The Need for Real-Time
Traditional HTTP follows a request-response pattern where the client must initiate communication. But modern web applications often need server-pushed updates for features like:
Live Chat
Instant message delivery without page refresh
Stock Tickers
Continuous price updates in financial apps
Live Feeds
Sports scores, news updates, social media
Two Approaches to Real-Time
Server-Sent Events (SSE)
HTTP-based, server-to-client streaming
How It Works
Client opens a persistent HTTP connection. Server can push multiple events over this single connection.
Key Characteristics
- Unidirectional (server → client)
- Text-based protocol (easy to debug)
- Automatic reconnection
- Built into browsers (EventSource API)
Example Use Cases
- Live news feeds
- Stock price updates
- Social media notifications
- Dashboard metrics
WebSockets
Full-duplex, bidirectional communication
How It Works
After initial HTTP handshake, upgrades to persistent WebSocket connection allowing both sides to send messages anytime.
Key Characteristics
- Bidirectional (client ↔ server)
- Binary and text data support
- Lower latency than HTTP
- More complex to implement
Example Use Cases
- Chat applications
- Multiplayer games
- Collaborative editing
- Real-time trading platforms
Head-to-Head Comparison
| Feature | SSE | WebSockets |
|---|---|---|
| Direction | Unidirectional (server → client) | Bidirectional (client ↔ server) |
| Protocol | HTTP (text/event-stream) | WebSocket (ws:// or wss://) |
| Data Format | Text only | Text and binary |
| Reconnection | Automatic | Manual implementation needed |
| Browser Support | All modern browsers | All modern browsers |
| Complexity | Simple to implement | More complex protocol |
Interactive Demo
See the difference in action. Click the buttons to simulate message flow.
SSE Simulation
Waiting for server events...
WebSocket Simulation
Connection not established...
When to Use Each
Choose SSE when...
- You only need server-to-client updates
- You want a simple implementation
- Text data is sufficient
- You need automatic reconnection
- You're working with HTTP-only infrastructure
Choose WebSockets when...
- You need true bidirectional communication
- You need to send binary data
- Lowest possible latency is critical
- You're building interactive applications
- You can handle more complex implementation