angular-core

name	angular-core
description	Angular core patterns: standalone components, signals, inject, control flow, zoneless. Trigger: When creating Angular components, using signals, or setting up zoneless.
metadata	{"author":"gentleman-programming","version":"1.0"}

Standalone Components (REQUIRED)

Components are standalone by default. Do NOT set standalone: true.

@Component({
  selector: 'app-user',
  imports: [CommonModule],
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `...`
})
export class UserComponent {}

---

Input/Output Functions (REQUIRED)

// ✅ ALWAYS: Function-based
readonly user = input.required<User>();
readonly disabled = input(false);
readonly selected = output<User>();
readonly checked = model(false);  // Two-way binding

// ❌ NEVER: Decorators
@Input() user: User;
@Output() selected = new EventEmitter<User>();

---

Signals for State (REQUIRED)

readonly count = signal(0);
readonly doubled = computed(() => this.count() * 2);

// Update
this.count.set(5);
this.count.update(prev => prev + 1);

// Side effects
effect(() => localStorage.setItem('count', this.count().toString()));

---

NO Lifecycle Hooks (REQUIRED)

Signals replace lifecycle hooks. Do NOT use ngOnInit, ngOnChanges, ngOnDestroy.

// ❌ NEVER: Lifecycle hooks
ngOnInit() {
  this.loadUser();
}

ngOnChanges(changes: SimpleChanges) {
  if (changes['userId']) {
    this.loadUser();
  }
}

// ✅ ALWAYS: Signals + effect
readonly userId = input.required<string>();
readonly user = signal<User | null>(null);

private userEffect = effect(() => {
  // Runs automatically when userId() changes
  this.loadUser(this.userId());
});

// ✅ For derived data, use computed
readonly displayName = computed(() => this.user()?.name ?? 'Guest');

When to Use What

Need	Use
React to input changes	effect() watching the input signal
Derived/computed state	computed()
Side effects (API calls, localStorage)	effect()
Cleanup on destroy	DestroyRef + inject()

// Cleanup example
private readonly destroyRef = inject(DestroyRef);

constructor() {
  const subscription = someObservable$.subscribe();
  this.destroyRef.onDestroy(() => subscription.unsubscribe());
}

---

inject() Over Constructor (REQUIRED)

// ✅ ALWAYS
private readonly http = inject(HttpClient);

// ❌ NEVER
constructor(private http: HttpClient) {}

---

Native Control Flow (REQUIRED)

@if (loading()) {
  <spinner />
} @else {
  @for (item of items(); track item.id) {
    <item-card [data]="item" />
  } @empty {
    <p>No items</p>
  }
}

@switch (status()) {
  @case ('active') { <span>Active</span> }
  @default { <span>Unknown</span> }
}

---

RxJS - Only When Needed

Signals are the default. Use RxJS ONLY for complex async operations.

Use Signals	Use RxJS
Component state	Combining multiple streams
Derived values	Debounce/throttle
Simple async (single API call)	Race conditions
Input/Output	WebSockets, real-time
	Complex error retry logic

// ✅ Simple API call - use signals
readonly user = signal<User | null>(null);
readonly loading = signal(false);

async loadUser(id: string) {
  this.loading.set(true);
  this.user.set(await firstValueFrom(this.http.get<User>(`/api/users/${id}`)));
  this.loading.set(false);
}

// ✅ Complex stream - use RxJS
readonly searchResults$ = this.searchTerm$.pipe(
  debounceTime(300),
  distinctUntilChanged(),
  switchMap(term => this.http.get<Results>(`/api/search?q=${term}`))
);

// Convert to signal when needed in template
readonly searchResults = toSignal(this.searchResults$, { initialValue: [] });

---

Zoneless Angular (REQUIRED)

Angular is zoneless. Use provideZonelessChangeDetection().

bootstrapApplication(AppComponent, {
  providers: [provideZonelessChangeDetection()]
});

Remove ZoneJS:

npm uninstall zone.js

Remove from angular.json polyfills: zone.js and zone.js/testing.

Zoneless Requirements

• Use OnPush change detection
• Use signals for state (auto-notifies Angular)
• Use AsyncPipe for observables
• Use markForCheck() when needed

---

Resources

• https://angular.dev/guide/signals
• https://angular.dev/guide/templates/control-flow
• https://angular.dev/guide/zoneless