🚀 Socket.io Notifications System

Real-time notification delivery with persistent storage & unread state tracking.

This project implements a real-time notification system using Node.js, Express, and Socket.io, with notifications stored in a MongoDB so the user can still retrieve notifications even when offline.

It supports:

• ✅ User → Socket mapping
• ✅ Real-time delivery
• ✅ Pending / Delivere tracking
• ✅ Persistent notification history
• ✅ Works across multiple browser tabs & devices

Notifications are:

1. Stored in DB
2. Delivered instantly if the user is online
3. Delivered later when the user reconnects

---

📦 Installation & Setup

git clone https://github.com/nomanaslam1696/Socket.io-Notifications-System.git
cd Socket.io-Notifications-System
npm install

Create .env file

PORT=3000
MONGODB_URI=mongodb://localhost:27017/notifications

Start Server

npm run dev

🌐 API Endpoints

1. Send Notification Endpoint to send a notification to a specific user.

POST /api/notifications/send

Body

{
  "user_id": "USER_ID",
  "message": "Your order #12345 has been confirmed."
}

Response

{
  "success": true,
  "message": "Notification sent and stored."
}

2. Get User Notifications Fetch stored notifications (delivered/pending).

GET /api/notifications/:user_id

Response

[
  {
    "id": "abc123",
    "title": "Order Placed!",
    "message": "Your order #12345 has been confirmed.",
    "is_read": false,
    "timestamp": "2025-10-30T12:00:00Z"
  }
]

🧠 Core Logic Highlights Store user socket connections

const userSockets = new Map();

When user connects

socket.on("register_user", (userId) => {
  userSockets.set(userId, socket.id);
});

Send real-time notification if online

if (userSockets.has(receiver_id)) {
  io.to(userSockets.get(receiver_id)).emit("send_notification", notification);
}

Always store in DB

await NotificationModel.create(notificationData);

🏁 Client Side Example

import io from "socket.io-client";
const socket = io("http://localhost:3000");

socket.emit("register_user", USER_ID);

socket.on("send_notification", (data) => {
  console.log("🔔 New Notification:", data);
});

🧪 Testing the System Open two browser windows

Login with two different user IDs

Trigger notification using POST API

Watch real-time delivery 💨

📌 Key Benefits Works even when user reconnects later 🌙

Notifications are always stored 🗄️

Real-time updates without refreshing 🔁

Lightweight & scalable ⚡

👨‍💻 Author

Noman Aslam

Node.js Backend Developer.