Node.js is a tool that lets JavaScript run outside a web browser. Developers use it to build things such as web servers, command-line tools, and scripts that work with files.
JavaScript often runs inside a browser to make web pages interactive. Node.js provides a different place for the same language to run, much like using one kind of recipe in two different kitchens.
Node.js is not a programming language on its own; it is the environment that runs JavaScript. A project may need it to start, test, or build its code.