angular-core

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

// ✅ 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>();

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()));

// ❌ 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');

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

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

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

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

@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> }
}

// ✅ 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: [] });

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

npm uninstall zone.js