WebSockets for Builders
Learn to build real-time features with WebSockets, Socket.io, Server-Sent Events, and Pusher. From a first WebSocket server to authenticated rooms, presence indicators, and scaling across multiple processes.
What you'll learn
Course outline
Free — start now
Full course — $49 one-time
Broadcasting, Rooms, and Namespaces
Sending to specific users and organising channels
Presence and Online Indicators
Track who is online and broadcast connection state
Server-Sent Events
One-way real-time streaming without WebSocket overhead
Pusher — Serverless Real-Time
Real-time without managing a WebSocket server
Authenticating WebSocket Connections
JWT verification and session-based auth in Socket.io
Scaling WebSockets
Redis adapter, sticky sessions, and horizontal scaling
Get the full course
All 9 lessons. Build real-time features that users notice — chat, presence, and live updates.
Written by the RadarTrek editorial team · Reviewed June 2026
About this course
WebSockets solve a problem that HTTP cannot: keeping a persistent, bidirectional connection open between a client and server so that either side can send data at any time. The standard HTTP request-response cycle requires the browser to ask and the server to answer — if new data arrives on the server after the response has been sent, there is no mechanism to push it to the client without the client asking again. For a chat application, live collaborative document, real-time dashboard, or multiplayer game, that limitation is fatal. WebSockets replace the pull model with a push model: the connection opens once, stays open, and data flows in both directions as events occur.
In the Node.js and Next.js ecosystem, Socket.io is the dominant library for WebSockets — it handles connection fallbacks, room management, and reconnection automatically. For serverless environments like Vercel that cannot maintain persistent TCP connections, Pusher and Ably offer managed WebSocket infrastructure via a REST API. For simpler one-way streaming (server pushing updates to browser), Server-Sent Events provide a lighter-weight alternative that works over standard HTTP. This course covers all three patterns and teaches you to choose the right tool for your use case.
Frequently asked questions
What is a WebSocket and how is it different from HTTP?
HTTP is a request-response protocol: the browser sends a request and the server sends one response, then the connection closes. WebSockets are a persistent, full-duplex protocol: after an initial HTTP handshake upgrades the connection, both sides can send messages at any time without re-establishing the connection. This makes WebSockets ideal for any use case where the server needs to push updates to the client — chat, live notifications, real-time dashboards, collaborative editing, and multiplayer features.
What is Socket.io and do I need it, or can I use raw WebSockets?
The browser natively supports WebSockets via the WebSocket API, but raw WebSockets require you to implement reconnection logic, event namespacing, room management, and fallback for environments where WebSockets are blocked. Socket.io adds all of these on top of WebSockets, falling back to long polling when WebSockets are unavailable. For production applications, Socket.io saves significant implementation time. For simple use cases or environments with WebSocket support guaranteed, raw WebSockets are also a valid choice.
Can I use WebSockets in Next.js on Vercel?
Standard WebSockets require persistent server processes, which are incompatible with Vercel's serverless function model. There are three solutions: run a separate Node.js WebSocket server (on Railway, Render, or a VPS) alongside your Vercel Next.js deployment; use Pusher or Ably, which are managed WebSocket services that work with serverless via a REST API; or use Server-Sent Events, which work over standard HTTP responses and are compatible with Vercel Edge Functions. This course covers all three approaches.
What are Server-Sent Events and when should I use them instead of WebSockets?
Server-Sent Events (SSE) are a browser API for receiving a stream of events from a server over a long-lived HTTP connection. Unlike WebSockets, SSE is one-directional — the server pushes, the client listens. This makes SSE simpler to implement and compatible with standard HTTP infrastructure (no WebSocket upgrade required). If your use case is server-to-client only — notifications, live feed updates, real-time logs — SSE is often the better choice. If you need the client to send data back on the same connection (chat, collaborative editing), use WebSockets.
How do I handle authentication in WebSocket connections?
WebSocket connections cannot send custom HTTP headers during the initial handshake, which means the standard Authorization: Bearer header approach does not work. The two common solutions are: pass the JWT as a query parameter in the WebSocket URL (simpler but exposes the token in logs), or perform a separate HTTP authentication endpoint first and use a short-lived connection token for the WebSocket handshake. Socket.io also supports passing auth data in the connection payload via socket.auth, which is the recommended approach for Socket.io applications.