Server Sent Events (SSE)

🚨 𝗧𝗵𝗲 𝗽𝗿𝗼𝗯𝗹𝗲𝗺

Your web app needs real-time updates like stock prices, chat messages, and live scores, but you only need data flowing one direction - from server to client. WebSockets are bidirectional and more complex than needed, while polling wastes bandwidth with constant "anything new?" requests.

💡 𝗪𝗵𝗮𝘁 𝗶𝘀 𝗦𝗦𝗘?

A simple HTTP-based protocol where the server keeps a connection open and pushes text data to the client whenever it wants. Think of it as a one-way WebSocket that's built on standard HTTP.

⚙️ 𝗛𝗼𝘄 𝗶𝘁 𝘄𝗼𝗿𝗸𝘀?

Client opens connection: new EventSource('/events')

Server responds with Content-Type: text/event-stream and keeps connection alive

Server pushes data in simple format:

data: {"price" : 142.50, "symbol" : "AAPL"}
data: {"price" : 143.10, "symbol" : "AAPL"}

Client receives events via

eventSource.onmessage = (event) => { ... }

👍 𝗚𝗿𝗲𝗮𝘁 𝗳𝗶𝘁 𝗳𝗼𝗿

• Live dashboards (metrics, analytics updates)
• News feeds and social media timelines (10 new posts since you loaded the page)
• Stock tickers and financial data
• Server-sent notifications
• Live sports scores or election results
• Progress updates for long-running tasks

⚠️ 𝗪𝗵𝗲𝗻 𝘁𝗼 𝗮𝘃𝗼𝗶𝗱

• If you need bidirectional communication (client sending frequent messages back)
• If you need Binary data (SSE is text-only)
• When you have very high-frequency updates (hundreds per second)
• If you need guaranteed delivery (SSE doesn't have acknowledgments)

🎯 𝗣𝗲𝗿𝗳𝗲𝗰𝘁 𝗳𝗼𝗿 𝗶𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄𝘀

Mention SSE when designing notification systems, real-time dashboards, or any "server pushes updates to many clients" scenario. Great middle ground between simple polling and complex WebSocket infrastructure.