Previously the go-to tool for reactivity has been RxJS and observables. With Angular 17 a new reactive building block has been introduced: signals. With this change Angular is shifting towards signal-based APIs and patterns. But as of 2025 this is still “work in progress” and there are dos and don’ts to consider:
HttpClient API for now, since with signals a pattern still has to emerge.computeds, no value$.pipe(take(1)).subscribe(value => ...)) and it is easy to define derived values with computed(() => ...).toSignal, but there are important things to note:
toSignal is not lazy, it subscribes to the observable (and causes the fetching of the data) no matter if the signal is read or not. The behavior can be compared to a “hot” observable.toLazySignal that only subscribes to the observable, when the signal is read.toSignal and toLazySignal only unsubscribe when the injector is destroyed (i.e. the component is destroyed), they won’t unsubscribe if the component stops using the signal due to a condition (@if) in the template.{ providedIn: "root" } should not use toSignal and toLazySignal, since these observables will never get unsubscribed, unless a “hot” observable is the desired behavior.toLazySignal when data fetching is involved.toLazySignal back with toObservable will cause them to be not lazy anymore.input and model signals are preferred over @Input since they allow to integrate in the reactive world nicely (no more Subject that is nexted in ngOnChanges). And also, they allow to mark inputs as input.required.output is preferred over @Output.