Setting Up Your First Node.js Application

Installing Node.js

1. Go to the official site: https://nodejs.org

2. Download the LTS (Long Term Support) version

3. Install with default settings (works for Windows, macOS, Linux)

OS-neutral tip:

• If you can open a terminal/command prompt, you’re good to go

• Installer automatically sets up everything

Checking Installation (Terminal)

Open terminal / command prompt and run:

node -v

You should see something like:

v20.x.x

Also check npm:

npm -v

Understanding Node REPL

REPL = Read → Evaluate → Print → Loop

It’s an interactive environment where you can run JavaScript line-by-line.
Start it:

node

Now you’ll see:

>

Try writing 2+3 in javascript:

Output:

5

What’s happening:

You type → Node reads → runs it → prints result → waits again

Exit REPL:

.exit

Creating Your First JavaScript File

Create an app.js file and write:

console.log("Hello from Node.js");

Running Script Using Node

In terminal: (write node .js)

node app.js

Output:

Hello from Node.js

Node Execution Flow

File (app.js)
   ↓
Node Runtime
   ↓
Executes JS
   ↓
Output in Terminal

Writing Your First "Hello World" Server

create server.js

const http = require('http');

const server = http.createServer((req, res) => {
  res.send("Hello World");
});

server.listen(3000, () => {
  console.log("Server running on port 3000");
});

Run it:

node server.js

Output:

Server running on port 3000

Open browser: Hit "http://localhost:3000"

You’ll see:

Hello World