript is a trademark or registered trademark of Oracle in the U.S. and other countries.

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Last updated by: Sheppy,