This short guide describes briefly what is NodeJS. Following are some of the references to the definition and explanation of the question What is NodeJS.

Node.js® is a JavaScript runtime built on Chrome’s V8 JavaScript engine.

https://nodejs.org/en/

Node.js is an open-source, cross-platform, JavaScript runtime environment that executes JavaScript code outside of a browser.

https://en.wikipedia.org/wiki/Node.js

Node.js is an open source server environment which runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)

https://www.w3schools.com/nodejs/nodejs_intro.asp

1. NodeJS is not programming language or framework
2. NodeJS is a run-time environment to execute JavaScript code
3. NodeJS is asynchronous which means that it can handle multiple requests at the same time without any delay
4. Core NodeJS modules include OS (Operating System), FS (File System), Events and HTTP
5. Modules are used in NodeJS to organize the code. There are some built-in modules available as well. every file is a module in NodeJS
6. We need to export the variables and methods if we want to use them outside the modules
7. Require function is used to load a module in another module
8. Module wrapper function is automatically added in each module by NodeJS
9. Each wrapper function have access to the local variables like require, module, exports, __filename, __dirname