Your First Node.js Script and the REPL

The fastest way to understand Node.js is to run some code. This lesson shows you how to execute scripts and use the interactive REPL before writing any project code.

Installing Node.js

If you haven’t already, install Node.js from nodejs.org. Choose the LTS version. Verify the installation:

node --version   # v20.x or higher
npm --version    # 10.x or higher

The REPL

Node.js includes an interactive shell called the REPL (Read-Eval-Print Loop). Run it with just node:

node

You get a > prompt. Type any JavaScript:

> 2 + 2
4
> const name = 'Bulletin'
undefined
> `Hello from ${name}`
'Hello from Bulletin'
> process.version
'v20.x.x'
> .exit

The REPL is for quick experiments. Notice process — that’s a global Node.js object that doesn’t exist in browsers.

Your first script

Create a file hello.js:

const message = 'Hello from Node.js'
console.log(message)
console.log('Node version:', process.version)
console.log('Current directory:', process.cwd())

Run it:

node hello.js

Output:

Hello from Node.js
Node version: v20.x.x
Current directory: /your/current/directory

That’s it. No browser, no HTML, no index.html — just JavaScript executing directly.

Differences from browser JavaScript

Some things you expect from browser JS don’t exist in Node.js:

Browser	Node.js
window	global (or globalThis)
document	Not available
localStorage	Not available
fetch	Available (Node 18+)
process	Not available in browser
require()	Available (CommonJS)
__dirname	Available (CommonJS)

And some things Node.js has that browsers don’t:

• process — access to the running process, environment variables, arguments
• fs module — read and write the file system
• path module — work with file paths across operating systems
• http module — create raw HTTP servers

Passing arguments

Node.js exposes command-line arguments via process.argv:

args.js

console.log(process.argv)

node args.js hello world
# ['node', '/path/to/args.js', 'hello', 'world']

process.argv[0] is node, process.argv[1] is the script path, and arguments start at index 2.

Exercise

1. Open the REPL and explore: try Object.keys(process) to see what’s on the process object.
2. Create greet.js that takes a name from process.argv[2] and prints Hello, [name]!. If no argument is passed, print Hello, stranger!.
3. Run it: node greet.js Alice → Hello, Alice! and node greet.js → Hello, stranger!

Recap

• Install Node.js LTS; verify with node --version.
• The REPL (node with no arguments) is a quick scratchpad for experiments.
• Run scripts with node filename.js.
• process is a Node.js global: it has version, cwd(), argv, and much more.
• Browser globals like window, document, and localStorage don’t exist in Node.js.