EventTypes

EventTypes, or event types, are identifiers that categorize events in event-driven systems. An event type labels an occurrence to which components may subscribe, and helps decouple producers from consumers. The event type is usually distinct from the event payload, which carries the details of the occurrence.

In practice, event types appear as strings, symbols, or enumerations. Browser environments expose events with a type such as click or keydown; server frameworks and message buses register listeners by named keys or by a defined enum. A closed set supports validation and type safety.

Event types are typically paired with a payload that carries context such as identifiers, timestamps, or domain data. The separation of type and data enables flexible routing: listeners subscribe to a type and access the accompanying payload to perform logic.

Design considerations include naming clarity, versioning, and avoiding semantic drift between producers and consumers. Using stable names, deprecating old types gradually, and validating emitted types against a schema helps maintain compatibility in evolving systems.

Event types enable common patterns such as domain events, event streams, and publish-subscribe. They support decoupled architectures but require discipline to prevent proliferation of types and to ensure listeners interpret payloads consistently.

See also: event-driven architecture, event bus, event sourcing, listeners, payload.