Understanding when Angular executes your code is vital for building bug-free applications. The lifecycle hooks provide visibility into the component's internal state.
1The Sequence of Events
A component's life starts with the constructor, followed immediately by ngOnChanges. Once inputs are settled, ngOnInit runs. After the view is composed, ngAfterViewInit fires. This sequence is deterministic. If you try to access a @ViewChild in ngOnInit, it will likely be undefined because the view hasn't been initialized yet. Mastering this order prevents the 'ExpressionChangedAfterItHasBeenCheckedError' and other common pitfalls.
2Strategic Cleanup
The ngOnDestroy hook is the most important for application health. In a single-page application, components are frequently created and destroyed as the user navigates. If you subscribe to a global stream or set a setInterval in a component, that work continues even after the component is gone unless you manually stop it in ngOnDestroy. This is the single biggest cause of memory leaks and performance degradation in large-scale Angular apps.
