Realtime web applications with ExpressJS and SocketIO

This document discusses building real-time web applications using ExpressJS and SocketIO. SocketIO allows for bidirectional communication between client and server through websockets. It handles establishing the websocket connection and provides events for sending and receiving data. This enables the server to push updates to clients in real-time without the client repeatedly requesting information. An example given is building a plane status board that updates automatically every time a flight's status changes, rather than requiring the client to check status every second. Key features covered include sending/receiving events, storing client data, namespaces, acknowledgements, broadcasting, and supporting mobile devices.