Node JS is not a language, it uses JavaScript language as the main programming interface. Node is a desktop application (or runtime environment) that runs JavaScript files. Node runtime can be compared to the JVM Java Virtual Machine or the IDLE Python interpreter.   
Node.js connects the ease of a scripting language (JavaScript) with the power of Unix network programming. Node.js was built on the Google V8 JavaScript engine.   
Node.js is an open-source, cross-platform, JavaScript runtime environment that executes JavaScript code outside of a web browser.   
Written in C, C++, Javascript<br /><br />

NodeJS is mainly C, C++ which does have to be __compiled down a machine code__ and Javascript is used in order to interface it.   