I want to explain why Angular Signals matter, without diving too deep into technical details. Let’s start by clarifying what reactivity means and why Signals are the first real primitive for Angular.

What Does “Reactive” Even Mean?

“Reactivity” is a heavily overloaded term in web development. Its meaning depends on the context. Let’s break it into two key types:

1. Reactivity at the JavaScript Runtime Level

This happens when data changes and observers are notified, purely within the JavaScript runtime. It’s about managing data and notifying subscribers, with no UI involved.

Examples:

  • RxJS Observables
  • SolidJS Signals
  • MobX Observables
  • Framework-neutral signals (e.g., @preact/signals)

Here, changes are immediate and predictable in JavaScript. But what about the UI?

2. Reactivity at the UI Level

This is about updating the DOM when data changes. The DOM is part of the browser, not JavaScript, so your framework needs to know when something changes to trigger rendering.

When we talk about Angular Signals being reactive, we mean they handle this UI-level reactivity—updating the view when data changes, without manual intervention.

What Does “Primitive” Mean?

A primitive is a built-in, fundamental capability, not something patched onto existing features or wrapped around third-party tools.

Why RxJS Is Not a Reactivity Primitive for Angular

Traditionally, Angular doesn’t require reactive data to achrieve UI reactivity. With Zone.js, Angular could intercept async operations (like Promises or user events) and automatically trigger change detection. Plain JavaScript objects worked fine because Angular’s change detection always runs top-down, checking every component.

But this has drawbacks:

  • Over-checking leads to unnecessary performance costs.
  • Developers need to manage OnPush strategies and pass data top-down to optimize rendering.
  • If data changes inside a component, you’re often stuck calling markForCheck() or relying on tricks.

RxJS is a 3rd-party, external library to Angular. It helps—especially with the AsyncPipe—but it’s still JavaScript-level reactivity, not UI-level. Angular must bridge the gap using change detection and async mechanisms.

RxJS wasn’t designed to integrate deeply with Angular’s rendering lifecycle. It’s powerful, but it’s not a primitive for Angular’s reactivity system.

Why Angular Signals Are a Reactivity Primitive for Angular

Signals solve these problems directly. They:

  • Provide JavaScript and UI reactivity in one.
  • Integrate natively with Angular’s rendering and change detection.
  • Require no additional plumbing (no AsyncPipe, no markForCheck()).

Key Features of Angular Signals:

  1. Seamless integration with Angular’s reactivity graph.
  2. Intelligent change detection scheduling—works with Zone.js or zoneless.
  3. Fine-grained reactivity, updating only affected components, not the entire app.
  4. A pull-based model—no subscriptions, no unsubscriptions.
  5. Consistent behavior in both Default and OnPush components.

With Signals, Angular moves beyond the limitations of Zone.js and traditional change detection. It’s reactivity designed specifically for Angular’s needs.

Conclusion

Angular Signals represent the next step in Angular’s evolution. They’re the first native, first-class reactivity primitive for Angular, eliminating the need for zones, hacks, or boilerplate.

Unlike RxJS or external signal libraries, Angular Signals are:

  • Built into Angular.
  • Integrated with its rendering engine.
  • Optimized for efficient and predictable updates.