angular-signals

Create writable state with signal(initialValue), read it by calling the signal as a function, and update it with set() or update(). Derive dependent values with computed(), which automatically recalculates when its signal dependencies change.

Use toSignal() from @angular/core/rxjs-interop to convert an Observable or BehaviorSubject into a signal. Pass { requireSync: true } for BehaviorSubject since it emits synchronously, or provide an initialValue for observables that emit asynchronously.

computed() creates read-only derived state that recalculates from dependencies, while linkedSignal() creates writable state that resets when its source changes. Use linkedSignal when users can override a value that should re-initialize when upstream data changes.

Use effect() for side effects that must run when signals change, such as logging or syncing to external systems. Effects must run in an injection context, typically the constructor, and are automatically cleaned up when the component is destroyed.

Use the resource() API with a params function and an async loader. The resource automatically refetches when params change and exposes value, isLoading, error, and status signals, with support for abort signals and conditional loading.

Test signals by calling them as functions to read values and using set() or update() to change state, then assert on computed results directly. For services using HttpClient, combine TestBed with provideHttpClientTesting and HttpTestingController.