An event is a signal that something has happened within a system, such as a user action, system update, or external trigger. Events can originate from frontend interactions, backend processes, or infrastructure-level activities. Applications often emit events to notify components that a change has occurred, allowing other parts of the system to react asynchronously. Events are widely used in UI programming, distributed systems, and event-driven architecture.
Why it matters
Events enable loose coupling between components. Instead of polling or synchronously requesting updates, systems can subscribe to events and respond only when necessary. This improves scalability, reduces resource usage, and simplifies the flow of information between distributed services.
Examples
A button click in the browser creates a DOM event. A backend may emit an event when a new order is created, which triggers downstream processes like sending confirmation emails. Lessons such as Event-Driven Systems explore these ideas in detail.