How does Socket.io work with the MERN stack?

Socket.io runs on the Node.js server alongside the Express.js API, sharing the same process. The same Express JWT middleware authenticates Socket.io connections, so security is consistent. Events emitted on the server broadcast to clients in specific rooms. TypeScript interfaces define event payloads shared between the Node.js emitter and the React handler, so mismatches are caught at compile time, not runtime.