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BehaviorSubject vs Signals in Angular

In modern Angular (v16+), developers now have two powerful reactive tools

  • BehaviorSubject from RxJS

  • Signals, introduced natively in Angular 16

Both manage state — but they are built for different problems.

This article explains:

  • The conceptual difference

  • A real-world example (E-commerce Cart)

  • Performance implications

  • A modern hybrid solution (best practice in 2026)

Conceptual Difference

BehaviorSubject

  • A BehaviorSubject is:

  • A special type of Observable

  • Requires an initial value

  • Emits the latest value to new subscribers

  • Push-based stream

  • Designed for async flows

It’s ideal for:

  • HTTP responses

  • WebSocket data

  • Complex async transformations

  • Event streams

Signal

A Signal is:

  • A reactive value container

  • Pull-based

  • No subscription needed

  • Automatically tracked by Angular

  • Fine-grained reactive updates

It’s ideal for:

  • UI state

  • Derived state

  • Component state

  • Performance-sensitive rendering

Real-Time Example: E-Commerce Cart

Let’s imagine:

  • User adds products to cart

  • Cart total updates instantly

  • Products are loaded from API

  • UI must update efficiently

Version 1: Using BehaviorSubject (Classic Angular)

cart.service.ts

@Injectable({ providedIn: 'root' })
export class CartService {

  private cartSubject = new BehaviorSubject<Product[]>([]);
  cart$ = this.cartSubject.asObservable();

  addToCart(product: Product) {
    const current = this.cartSubject.value;
    this.cartSubject.next([...current, product]);
  }

  getTotal(): number {
    return this.cartSubject.value.reduce((sum, p) => sum + p.price, 0);
  }
}

cart.component.ts

export class CartComponent implements OnInit, OnDestroy {

  cart: Product[] = [];
  total = 0;
  sub!: Subscription;

  constructor(private cartService: CartService) {}

  ngOnInit() {
    this.sub = this.cartService.cart$.subscribe(cart => {
      this.cart = cart;
      this.total = cart.reduce((s, p) => s + p.price, 0);
    });
  }

  ngOnDestroy() {
    this.sub.unsubscribe();
  }
}

Problems

  • Manuals subscribe/unsubscribe

  • Boilerplate

  • Whole component re-evaluates

  • Not fine-grained

  • Easy to create memory leaks

Version 2: Using Signals (Modern Angular)

cart.service.ts

@Injectable({ providedIn: 'root' })
export class CartService {

  cart = signal<Product[]>([]);

  total = computed(() =>
    this.cart().reduce((sum, p) => sum + p.price, 0)
  );

  addToCart(product: Product) {
    this.cart.update(items => [...items, product]);
  }
}

cart.component.ts

export class CartComponent {
  constructor(public cartService: CartService) {}
}

cart.component.html

<div *ngFor="let item of cartService.cart()">
  {{ item.name }} - {{ item.price }}
</div>

<h3>Total: {{ cartService.total() }}</h3>

Why Signals Win Here

  • No subscriptions

  • No memory leak risk

  • Computed total auto-updates

  • Only total re-renders when cart changes

  • Less code

  • Better performance

Performance Comparison

FeatureBehaviorSubjectSignal
Change detectionZone-basedFine-grained
Subscription overheadYesNo
Memory leaks riskYesNo
Rendering optimizationLimitedPrecise
BoilerplateHighLow

Important

BehaviorSubject triggers:

  • Emission → Subscription → Change detection

Signals trigger:

  • Dependency tracking → Only affected bindings re-render

This makes Signals significantly more efficient for UI state.

But Signals Are NOT a Replacement for RxJS

Now let’s extend our cart example.

Products come from API:

this.http.get<Product[]>('/api/products')

We may need:

  • switchMap

  • debounceTime

  • retry

  • catchError

Signals cannot replace RxJS operators.

This is where hybrid architecture shines.

Hybrid Solution (Modern Best Practice)

Use:

  • RxJS for async streams

  • Signals for UI state

Example Hybrid Cart Service

@Injectable({ providedIn: 'root' })
export class CartService {

  // RxJS for API stream
  private products$ = this.http.get<Product[]>('/api/products');

  // Convert observable to signal
  products = toSignal(this.products$, { initialValue: [] });

  // UI state as signal
  cart = signal<Product[]>([]);

  total = computed(() =>
    this.cart().reduce((sum, p) => sum + p.price, 0)
  );

  addToCart(product: Product) {
    this.cart.update(items => [...items, product]);
  }

  constructor(private http: HttpClient) {}
}

Now:

  • API → handled by RxJS

  • UI state → handled by Signals

  • Templates stay clean

  • No subscriptions anywhere

  • High performance

  • Fully reactive

When To Use Which

Use Signals When:

  • Managing component state

  • Building dashboards

  • Forms

  • Derived UI values

  • Performance-sensitive UI

  • Working zoneless

Use BehaviorSubject When:

  • Handling async event streams

  • WebSockets

  • Complex operator chains

  • Interacting with legacy RxJS code

  • Advanced reactive flows

Use Hybrid When:

  • Building real-world applications

  • Fetching data from APIs

  • Managing UI state

  • Scaling modern Angular apps

Final Takeaway

BehaviorSubject = Reactive stream tool

Signals = Reactive UI state tool

They solve different problems.

Modern Angular applications should:

  • Use RxJS for async

  • Use Signals for state

  • Bridge them with toSignal()

That gives you:

  • Cleaner code

  • Better performance

  • Easier maintenance

  • Future-proof architecture

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