Node.js is an open-source MIT licensed cross-platform environment for JavaScript, which allows users to execute JS code outside the browser. It has been written in JavaScript, C, and C++. It can be installed on Windows, macOS X, Smart OS, and Linux.
It allows using JavaScript to develop command-line tools. It allows running scripts on the server-side for producing dynamic pages. Rather than using different server-side and client-side languages, it helps you to unify your web application around single programming.