Apart from being used in the browser, JavaScript is also used in backend e.g. using [Node.js](https://nodejs.org/) or [Deno](https://deno.land/) for writing server-side code in JavaScript.
If you pick up JavaScript for the Backend, my personal recommendation would be to learn [JavaScript](/javascript) and then go with [Node.js](/nodejs) as it is the most popular and widely used option. Also, I would recommend learning TypeScript later on as you continue with your backend development Journey; it's a superset of JavaScript and is used in many projects.