What Is Node.js?

Node.js allows JavaScript to run outside the browser.

It is commonly used for:

• Backend development

• APIs

• Servers

• CLI tools

Step 1: Install Node.js

Download Node.js from:

Node.js Official Website

Install the LTS version.

Step 2: Verify Installation

Open terminal and run:

node -v

Example Output

v22.1.0

Check npm Installation

npm -v

What Is npm?

npm = Node Package Manager

Used to install JavaScript packages.

Step 3: Understanding Node REPL

REPL means:

It is an interactive Node.js console.

Start REPL

node

Example

> 2 + 3

Output

5

Another Example

> console.log("Hello")

Output

Hello

Exit REPL

.exit

or press:

Ctrl + C twice

Step 4: Create Your First JavaScript File

Create a file:

app.js

Add Code

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

Step 5: Run the Script

Open terminal in project folder.

Run:

node app.js

Output

Hello Node.js

Node Execution Flow

Script → Runtime → Output Flow

Step 6: Create Your First Node.js Server

Node.js includes a built-in HTTP module.

Hello World Server

const http = require("http");

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

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

Run Server

node app.js

Output

Server running on port 3000

Open Browser

Visit:

http://localhost:3000

Browser Result

Hello World

How the Server Works

Server Request Flow

Stopping the Server

Press:

Ctrl + C

inside terminal.

Common Beginner Mistakes

Practice Exercise

Create math.js

console.log(10 + 5);

Run File

node math.js

Create Another Server

const http = require("http");

http.createServer((req, res) => {
  res.end("My First Server");
}).listen(4000);

Visit:

http://localhost:4000

Key Takeaways

Final Notes

Your first Node.js application teaches the core workflow:

Write JavaScript
↓
Run with Node.js
↓
See output/server response

This foundation is important before learning:

• Express.js

• APIs

• Databases

• Authentication

• Real-world backend systems