Basic of JavaScript

• JavaScript (JS) is lightweight, interpreted , object-oriented language with first-class functions and is best known as the scripting language for web pages , but its, used in many non-browser environment multi-paradigm Scripting language that is dynamic and supports object-oriented , imperative , and functional programming styles.
• JavaScript is not "interpreted 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 to new concept required to learn the language construct , such as if statement , for and which loops. and switch and try block function the same as in these language 
• Object are created programmatically in JavaScript. By attaching methods and properties to otherwise empty object at runtime as opposed to the Syntactic class definitions common in compiled language like C++ and Java once an object has been constructed it can be used as ball point (Prototype) for creating similar object.
• JavaScript dynamic capabilities include runtime object construction, Variable , Parameter , list , function variable , dynamic introspection (via for...........in), and source code recovery JavaScript program can decompile function bodies back into their source text.

What JavaScript implementations are available ?

The Mozilla project provides two JavaScript implementations. The first ever JavaScript was created by Brenden Eich at Net Scape, and has since been updated to conform to ECMA-262 Edition 5 and later versions. This engine , code named Spider Monkey is implemented in C/C++ the Rhino engine , created primarily by Norris Boycl (also at Netscape) is JavaScript implementation written in Java like Spider Monkey ,Rhino is ECMA-262 Edition 5 Compliant.

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

• Google V8 which is used in the google chrome browser and recent versions of opera browser. This is also engine used by Nodes Js.
• The JavaScript core (Squirre Fish/nitro) used in some webkit browser such as Apple safari.
• Carakar is old version of opera 
• The chakra engine used in internet explorer ( although the language it implements is formally called JavaScript in Order to avoid trademark issued.