onDestroy

OnDestroy is a lifecycle hook in Angular that provides a hook for cleanup logic when a component, directive, or service instance is destroyed. It is implemented through the ngOnDestroy method and is part of the OnDestroy interface. Angular calls this method just before the instance is removed from the application, such as when a component is navigated away from or a directive is torn down.

To use it, a class declares that it implements OnDestroy and defines a ngOnDestroy(): void method. The framework invokes ngOnDestroy as part of its destruction sequence, after other lifecycle hooks have run and just before the element is removed from the DOM.

Common tasks in ngOnDestroy include unsubscribing from Observables, detaching event listeners, clearing timers, and releasing resources that were allocated during the component’s lifetime. Proper cleanup helps prevent memory leaks and ensures predictable shutdown of long‑running processes.

Example: class MyComponent implements OnDestroy { private sub: Subscription; ngOnInit() { this.sub = this.service.getData().subscribe(...); } ngOnDestroy() { this.sub?.unsubscribe(); } }

Notes: OnDestroy is typically used with components and directives. In Angular applications, providers created in a component injector may also be destroyed with the component, enabling cleanup of services tied to that component. It is not a language destructor.