EventTarget

EventTarget is an interface defined by the Web Platform that represents any object to which event listeners can be attached and from which events can be dispatched. It is a foundational element of the DOM event system. In browsers, many core objects implement EventTarget, including Window, Document, and Element instances, as well as several API-specific objects.

The interface provides three primary methods: addEventListener, removeEventListener, and dispatchEvent. addEventListener registers a listener for a given event type; the listener can be a function or an object with a handleEvent method. removeEventListener unregisters a previously registered listener. dispatchEvent dispatches an Event to the target, triggering listeners whose types match the event.

Listeners can be registered with either a boolean capture flag or an options object. The options may include capture, once, passive, and signal. The once option removes the listener after its first invocation. The passive option indicates that the listener will not call preventDefault, enabling optimization by the browser. The signal option attaches an AbortSignal to the listener, allowing automatic removal when the signal is aborted.

Events flow through a target in three phases: capture, target, and bubble. During capturing, events travel from the top-level ancestors down to the target; if propagation is not stopped, the event then reaches the target and may bubble up to ancestors. The event object contains information such as type, target, currentTarget, eventPhase, bubbles, cancelable, and defaultPrevented.

In practice, EventTarget provides a unified mechanism for event registration and dispatch across environments, supporting decoupled communication between event producers and consumers.