EventSource: The under appreciated sibling of WebSockets – Benedicte Emilie Brækken - NDC Oslo 2024

EventSource/Server-Sent Events (SSE) is a simpler alternative to WebSockets for one-way server-to-client real-time communication

EventSource has better scalability than polling since it maintains a single open connection and doesn’t require constant new requests

Main EventSource advantages:

• Built-in reconnection handling
• Native browser support
• Works over regular HTTP
• Simple implementation
• Event parsing handled by browser

WebSockets create a completely new protocol connection, while EventSource uses standard HTTP

Key differences between WebSocket and EventSource:

• WebSocket is bidirectional, EventSource is one-way (server to client)
• WebSocket requires special server infrastructure
• EventSource works with standard HTTP servers
• WebSocket has more complex implementation

HTTP/2 improvements like multiplexing and server push make EventSource more efficient

For one-way server-to-client communication, EventSource is often a better choice than WebSocket due to simplicity

EventSource limitations:

• Can’t send client-to-server data (one-way only)
• Limited header customization
• No binary data support

Implementation requires only ~20 lines of JavaScript on both client and server sides

Works well with distributed systems since it uses standard HTTP infrastructure