What are Angular Signals?

Let’s break down the differences between Angular Signals and Observables in depth, and provide examples so you get both the conceptual clarity and practical understanding.

Overview: Signals vs Observables

Conceptual Differences between Signals and Observables

Signals – Pull-based (Synchronous)

A Signal is like a reactive variable. You read from it like a function and Angular tracks all reads and automatically re-runs the dependent computations when values change.

Think of it like Excel: when a cell (signal) changes, all dependent cells update automatically.

Observables – Push-based (Asynchronous)

An Observable is an object that can stream various data or events that can be observed over time. You subscribe to it and it emits data (can be async). Great for event streams, API responses, user interactions, etc.

Think of it like a news subscription: you get notified (pushed) when something happens.

Basic Example

Using Signals

import { signal, computed, effect } from '@angular/core';
const count = signal(0);
const doubleCount = computed(() => count() * 2);
// Automatically re-runs when count changes
effect(() => { console.log('Double Count:', doubleCount());
});

Change signal

count.set(2); // console: Double Count: 4
count.update(n => n + 3); // console: Double Count: 10

• signal() creates reactive state
• computed() derives values
• effect() tracks dependencies and re-runs when needed

Using Observables

import { of } from 'rxjs';
import { map } from 'rxjs/operators';
const count$ = of(2); // Observable emitting 2
const doubleCount$ = count$.pipe( map(count => count * 2)
);
doubleCount$.subscribe(value => { console.log('Double Count:', value); // Output: 4
});

Key Observations:

• Observables use async operations by default (even if you use of)
• You pipe operations and subscribe to get values

Real-world Angular Usage

With Signals (State Management)

@Component({ standalone: true, template: ` <button (click)="increment()">Increment</button> <p>Count: {{ count() }}</p> `
})
export class CounterComponent { count = signal(0); increment() { this.count.update(c => c + 1); }
}

• No async pipe needed
• Just use count() to access

With Observables (Async data)

@Component({ template: ` <ul> <li *ngFor="let user of users$ | async">{{ user.name }}</li> </ul> `
})
export class UserComponent { users$: Observable<User[]>; constructor(private http: HttpClient) { this.users$ = this.http.get<User[]>('/api/users'); }
}

Key Takeaways:

• Perfect for asynchronous data like HTTP
• Requires | async pipe

Summary Table

When to Use What?

Interop Example: Convert Observable to Signal

import { toSignal } from '@angular/core/rxjs-interop';
constructor(http: HttpClient) { this.userSignal = toSignal(http.get<User>('/api/user'));
}

• Use toSignal() to connect async Observable to Signal

Conclusion

• Use Signals for synchronous state & reactivity inside Angular templates and components.
• Use Observables for asynchronous operations and stream-based data handling.
• They can co-exist and even convert between each other when needed.