When people first hear about Node.js, they usually think:

“It lets JavaScript run outside the browser.”

And that’s exactly what it does.

Node.js is a JavaScript runtime that allows you to:

• build servers

• create APIs

• work with files

• build backend applications

Before building large applications, it’s important to understand how a basic Node.js setup works from the ground up.

This article walks through:

• installing Node.js

• verifying installation

• understanding the Node REPL

• running JavaScript files

• creating your first server

without using any frameworks.

---

What Is Node.js?

Normally, JavaScript runs inside browsers.

Example:

• Chrome

• Firefox

• Edge

Node.js allows JavaScript to run directly on your computer using the V8 JavaScript engine.

This means JavaScript can now:

• access files

• create servers

• interact with operating system resources

That’s what makes backend development possible with JavaScript.

---

Installing Node.js

The easiest way to install Node.js is from the official website.

Node.js Official Website

You’ll usually see:

• LTS (Long Term Support)

• Current version

For beginners, LTS is generally preferred because it is more stable.

---

What Gets Installed?

Installing Node.js usually installs:

• Node.js runtime

• npm (Node Package Manager)

npm is used later for installing libraries and packages.

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Checking the Installation

After installation, open your terminal and run:

node -v

Example output:

v24.15.0

This confirms Node.js is installed successfully.

---

Checking npm

You can also verify npm:

npm -v

Example:

11.11.0

---

Understanding the Node REPL

Before creating files, Node.js provides something called:

REPL

REPL stands for:

• Read

• Evaluate

• Print

• Loop

It is an interactive environment where you can run JavaScript directly from the terminal.

---

Starting the REPL

Run:

node

You’ll see something like:

>

Now you can execute JavaScript instantly.

Example:

2 + 2

Output:

4

---

Why the REPL Exists

The REPL is useful for:

• quick testing

• experimenting

• debugging small snippets

• learning JavaScript behavior

Instead of creating files every time, you can test code immediately.

---

Exiting the REPL

You can exit using:

.exit

or:

Ctrl + C

twice.

---

Creating Your First JavaScript File

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

Create a file named:

app.js

Inside it:

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

---

Running the Script

Inside the terminal, run:

node app.js

Output:

Hello Node.js

---

What Actually Happened?

Flow:

app.js
↓
Node.js runtime reads file
↓
JavaScript executes
↓
Output printed in terminal

Node.js acts as the environment executing your JavaScript code.

---

Understanding the node Command

This command:

node app.js

basically tells Node.js:

“Execute this JavaScript file.”

Unlike browsers, Node.js runs code directly on your machine.

---

Writing Your First Node.js Server

Now let’s create a basic HTTP server.

Replace your code with:

const http = require("http");

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

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

---

Running the Server

Run:

node app.js

Output:

Server running on port 3000

Now open:

http://localhost:3000

You’ll see:

Hello from Node.js server

---

Understanding What Happened

Let’s break it down.

---

Step 1: Import HTTP Module

const http = require("http");

Node.js includes built-in modules for backend functionality.

The http module helps create web servers.

---

Step 2: Create Server

http.createServer()

This creates a server capable of handling browser requests.

---

Step 3: Handle Requests

(req, res) => {}

• req → incoming request

• res → outgoing response

Whenever someone visits the server, this function runs.

---

Step 4: Send Response

res.end("Hello from Node.js server");

This sends data back to the browser.

---

Step 5: Start Listening

server.listen(3000)

This starts the server on port 3000.

Now Node.js continuously waits for incoming requests.

---

What Is localhost?

localhost refers to:

• your own computer

• local development machine

Example:

http://localhost:3000

means:

“Access port 3000 on this machine.”

---

Simple Mental Model

Think of Node.js like this:

JavaScript File

“Instructions.”

---

Node Runtime

“Engine executing those instructions.”

---

HTTP Server

“Program waiting for browser requests.”

---

Full Flow

Browser request
↓
Node.js server receives request
↓
Request handler executes
↓
Response sent back
↓
Browser displays output

---

Your first Node.js application is actually very small:

• install Node.js

• write a JavaScript file

• execute it using Node

• optionally create an HTTP server

But this tiny setup is the foundation for:

• APIs

• backend systems

• real-time apps

• full-stack applications

The most important realization is:

Node.js is simply JavaScript running outside the browser with access to backend capabilities.

Once you understand:

• the runtime

• the REPL

• script execution

• server creation

the entire Node.js ecosystem becomes much easier to learn.