fromEventTarget

FromEventTarget is a creation operator used in reactive programming with RxJS that creates an observable sequence from an EventTarget, such as a DOM element, window, or document. The resulting observable emits events whenever the specified event type(s) occur on the target.

The operator works by attaching a corresponding event listener to the target via addEventListener when a subscriber subscribes. Each time the event fires, the event object (or a transformed value, if a selector function is provided) is emitted to observers. When the subscription is disposed, the operator removes the event listener through removeEventListener, ensuring proper teardown and preventing memory leaks. If multiple event types are provided, the observable emits events from any of the specified types.

Parameters typically include the target and the event type(s). An optional selector or result projection function can be supplied to transform the event before emission. In addition, options for addEventListener, such as useCapture or { passive: true }, can be provided to influence listener behavior. If the eventName is an array of strings, the observable listens to all listed events on the same target.

Common use cases involve reacting to user interactions (clicks, key presses), window or element resizing, or other DOM events in a reactive programming style. It is a specialized variant of the more general fromEvent, tailored for standard EventTarget interfaces.

Limitations include that fromEventTarget works with objects implementing the EventTarget interface. It is not suitable for Node-style EventEmitter without adapters or wrappers. As with other RxJS creation operators, best practice includes proper teardown by unsubscribing to avoid memory leaks.

See also: fromEvent, fromEventPattern, addEventListener, removeEventListener.