RxJS Interop

Priority: P1 (HIGH)

Principles

• Async to Sync: Use toSignal(observable$, { initialValue: defaultValue }) from @angular/core/rxjs-interop to convert Observables (HTTP, Events) to Signals for template rendering. Call in an injection context (class field or constructor). toSignal auto-unsubscribes on component destroy. Provide initialValue to avoid undefined.
• Sync to Async: Use toObservable(this.query) when you need RxJS operators (debounceTime, switchMap, distinctUntilChanged) on a Signal. Then wrap back with toSignal() if rendering.
• Auto-Unsubscribe: toSignal automatically unsubscribes.
• Cleanup: Use takeUntilDestroyed() for manual subscriptions in injection contexts. For use outside, inject(DestroyRef) and call takeUntilDestroyed(destroyRef).

Guidelines

• HTTP Requests:
  • GET: http.get<User[]>(...).pipe(catchError(() => of([]))) -> toSignal(..., { initialValue: [] }). Use in templates as {{ users() }}.
  • Consider httpResource() for simpler reactive HTTP in newer versions.
  • POST/PUT: Trigger explicit subscribe() or lastValueFrom().
• Race Conditions: Handle async loading states. toSignal requires an initialValue or handles undefined.

Anti-Patterns

• No manual subscribe in templates: Use toSignal() for Observables rendered in templates.
• No BehaviorSubject for state: Replace with signal() + toObservable() for RxJS interop.
• No global takeUntil: Use takeUntilDestroyed() scoped to the injection context. Never use a global Subject with takeUntil — it leaks if Subject is never completed.

References

• Signals vs Observables