Event
An event is an occurrence, change, or associated record or notification recognized as significant within a system or context.
Architecture Modernization: Socio-technical alignment of software, strategy, and structure
A domain event is a record or description of something significant that happened within a business domain, phrased in the past tense.
- How it is used
- Maps business activity on an EventStorming timeline and, in software, signals changes between bounded contexts and a legacy model.
- How deep it goes
- Defines past-tense events, develops timeline and granularity heuristics, and shows process-modeling syntax without detailing event implementation.
- Examples
- Uses “Review Added,” “Contract Approval Requested,” and “Job Published” to illustrate business timelines, workflows, and legacy integration.
- What you can do after
- Practice/perform event naming and timeline mapping, then evaluate where a system-produced event advances a workflow.
Web Components in Action
A change event is a browser-dispatched DOM event indicating that the value of a form control has changed.
- How it is used
- Uses a select control’s change event to update a custom element’s layout attribute.
- How deep it goes
- Defines native events as browser-generated and works through one change handler, without detailing change-event timing.
- Examples
- Shows a select menu choosing among business-card templates by passing event.target.value to setAttribute.
- What you can do after
- Apply it via DOM event handlers to update a custom element’s attribute from a select menu.
React Quickly, Second Edition
A change event is a browser event dispatched when the value of a form control changes.
- How it is used
- Connects user interactions and browser changes to React handlers that update an interface.
- How deep it goes
- Explains JSX listeners, React event objects, propagation, default actions, and when to attach listeners manually.
- Examples
- Uses a counter button, mouse-movement status, video playback controls, and link navigation.
- What you can do after
- Apply it via React JSX handlers to respond to supported events, or attach JavaScript listeners for targets outside React.
Software Design for Python Programmers
An event is an occurrence defined by an object's behavior that can cause the object to transition from one state to another.
- How it is used
- Models runtime occurrences that trigger object state changes and support notification among dependent objects.
- How deep it goes
- Defines events through UML transitions and Python examples, but stops short of formal event-system internals.
- Examples
- Uses Car movement, Student course enrollment, baseball hits, and a thread-synchronization signal as concrete event examples.
- What you can do after
- Evaluate object design by tracing events, behaviors, states, transitions, and dependent-object notifications.
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Kafka for Architects
An event is a recorded occurrence or state change that can notify other components about something that happened in a system.
- How it is used
- Signals state changes to independent subscribers instead of requiring direct service calls.
- How deep it goes
- Defines immutable, timestamped facts and works through granularity and contract decisions, without a low-level producer implementation.
- Examples
- Uses customer address notifications and alternative user-profile update structures to show subscribers and event granularity.
- What you can do after
- Evaluate/understand event boundaries and define a producer-consumer contract before mapping events to Kafka messages.
MongoDB 8.0 in Action, Third Edition
An event is a record or notification that represents something that has occurred in a system and may trigger processing by other components.
- How it is used
- Connects producers and consumers without repeated polling or direct service-to-service requests.
- How deep it goes
- Defines events through application scenarios, compares processing locations, and details change-event handling with triggers; event payload design is not specified.
- Examples
- Uses logins, thermostat adjustments, inventory updates, and MongoDB insert, update, and delete notifications.
- What you can do after
- Operate/configure event handling through Atlas Database Triggers by selecting watched operations, filtering change events, and choosing ordering behavior.
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Build a Frontend Web Framework (From Scratch)
An event is a notification that an action or occurrence has happened, optionally carrying additional information but not requesting an action itself.
- How it is used
- Maps browser notifications to TODO commands and enables child-to-parent component communication.
- How deep it goes
- Defines events against commands and describes custom-event handlers, dispatcher subscription, and unmount cleanup.
- Examples
- Traces TODO button clicks and Enter presses to one action, then contrasts React callbacks with Vue custom events.
- What you can do after
- Build it from scratch by wiring DOM listeners and a component dispatcher for child events heard by parents.
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Kubernetes in Action, Second Edition
A Kubernetes Event is an API object that records an occurrence or state transition involving a cluster object.
- How it is used
- Helps inspect recent controller activity and quickly identify problems affecting Kubernetes API objects.
- How deep it goes
- Explains event types, fields, lifecycle, retention, commands, and YAML limitations, but stops short of event creation internals.
- Examples
- Uses Node startup events and a Pod sequence covering scheduling, image pulling, container creation, and container startup.
- What you can do after
- Diagnose/debug with it by listing events, filtering Warnings, reading fields, and tracing an object’s recent lifecycle.
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Pro ASP.NET Core 7, Tenth Edition
An event is a browser or user-interface occurrence that can trigger application code, such as a click or form interaction.
- How it is used
- Connects browser interactions to Blazor Server component state and carries selection changes from child components to parents.
- How deep it goes
- Works through handler registration, event arguments, lambdas, browser-behavior controls, custom callbacks, and component bindings.
- Examples
- Uses clickable counters, a form button, nested click handlers, and a city selector that highlights table rows.
- What you can do after
- Build it from scratch with Blazor Server event handlers, child-to-parent EventCallback<T> notifications, and component bindings.
Pro Angular 16
A browser event is an object representing an occurrence that can provide information to event handlers about the occurrence and its source.
- How it is used
- Uses events to connect browser interactions and directive notifications to Angular template expressions.
- How deep it goes
- Defines shared Event properties and works through input handling and directive output without detailing browser event-dispatch internals.
- Examples
- Demonstrates product-name input, Enter-key filtering, and a table-row click that sends a product category to a form.
- What you can do after
- Apply it via Angular event bindings and EventEmitter to read input with a type guard and pass values from directives.
Akka in Action, Second Edition
An event is a stored record of a state-changing outcome generated by a persistent actor after processing a command.
- How it is used
- Decouples actors and external notifications through publish-subscribe messages, while recording accepted persistent-actor changes for recovery.
- How deep it goes
- Defines events, traces command validation through journal storage and replay, and outlines typed handlers without fully detailing their implementation.
- Examples
- Uses conversation message publication, mentions notifications, browser delivery, and a cargo container with AddCargo and CargoAdded.
- What you can do after
- Apply it via Akka Persistence to model accepted commands as stored events and recover state by replaying a journal.
Secrets of the JavaScript Ninja, Second Edition
A detectable occurrence, such as a user action or timer firing, to which a program can respond.
- How it is used
- Coordinates browser application behavior by triggering handler execution in response to user, network, or timer occurrences.
- How deep it goes
- Explains queued, one-at-a-time handler execution, while deferring detailed event-loop effects to later treatment.
- Examples
- Uses clicks, mouse moves, keyboard presses, timers, and network or Ajax events as examples.
- What you can do after
- Understand how browser events queue for handlers and why long-running handlers can make applications unresponsive.
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Apache Kafka in Action
An event is a record representing a significant occurrence, change, activity, transaction, or incident and its associated information.
- How it is used
- Connects enterprise systems by publishing business occurrences for asynchronous consumption and processing.
- How deep it goes
- Defines events, distinguishes them from message types, and explains self-contained sizing without detailing event schemas or processing code.
- Examples
- Uses user interactions, system updates, financial transactions, uploaded PDFs, and semantically split SOAP messages as examples.
- What you can do after
- Apply event modeling by publishing self-contained business occurrences to Kafka and notifying consumers about externally stored files.
Logs and Telemetry
An event is a discrete record representing an occurrence or data item processed by a telemetry system.
- How it is used
- Uses events as the basic units for ingesting, routing, processing, and delivering telemetry through Fluent Bit.
- How deep it goes
- Defines metadata, timestamps, and records, then explains routing and payload forms without detailing complete plugin implementations.
- Examples
- Uses log, metric, trace, container, application, and Kubernetes telemetry as event examples.
- What you can do after
- Apply it via Fluent Bit plugins to route events with tags and access or manipulate their records.
Effective Platform Engineering
An event is a lightweight record indicating that something occurred, optionally including the location and whether the occurrence passed or failed.
- How it is used
- Uses lightweight events to decouple platform changes from consumers that automate releases, issue tracking, observability, and auditing.
- How deep it goes
- Defines event shape and demonstrates several consumers, but stops short of specifying schemas, delivery guarantees, or consumer implementation details.
- Examples
- Shows Kubernetes pod termination, successful deployment, Istio rollout, dependency update, deprecation, and deployment-correlation events.
- What you can do after
- Apply it via event consumers to automate coordination, improve operational traceability, and connect changes with their downstream effects.
Troubleshooting Java, Second Edition
An event is a message representing something that has already happened in a system.
- How it is used
- Uses events to communicate between services and investigate missing, delayed, or incorrectly processed messages.
- How deep it goes
- Defines events, messages, brokers, logs, and replay, then stops short of implementation details for producing or consuming events.
- Examples
- Uses UserRegistered, PaymentProcessed, and InventoryReserved events plus a missing welcome-email investigation.
- What you can do after
- Diagnose missing or out-of-order behavior by examining event logs and replaying recorded messages in test environments.
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Cloud Observability in Action
An event is an occurrence of interest in code, including expected behavior and unexpected or erroneous behavior.
- How it is used
- Frames occurrences in code as signals that can be logged, correlated, and captured through instrumentation.
- How deep it goes
- Defines events, distinguishes expected and erroneous behavior, and connects them to logging and instrumentation without detailing event schemas.
- Examples
- Uses completed uploads, failed shopping-basket writes, debug events, and production INFO, WARNING, or ERROR events.
- What you can do after
- Apply event concepts by structuring useful logs and adding manual OpenTelemetry signals where automatic instrumentation lacks business context.
Kafka Streams in Action, Second Edition
An event is a record of something that happened, especially business-critical data whose preservation has lasting significance.
- How it is used
- Frames purchases, clicks, and sensor transmissions as records that feed continuous event streams.
- How deep it goes
- Defines events through keys, values, and timestamps, then distinguishes durable business records from ephemeral messages.
- Examples
- Uses purchases, link clicks, sensor transmissions, and a flux capacitor shipment with custody scans as examples.
- What you can do after
- Understand event streams by identifying each event’s key, payload, timestamp, and business significance.
Read how Kafka Streams in Action, Second Edition explains event →
Related concepts
- commandcontrasts with · A command is an instruction or request representing an operation for a system or component to interpret, handle, or execute.
- pivotal eventincludes · A pivotal event is a significant domain event that marks a transition between areas of an EventStorming timeline.
- software design EventStormingused by · Software design EventStorming is a collaborative modeling technique that explores domain events and processes to inform software structure and behavior.
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