Apa itu lifecycle hook komponen Angular?

Question

Accepted Answer

**Lifecycle hook** minangka metode sing dipanggil Angular ing padhang-padhang spesifik sajrone uripe komponen — paggawenan, owah-owahan input, rendering, lan karusakan. Sampeyan nglaksanaake kanthi nambah metode interface menyang kelas komponen sampeyan.

## Hook utama kanthi urutan

```ts
import { Component, OnInit, OnDestroy, OnChanges, SimpleChanges } from "@angular/core";

@Component({ ... })
export class MyComponent implements OnInit, OnDestroy, OnChanges {
  ngOnChanges(changes: SimpleChanges) {
    // called when an @Input value changes (before ngOnInit the first time)
  }
  ngOnInit() {
    // called ONCE after the first ngOnChanges — do initialization, fetch data
  }
  ngOnDestroy() {
    // called just before the component is removed — CLEAN UP here
  }
}
```

## Urutan lengkap

```text
constructor          → DI happens; inputs NOT yet available
ngOnChanges          → when @Input values are set/changed
ngOnInit             → once, after first ngOnChanges ★ (init, fetch data)
ngDoCheck            → every change detection run (custom change detection)
ngAfterContentInit   → projected content (<ng-content>) initialized
ngAfterViewInit      → the component's view + child views ready ★ (access @ViewChild)
ngAfterViewChecked   → after each view check
ngOnDestroy          → before removal ★ (unsubscribe, clear timers)
```

## Telu sing paling digunake

```ts
ngOnInit() {
  this.userService.getUsers().subscribe(u => this.users = u); // init/fetch — inputs are ready
}
ngAfterViewInit() {
  this.chart.nativeElement.focus(); // the DOM/@ViewChild exists now
}
ngOnDestroy() {
  this.subscription.unsubscribe();   // prevent memory leaks!
  clearInterval(this.timer);
}
```

- **`ngOnInit`** — papan standar kanggo inisialisasi lan pangambilan data (beda karo konstruktor, `@Input` kasedhiya ing kene).
- **`ngAfterViewInit`** — nalika view bocah lan referensi `@ViewChild` wujud.
- **`ngOnDestroy`** — pembersihan: unsubscribe saka Observable, resiki timer, hapus listener.

## Napa ngOnInit tinimbang konstruktor

Konstruktor kudu mung nindakake DI; input durung dikunci ing kana. `ngOnInit` lumampah sawise Angular wis nyiyapake komponen lan input-ipun — papan sing bener kanggo logika startup.

## Napa iku penting

Lifecycle hook ngidini sampeyan nindakake logika ing wektu sing tepat — inisialisasi ing `ngOnInit`, akses view sing dirender ing `ngAfterViewInit`, lan wigati **pembersihan ing `ngOnDestroy`** (unsubscribe saka Observable minangka cara nomer 1 kanggo nglindungi memory leak ing Angular).

Ngerti urutan lan peran saben hook penting kanggo pangambilan data sing bener, akses DOM, lan manajemen sumber daya.