Express Chat Backend API

A Node.js backend application built with Express and Socket.io, providing authentication and real-time chat functionality.

Tech Stack

• Express.js - Web framework for Node.js
• Socket.io - Real-time bidirectional event-based communication
• TypeScript - Type safety and modern JavaScript features
• MongoDB/Database - Data persistence
• JWT - Authentication tokens

Getting Started

Prerequisites

• Node.js (version 16 or higher)
• npm or yarn package manager
• MongoDB database (local or cloud)

Installation

1. Clone the repository

git clone <repository-url>
cd <project-name>

2. Install dependencies

npm install
# or
yarn install

3. Create environment file

cp .env.example .env

Configure your environment variables in .env:

JWT_SECRET=<jwt_secret>
DB_URL=<mongodb_connection_string>

4. Start the development server

npm run dev
# or
yarn dev

The server will start on http://localhost:5000 by default (no env provided)

Project Structure

src/
├── config/              # Configuration files
│   ├── db.js           # Database connection setup
│   └── environment.js  # Environment variables loader (centralized process.env)
├── controllers/         # Route handlers and business logic
│   ├── authController.js    # Authentication logic (login, register, etc.)
│   ├── chatController.js    # Chat-related API endpoints
│   └── errorHandler.js      # Global error handling middleware
├── middlewares/         # Custom middleware functions
│   └── catchAsync.js   # Async error handling wrapper
├── models/             # Database models/schemas
│   └── userModel.ts    # User data model
├── routes/             # API route definitions
│   ├── authRoutes.js   # Authentication endpoints
│   └── socketio.js     # Socket.io event handlers
└── utils/              # Utility functions and helpers

Environment Variables

Create a .env file in the root directory with the following variables:

JWT_SECRET=<jwt_secret>
DB_URL=<mongodb_connection_string>

Replace the placeholders with your actual values:

• <jwt_secret> - A secure random string for JWT token signing
• <mongodb_connection_string> - Your MongoDB connection URL

Configuration Features:

• Centralized environment loading through config/environment.js
• Costly process.env calls are optimized and cached
• Database connection managed in config/db.js

Available Scripts

• npm run dev - Start development server with hot reload
• npm run build - Build TypeScript to JavaScript
• npm run start - Start production server
• npm run lint - Run ESLint
• npm run test - Run tests

API Endpoints

Authentication Routes

POST /api/auth/register    # User registration
POST /api/auth/login       # User login
POST /api/auth/logout      # User logout
GET  /api/auth/me          # Get current user

Chat Routes

GET  /api/chat/messages    # Get chat messages
POST /api/chat/messages    # Send message

Socket.io Events

Client to Server

• register - Register user with JWT token for online status
• private-message - Send private message to specific user

Server to Client

• unauthorized - Invalid token response
• online_users - Updated list of online users
• private-message - Receive private message from another user
• user_offline - User not available for messaging

Event Details

register

socket.emit('register', jwt_token);

Registers the user with their JWT token to track online status and enable messaging.

private-message

socket.emit('private-message', {
  recipientSocketId: 'socket_id',
  token: 'jwt_token',
  message: 'message_content',
});

Sends a private message to a specific user using their socket ID.

online_users

socket.on('online_users', (users) => {
  // users object contains: { userId: { name, socketId, role } }
});

Receives updated list of all online users with their details.

private-message (received)

socket.on('private-message', (data) => {
  // data: { sender: userId, message: content, timestamp: ISO_string }
});

Receives a private message from another user.

Features

• Authentication - JWT-based user authentication
• Real-time Chat - Live messaging with Socket.io
• Error Handling - Centralized error management
• Type Safety - TypeScript support for models
• Async Handling - Proper async/await error catching
• Database Integration - MongoDB connection and models
• CORS Support - Cross-origin resource sharing
• Environment Management - Optimized environment variable handling

Architecture

Error Handling

• Global error handler in controllers/errorHandler.js
• Async wrapper middleware catchAsync for route handlers
• Consistent error response format

Database

• Connection setup in config/db.js
• TypeScript models for type safety
• User model with authentication features

Socket.io Integration

• Real-time event handling in routes/socketio.js
• Room-based chat functionality
• Connection management and user presence

Development

The project follows a modular structure with clear separation of concerns:

• Config: Environment and database setup
• Controllers: Business logic and request handling
• Middlewares: Reusable middleware functions
• Models: Data structures and database schemas
• Routes: API endpoints and Socket.io events
• Utils: Helper functions and utilities