REST vs WebSocket

🤔 The Difference

REST (representational state transfer): You ask, the server answers. Like email. WebSocket: You open a connection and both sides can send messages anytime. Like a phone call.

flowchart TB
    subgraph REST[REST - Request/Response]
        direction TB
        R1["Browser: GET /api/data"]
        R2["Server: Here's the data"]
        R3["Browser: POST /api/update"]
        R4["Server: OK, updated"]
    end

    subgraph WebSocket[WebSocket - Persistent Connection]
        direction TB
        W1["Browser opens connection to server"]
        W2["⬆ Browser sends: New message"]
        W3["⬇ Server sends: Live update"]
        W4["⬇ Server sends: Another update"]
        W5["⬆ Browser sends: Typing..."]
    end

    style REST fill:#3b82f6,color:#fff
    style WebSocket fill:#10b981,color:#fff

📋 Comparison

Feature	REST (HTTP)	WebSocket
Model	Request → Response	Persistent connection, two-way
Connection	Opens and closes per request	Stays open
Latency	Higher (new connection each time)	Lower (instant push)
Real-time	❌ Polling needed	✅ Instant
Use cases	CRUD APIs, websites	Chat, games, live updates

🔄 How REST Works

→ GET /api/weather
← 200 OK { "temp": 22, "city": "Mumbai" }

→ POST /api/weather/city
← 201 Created

→ GET /api/weather
← 200 OK { "temp": 23, "city": "Mumbai" }

Each request is independent. The server doesn’t remember you between requests (stateless). To get updates, the client has to ask repeatedly.

🔗 How WebSocket Works

// Client side (JavaScript)
const ws = new WebSocket('wss://chat.example.com');

// Connection opens
ws.onopen = () => {
  ws.send('Hello!');  // Send message
};

// Receive messages anytime
ws.onmessage = (event) => {
  console.log('Got:', event.data);  // "New message: Hey!"
};

One connection. Both sides can send messages anytime.

🗺️ Alternatives: Polling & SSE

Technique	How it works	Best for
Polling	Client asks every few seconds	Simple, quick to implement
Long polling	Server holds the request until data is ready	When updates are infrequent
SSE (Server-Sent Events)	Server pushes to client (one-way)	Notifications, news feeds
WebSocket	Full two-way communication	Chat, gaming, collaborative editing

flowchart LR
    subgraph Methods[Real-Time Communication Methods]
        Poll[Polling<br/>Client asks repeatedly] --> Server1
        SSE[SSE<br/>Server pushes to client] --> Server2
        WS[WebSocket<br/>Two-way persistent] --> Server3
    end

    style Methods fill:#7c3aed,color:#fff
    style Poll fill:#3b82f6,color:#fff
    style SSE fill:#f59e0b,color:#fff
    style WS fill:#10b981,color:#fff

🎯 When to Use What

Use REST for…	Use WebSocket for…
CRUD APIs	Chat applications
Loading page data	Live sports scores
Form submissions	Stock price tickers
Simple queries	Multiplayer games
Mobile app backends	Collaborative editing (Google Docs)

In Simple Words

REST = ask → receive (like HTTP). Each request is separate. Good for standard APIs.
WebSocket = open connection → both sides talk freely. Good for real-time apps.
REST is stateless; WebSocket maintains a persistent stateful connection
Polling fakes real-time by repeatedly asking the server; WebSocket is truly real-time
SSE is one-way (server → client); WebSocket is two-way