What are Angular Signals?

Signals are a reactivity primitive introduced in Angular to make state management more declarative, efficient, and explicit. They provide a new way to handle and react to changes in data, much like observables but with synchronous and fine-grained reactivity, ideal for template-driven UIs.

Introduced in Angular 16, Signals aim to replace some use-cases of RxJS (like BehaviorSubject) in component state management by providing a simpler and zone-less reactivity model.

Conceptual Understanding

A value is held inside a container that is referred to as a Signal:

• Tracks its dependencies automatically when read.
• Notifies consumers when it is updated.
• Can be used directly in templates and logic without subscriptions or manual unsubscriptions.

Analogy

A signal behaves how a reactive variable does:

• Reading it establishes a dependency.
• Updating it notifies everything that depends on it.

Types of Signals in Angular

Angular provides three primary ways to work with signals:

Signal API Overview

Writable Signal — signal()

import { signal } from '@angular/core';
const count = signal(0); // Creates a signal with initial value 0
count(); // GET: returns 0
count.set(10); // SET: changes value to 10
count.update(v => v + 1); // Increments count

Computed Signal — computed()

import { computed } from '@angular/core';
const count = signal(2);
const double = computed(() => count() * 2);
console.log(double()); // 4
count.set(5);
console.log(double()); // 10 (automatically recalculates)

• Automatically recalculates when dependencies change.
• Pure function, no side-effects allowed inside.

Effect — effect()

import { effect } from '@angular/core';
const count = signal(0);
effect(() => { console.log(`Count changed to: ${count()}`);
});
count.set(5); // Automatically triggers the effect

• Use for side-effects: console logs, HTTP calls, DOM manipulation, etc.
• Automatically runs when dependent signal changes.

Real-life Example: Counter Component with Signals

import { Component, signal, computed, effect } from '@angular/core';
@Component({ selector: 'app-counter', template: ` <h2>Count: {{ count() }}</h2> <h3>Double: {{ doubleCount() }}</h3> <button (click)="increment()">Increment</button> `
})
export class CounterComponent { count = signal(0); // Writable signal doubleCount = computed(() => this.count() * 2); // Derived signal constructor() { effect(() => { console.log('Count updated to:', this.count()); }); } increment() { this.count.update(c => c + 1); }
}

Key Benefits of Signals

Signals vs Observables (RxJS)

Use Cases

• Local component state (counter, toggles, forms)
• Derived data in templates
• ViewModel composition
• Replacing BehaviorSubject in components

Angular Signal Lifecycle & Change Detection

• Signals track where they’re used.
• Change detection is triggered only where needed (fine-grained).
• This allows zone-less rendering and better performance.

Conclusion

Angular Signals offer a simpler, more efficient way to manage UI state with fine-grained reactivity and no need for zones. With built-in dependency tracking and a clean API, they streamline component logic and performance. To leverage these cutting-edge features, it’s wise to hire Angular developer experts familiar with Signals and modern Angular best practices.