Introduction

If you want to start backend development with JavaScript, the first thing you need is Node.js.

Node.js allows JavaScript to run outside the browser. Instead of executing code in Chrome or Firefox, Node.js executes JavaScript directly on your computer or server.

That means you can:

• Build backend APIs

• Create web servers

• Work with files

• Build CLI tools

• Automate tasks

• Create full-stack applications

In this article, you’ll learn how to:

• Install Node.js

• Verify installation

• Understand the Node REPL

• Create your first JavaScript file

• Run Node scripts

• Build a simple Hello World server

By the end, you’ll have your first Node.js application running successfully.

What is Node.js?

Node.js is a JavaScript runtime environment built on Chrome’s V8 JavaScript engine.

Normally, JavaScript runs inside browsers.
Node.js makes it possible to run JavaScript on your operating system directly.

How Node.js Executes Code

Here’s the basic execution flow:

JavaScript File
       │
       ▼
Node.js Runtime
       │
       ▼
V8 Engine Compiles Code
       │
       ▼
Execution Happens
       │
       ▼
Output Appears in Terminal

Installing Node.js

To install Node.js:

1. Visit the official website:

   Node.js Official Website

2. Download the LTS (Long Term Support) version.

The LTS version is recommended for beginners because it is:

• Stable

• Well-tested

• Widely supported

Installation Steps (OS-Neutral)

The installation process is mostly similar across operating systems:

Step 1: Download Installer

Download the installer for your operating system.

Step 2: Run Installer

Open the downloaded installer and continue with default settings.

Step 3: Finish Installation

Once completed, Node.js and npm will both be installed automatically.

What is npm?

npm stands for:

Node Package Manager

It helps you install libraries and tools for Node.js projects.

When Node.js installs, npm comes included automatically.

Checking Node.js Installation

After installation, open your terminal or command prompt.

Run:

node -v

You should see something like:

v22.3.0

Now check npm:

npm -v

Example output:

10.8.1

If both commands work, Node.js is installed correctly.

Understanding the Node REPL

Before creating files, it’s important to understand the Node REPL.

REPL stands for:

Read → Evaluate → Print → Loop

It is an interactive environment where Node.js executes JavaScript line by line.

Starting the REPL

Open terminal and type:

node

You’ll see something like:

>

Now you can write JavaScript directly.

Example:

2 + 3

Output:

5

Another example:

const name = "Subransu"
console.log(name)

Output:

Subransu

How REPL Works Internally

You Type Code
       │
       ▼
Node Reads Input
       │
       ▼
Code Gets Evaluated
       │
       ▼
Result Gets Printed
       │
       ▼
REPL Waits Again

That repeating cycle is why it’s called REPL.

Exiting the REPL

To exit:

.exit

Or press:

Ctrl + C (twice)

Creating Your First JavaScript File

Now let’s create an actual Node.js program.

Create a folder anywhere on your computer:

my-first-node-app

Inside it, create a file:

app.js

Writing Your First Program

Open app.js and add:

console.log("Hello World")

Save the file.

Running a Node.js Script

Open terminal inside the project folder.

Run:

node app.js

Output:

Hello World

Congratulations 🎉

You just executed your first Node.js application.

Understanding What Happened

Let’s break the process down:

app.js
  │
  ▼
node app.js
  │
  ▼
Node Runtime Starts
  │
  ▼
JavaScript Executes
  │
  ▼
console.log() Prints Output

Creating Your First HTTP Server

Now let’s build a simple web server using only Node.js core modules.

Replace the content of app.js with:

const http = require("http")

const server = http.createServer((req, res) => {
  res.write("Hello from Node.js Server")
  res.end()
})

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

Understanding the Code

Importing HTTP Module

const http = require("http")

Node.js provides built-in modules.

The http module helps create web servers.

Creating the Server

http.createServer()

This creates an HTTP server.

The callback runs whenever a request reaches the server.

Request and Response Objects

(req, res)

• req contains request information

• res sends response back to client

Sending Response

res.write("Hello from Node.js Server")

This sends text to the browser.

Ending Response

res.end()

This completes the response cycle.

Without this, the browser keeps waiting.

Starting the Server

server.listen(3000)

This starts the server on port 3000.

Running the Server

Run:

node app.js

Output:

Server running on port 3000

Now open your browser and visit:

http://localhost:3000

You’ll see:

Hello from Node.js Server

Server Request Flow Diagram

Browser Request
       │
       ▼
localhost:3000
       │
       ▼
Node.js Server Receives Request
       │
       ▼
Callback Function Executes
       │
       ▼
Response Sent Back
       │
       ▼
Browser Displays Output

Difference Between Browser JavaScript and Node.js

Browser JavaScript	Node.js
Runs inside browser	Runs on operating system
Uses DOM APIs	Uses system APIs
Cannot access filesystem directly	Can access files and OS
Mainly frontend	Mainly backend

Common Beginner Mistakes

1. Node Command Not Found

This usually means:

• Node.js is not installed

• Terminal restarted incorrectly

• PATH variable missing

Reinstall Node.js if needed.

2. Wrong File Name

Running:

node app.js

requires the file to actually exist.

Check spelling carefully.

3. Port Already in Use

If port 3000 is busy:

server.listen(5000)

Use another port.

Why Learning Core Node.js Matters

Many beginners jump directly into frameworks like Express.

But understanding core Node.js helps you learn:

• How servers work

• Request-response cycle

• Runtime behavior

• Backend fundamentals

• Event-driven architecture

Frameworks become much easier afterward.

Final Project Structure

my-first-node-app/
│
├── app.js

Simple, clean, and enough to start learning Node.js.

Final Thoughts

Your first Node.js application is more than just “Hello World.”

You learned:

• How Node.js works

• How JavaScript runs outside browsers

• What REPL means

• How to execute scripts

• How to create a basic HTTP server

These fundamentals form the base of backend development with JavaScript.

Once you understand these concepts clearly, moving into Express.js, APIs, databases, and full-stack development becomes much easier.

Happy coding 🚀