What is Node.js?

As you learned in Chapter 2, The State of JavaScript, Node.js is "JavaScript on the server". Before we move forward, let's delve a little deeper into understanding what that means.

Traditionally, JavaScript is interpreted by a JavaScript engine that converts JavaScript code into more optimized, machine-executable code, which then gets executed. The engine interprets the JavaScript code at the time it is run. This is unlike compiled languages such as C#, which must first be compiled into an intermediate language (IL), where this IL is then executed by the common language runtime (CLR), software similar in function to the JavaScript engine.

Technically, it is inaccurate to classify a language as interpreted or compiled—how a language is processed depends on the implementation. Someone can build a compiler that converts JavaScript into machine code and run it; in that instance, JavaScript would be a compiled language.

 However, since JavaScript is almost always interpreted by a JavaScript engine, you'll often hear people refer to JavaScript as an interpreted language.

Different browsers use different JavaScript engines. Chrome uses V8, Firefox uses SpiderMonkey, WebKit browsers such as Safari use JavaScriptCore, and Microsoft Edge uses Chakra. Node.js uses V8 as its JavaScript engine and adds C++ bindings that allow it to access operating system resources, such as files and networking.

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