NodeJS is a run-time environment for JavaScript. With the aid of special engine you can run your JS code on your computer.

You need to install node and npm to run JavaScript on the server.

After you've installed above two packages, you can run your code e.g. by typing node filename.js in your terminal. Make sure you're in the directory where is the particular file.

index.js:

const firstName = 'John'
const lastName = 'Doe'

console.log('Full name: ' + firstName + ' ' + lastName) // Full name: John Doe