Socket.IO runs on Node.js, so you need to install Node.js before creating the application.

Node.js includes npm, which is the package manager used to install project dependencies.

1. Download and install a supported Node.js LTS release.
2. Open your terminal or command prompt.
3. Verify the installation.

The following commands display the installed versions.

node --version
npm --version

Create a dedicated folder for the chat application.

Open your terminal and execute the following commands:

1. Create the project directory.
2. Navigate into the directory.
3. Initialize npm.

The npm init -y command generates a default package.json file.

The package.json file stores project metadata, dependencies, scripts, and module configuration.

mkdir socket-io-chat
cd socket-io-chat
npm init -y

We will use JavaScript ES Modules throughout this tutorial.

ES Modules allow you to use import and export syntax instead of CommonJS require() and module.exports.

Open package.json and add the type property.

The project configuration should look like this:

{
  "name": "socket-io-chat",
  "version": "1.0.0",
  "description": "Real-time chat application using Node.js and Socket.IO",
  "type": "module",
  "scripts": {
    "start": "node src/server.js",
    "dev": "node --watch src/server.js"
  }
}

Now install the packages required by the application.

We need two main dependencies:

• express: Creates the HTTP server application and handles HTTP routes.
• socket.io: Provides real-time event communication.

We will also use dotenv to load environment variables and cors only if we later separate the frontend and backend origins.

For this initial implementation, the frontend will be served by Express from the same origin, so separate CORS configuration is unnecessary.

npm install express socket.io dotenv

Before writing application code, organize the project into separate files.

Create the following structure:

socket-io-chat/
│
├── public/
│   ├── index.html
│   ├── style.css
│   └── app.js
│
├── src/
│   ├── config/
│   │   └── socket.js
│   ├── events/
│   │   └── chat.events.js
│   └── server.js
│
├── .env
├── .gitignore
└── package.json

Responsibilities:

File	Responsibility
server.js	Creates and starts the HTTP server
socket.js	Initializes Socket.IO
chat.events.js	Registers chat-related event handlers
index.html	Defines the chat interface
style.css	Styles the chat interface
app.js	Connects the browser to Socket.IO
.env	Stores environment variables
.gitignore	Excludes sensitive and generated files

This separation makes the project easier to understand and maintain as additional features are introduced.

mkdir -p public src/config src/events

Environment variables allow you to configure application settings without hardcoding them into source files.

Create a .env file in the project root.

Add the following configuration:

PORT=3000
NODE_ENV=development

Create a .gitignore file in the project root.

Add the following entries:

This prevents node_modules, local environment files, and debug logs from being included in Git commits.

node_modules/
.env
.env.*
!.env.example
npm-debug.log*
.DS_Store