Signals & Fine-Grained Reactivity

Angular 20, released May 2025, stabilized Signals, enabling zoneless applications that save approximately 100KB of bundle weight and avoid costly zone.js change detection cycles. Concrete benchmarks show that a complex Angular form with 50 bindings builds 50 subscriptions with Observables, while a Signal-based approach rebuilds only computed expressions that read changed values. The State of React 2025 survey of 3,760 developers found that 37% report `useEffect` as problematic, highlighting signals' appeal for explicit dependency tracking. The TC39 signals proposal aims to standardize this primitive across Angular, Solid, Preact, and Vue, reducing fragmentation. In Solid.js, which has used this model since inception, DOM updates touch exactly the elements whose data changed—no virtual DOM diffing required. Signals are not a replacement for RxJS in async event-driven code but are a better primitive for synchronous derived UI state, and Angular's `toSignal()` / `toObservable()` bridge makes them complementary.