Angular Signals explained: How pull-based reactivity changes how we model state

Angular Signals are a pull-based reactivity primitive that model current state and explicit dependencies, rather than event sequences. Unlike RxJS observables, Signals don't broadcast events — they mark dependent computations as stale and recompute them on next read. This makes them ideal for state-heavy problems like form modeling, where validity, errors, and UI flags can be derived declaratively from a single source of truth. The Angular Signal Forms API formalizes this by wrapping a plain data model in a writable signal, attaching validation schemas via a form() function, and exposing field state (invalid, errors, pending) as derived signals — eliminating the need for subscriptions, lifecycle hooks, or imperative state toggling. RxJS remains the right tool for async workflows and external event coordination, while Signals excel at state derivation.