JavaScript (JS) is a dynamic computer programming language. It is most commonly used as part of Web browsers, whose implementations allow client-side scripts to interact with the user, control the browser, communicate asynchronously, and alter the document content that is displayed. It is also used in server-side network programming with runtime environments such as Node.js, game development and the creation of desktop and mobile applications. With the rise of the single-page Web app and JavaScript-heavy sites, it is increasingly being used as a compile target for source-to-source compilers from both dynamic languages and static languages. In particular,Emscripten and highly optimised JIT compilers, in tandem with asm.js that is friendly to AOT compilers likeOdinMonkey, have enabled C and C++ programs to be compiled into JavaScript and execute at near-native speeds, making JavaScript be considered the "assembly language of the Web", according to its creator and others.

(Source: Wikipedia) 

JavaScript was originally developed by Brendan Eich, while working for Netscape Communications Corporation. While competing with Microsoft for user adoption of Web technologies and platforms, Netscape considered their client-server offering a distributed OS with a portable version of Sun Microsystems' Java providing an environment in which applets could be run. Because Java was a competitor of C++ and aimed at professional programmers, Netscape also wanted a lightweight interpreted language that would complement Java by appealing to nonprofessional programmers, like Microsoft's Visual Basic. 

Although it was developed under the name Mocha, the language was officially called LiveScript when it first shipped in beta releases of Netscape Navigator 2.0 in September 1995, but it was renamed JavaScript. when it was deployed in the Netscape browser version 2.0B3.

The change of name from LiveScript to JavaScript roughly coincided with Netscape adding support for Java technology in its Netscape Navigator Web browser. The final choice of name caused confusion, giving the impression that the language was a spin-off of the Java programming language, and the choice has been characterized as a marketing ploy by Netscape to give JavaScript the cachet of what was then the hot new Web programming language.

(Source: Wikipedia)