# 🚀 Simple Node.js Hello World (with Docker & Environment Variables)

Welcome to this beginner-friendly guide! This project is a "Hello World" web application built using **Node.js** and **Express**. It is designed to be easily configurable using a `.env` file and ready to run inside a **Docker** container.

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## 🛠 Prerequisites

Before you begin, ensure you have the following installed on your computer:
1. **[Node.js](https://nodejs.org/)** (Version 18 or higher recommended)
2. **[Docker](https://www.docker.com/products/docker-desktop/)** (To run the application in a container)
3. **A Code Editor** (Like [VS Code](https://code.visualstudio.com/))

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## 📁 Project Structure Explained

Here is what's inside this project and what each file does:

- `index.js`: The "brain" of our app. It handles web requests and sends back a message.
- `.env`: A configuration file for "secrets" or settings (like which port to use).
- `package.json`: A manifest file that lists the libraries our app needs to work.
- `Dockerfile`: A set of instructions for Docker on how to "package" this app into a container.
- `.dockerignore` / `.gitignore`: Files that tell Docker and Git which files to ignore (like `node_modules` which can be very large).

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## ⚙️ How to Configure

You can change how the app behaves without touching the code! Open the `.env` file:

```env
PORT=3000
MESSAGE="Hello from Node.js with .env!"
```

- **PORT**: The "doorway" the app uses to listen for visitors. (Default: 3000)
- **MESSAGE**: The text that will appear when you visit the app in your browser.

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## 🏃 Method 1: Running Locally (Without Docker)

Use this method if you just want to test the app quickly on your machine.

1. **Open your terminal** (Command Prompt, Terminal, or PowerShell).
2. **Navigate to the project folder**:
   ```bash
   cd hello-world-node
   ```
3. **Install dependencies**:
   ```bash
   npm install
   ```
4. **Start the app**:
   ```bash
   npm start
   ```
5. **View the app**: Open your browser and go to `http://localhost:3000`.

---

## 🐳 Method 2: Running with Docker (Recommended)

Docker packages the app so it runs exactly the same way on every computer.

### Step 1: Build the Image
This creates a "package" of your application.
```bash
docker build -t hello-world-node .
```

### Step 2: Run the Container
This starts the "package" and makes it live.
```bash
docker run -d -p 3000:3000 --env-file .env --name my-hello-app hello-world-node
```
*Note: `-d` runs it in the background, `-p 3000:3000` maps your computer's port to the container's port.*

### Step 3: See it in action
Open your browser and visit `http://localhost:3000`.

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## 🧹 Cleaning Up

If you want to stop the Docker container:

1. **Stop the container**:
   ```bash
   docker stop my-hello-app
   ```
2. **Remove the container**:
   ```bash
   docker rm my-hello-app
   ```
3. **Remove the image** (optional):
   ```bash
   docker rmi hello-world-node
   ```

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## ❓ Troubleshooting

- **Port already in use**: If you see an error about port 3000, change the `PORT` in your `.env` file or stop any other apps running on that port.
- **Docker not running**: Make sure the Docker Desktop app is open and running.
- **Can't find `npm`**: Ensure Node.js is installed correctly and added to your system's PATH.

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