angular-core

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());
}