# Setting Up Your First Node.js Application Step-by-Step

## Overview

Node.js allows us to run JavaScript outside the browser. It is built on Chrome’s V8 JavaScript engine and is mainly used for backend development, APIs, real-time apps, and automation tools.

Before building applications with Node.js, it is important to understand how to install it, run JavaScript files, and use the Node runtime properly.

### Installing Node.js

To install [Node.js](https://nodejs.org/en/download), go to the official website of Node.js and download the LTS (Long Term Support) version.

The installation process is mostly the same for all operating systems:

*   Download the installer
    
*   Run the setup
    
*   Keep the default options
    
*   Finish installation
    

Node.js also installs **npm (Node Package Manager)** automatically, which is used to install packages later.

### Checking the Installation

After installation, open your terminal or command prompt and run:

```plaintext
node -v
```

This shows the installed Node.js version.

Example:

```plaintext
v24.1.0
```

Now check npm:

```plaintext
npm -v
```

If both commands return versions, Node.js is installed correctly.

### Understanding Node REPL

Before writing actual files, Node.js provides something called the **REPL**.

REPL stands for:

*   **Read**
    
*   **Evaluate**
    
*   **Print**
    
*   **Loop**  
    

It is an interactive environment where we can write JavaScript directly in the terminal and instantly see the output.

Start the REPL using:

```plaintext
node
```

Now you can write JavaScript:

```plaintext
2 + 2
```

Output:

```plaintext
4
```

Another example:

```plaintext
const name = "Pallab";
console.log(name);
```

The REPL is useful for testing small snippets quickly without creating files.

To exit the REPL:

```plaintext
.exit
```

### Creating Your First JavaScript File

Now let’s create a real JavaScript file.

Create a file named:

```plaintext
app.js
```

Inside the file write:

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

Save the file.

### Running a Script Using Node

Open the terminal in the same folder where the file exists and run:

```plaintext
node app.js
```

Output:

```plaintext
Hello from Node.js
```

Here, Node.js takes the JavaScript file, executes it inside the runtime, and prints the output in the terminal.

### Node Execution Flow

```plaintext
JavaScript File
       ↓
Node Runtime
       ↓
V8 Engine Executes Code
       ↓
Output in Terminal
```

This is the basic execution flow of Node.js.

### Writing Your First Hello World Server

Node.js can also create servers using built-in modules.

Create a file named:

```plaintext
server.js
```

Add this code:

```plaintext
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 it using:

```plaintext
node server.js
```

Now open your browser and visit:

```plaintext
http://localhost:3000
```

You will see:

```plaintext
Hello World
```

### Script to Runtime Flow

```plaintext
server.js
    ↓
Node Runtime Starts
    ↓
HTTP Server Created
    ↓
Listening on Port 3000
    ↓
Browser Sends Request
    ↓
Server Sends Response
```

### Conclusion

Node.js makes it possible to run JavaScript outside the browser. After installing it, we can use the REPL for quick testing, execute JavaScript files using the `node` command, and even create servers with built-in modules.

These are the core basics every Node.js developer should understand before moving into frameworks and backend development.