Migrate To Signals

Migrate to Signals Skill

Convert legacy Angular patterns to modern signal-based APIs.

Input/Output Decorators → Signal Functions

Before

@Input() name: string = '';
@Input() count!: number;
@Output() clicked = new EventEmitter<void>();

After

readonly name = input<string>('');
readonly count = input.required<number>();
readonly clicked = output<void>();

Key Changes

• input() for optional inputs with defaults
• input.required<T>() for required inputs
• output<T>() replaces EventEmitter
• Add readonly modifier
• Import from @angular/core: input, output

ViewChild/ContentChild → Signal Queries

Before

@ViewChild('myRef') myRef!: ElementRef;
@ViewChild(ChildComponent) child!: ChildComponent;

After

readonly myRef = viewChild<ElementRef>('myRef');
readonly child = viewChild(ChildComponent);
// Access: this.myRef()?.nativeElement

BehaviorSubject → signal()

Before

private items$ = new BehaviorSubject<Item[]>([]);
items = this.items$.asObservable();

addItem(item: Item) {
  this.items$.next([...this.items$.value, item]);
}

After

readonly items = signal<Item[]>([]);

addItem(item: Item) {
  this.items.update(current => [...current, item]);
}

Observable Derived State → computed()

Before

totalCount$ = this.items$.pipe(map((items) => items.length));

After

readonly totalCount = computed(() => this.items().length);

Subscriptions → effect()

Before

ngOnInit() {
  this.items$.subscribe(items => {
    console.log('Items changed:', items);
  });
}

After

constructor() {
  effect(() => {
    console.log('Items changed:', this.items());
  });
}

Observable to Signal (interop)

import { toSignal } from '@angular/core/rxjs-interop';

// Convert observable to signal
readonly data = toSignal(this.http.get<Data[]>('/api/data'), { initialValue: [] });

Template Changes

Before

<div *ngIf="loading">Loading...</div>
<div *ngFor="let item of items$ | async">{{ item.name }}</div>

After

@if (loading()) {
<div>Loading...</div>
} @for (item of items(); track item.id) {
<div>{{ item.name }}</div>
}

Testing Signal Inputs

// Set input values in tests
fixture.componentRef.setInput('count', 5);
fixture.detectChanges();

Checklist

1. Replace @Input() → input() or input.required()
2. Replace @Output() → output()
3. Replace @ViewChild() → viewChild()
4. Replace BehaviorSubject → signal()
5. Replace derived observables → computed()
6. Replace subscriptions for side effects → effect()
7. Update templates: *ngIf → @if, *ngFor → @for
8. Remove | async pipes (signals auto-unwrap)
9. Run tests: npm test