Signals vs. BehaviorSubjects in Angular:Why Signals Are the Superior Choice

Angular has been a powerful framework for building web applications, offering a wide array of tools and paradigms to facilitate reactive programming. With the recent introduction of Signals, Angular now provides a new way to manage reactive data flow, offering an alternative to RxJS, which has been the go-to solution for this purpose for years. But why would Angular introduce Signals when RxJS is already deeply integrated into the framework? Is there a real need for another reactive tool?

This blog post aims to explore these questions by comparing Signals with RxJS’s BehaviorSubjects, showing why Signals are often the better choice for managing reactive data in Angular.

The Problem with RxJS Complexity

RxJS is incredibly powerful, offering a wide variety of operators that allow for complex data flow management. However, this power comes with a significant learning curve. Concepts such as hot and cold observables, subscription management, and the proper use of operators like map, switchMap, and mergeMap can be overwhelming for beginners. Even seasoned developers can find themselves tangled in complex streams and memory leak issues if not careful.

In contrast, Signals aim to simplify reactive programming in Angular. They provide a more intuitive and less error-prone way to manage state and reactivity, especially for developers who are not already familiar with the intricacies of RxJS.

Signals vs. BehaviorSubjects: A Basic Comparison

Let’s start with a simple example to illustrate the differences between Signals and BehaviorSubjects.

// Angular Signal
data = signal(0);

// RxJS BehaviorSubject
data = new BehaviorSubject(0);

At first glance, the syntax for creating a Signal and a BehaviorSubject is quite similar. However, the differences become more apparent when you need to access these values in your Angular templates.

<!-- Using Angular Signal -->
{{ data() }}

<!-- Using RxJS BehaviorSubject with async pipe -->
{{ data | async }}

Here, Signals are accessed by calling them as a function, whereas BehaviorSubjects can be accessed using the async pipe. While the async pipe is a familiar concept to Angular developers, it introduces additional complexity, such as the need to manage subscriptions and the potential for memory leaks.

Accessing Values Directly

One of the key advantages of Signals is their simplicity when it comes to accessing values directly in your code. Consider the following example:

// Accessing Signal value
getData() {
  console.log(this.data()); // Outputs the current value of data
}

// Accessing BehaviorSubject value
getData() {
  console.log(this.data.value); // Outputs the current value of data
}

While both approaches are straightforward, the simplicity of Signals becomes even more apparent when dealing with derived values.

Derived Values: A Significant Difference

Derived values are values computed from other reactive data sources. Let’s see how this works with both Signals and BehaviorSubjects.

// Angular Signal
data = signal(0);
myData = computed(() => this.data() * 10);

// RxJS BehaviorSubject
data = new BehaviorSubject(0);
myData = this.data.pipe(map((data) => data * 10));

Again, the syntax is somewhat similar, but the key difference lies in how these derived values are handled.

Accessing Derived Values

With Signals, accessing the value of a computed property is as simple as calling the function:

myFunction() {
  console.log(this.myData()); // Outputs the computed value
}

With RxJS, however, you need to subscribe to the observable to access the derived value:

myFunction() {
  this.myData.subscribe((val) => console.log(val));
}

This introduces the need for managing subscriptions, which can lead to memory leaks if not handled correctly. In larger applications, the complexity of managing multiple subscriptions can quickly become a significant overhead.

Subscription Management and Memory Leaks

One of the most common pitfalls when working with RxJS is failing to properly manage subscriptions. Unsubscribed observables can lead to memory leaks, which can degrade the performance of your application over time. Here’s how you might handle this in a typical Angular component:

destroy$ = new Subject<void>();

ngOnDestroy() {
  this.destroy$.next();
  this.destroy$.complete();
}

someFunction() {
  this.myData.pipe(takeUntil(this.destroy$)).subscribe((val) => console.log(val));
}

In contrast, Signals eliminate the need for such manual subscription management, making your code cleaner and less error-prone.

Predictability and Order of Execution

Another significant advantage of Signals is their predictability. Signals always emit values in the order they are defined, making it easier to reason about your code and avoid unexpected behavior. This is not always the case with RxJS, where the order of emission can be influenced by factors like the type of observable and the operators used.

Consider the following example:

// Angular Signals
firstData = signal(5);
secondData = signal(10);

derivedData = computed(() => this.firstData() * this.secondData());

changeValues() {
  this.firstData.set(7);
  this.secondData.set(12);
}

Here, derivedData will always reflect the product of firstData and secondData, and the order of operations is guaranteed. With RxJS, achieving the same predictability requires more careful management:

// RxJS BehaviorSubjects
firstData = new BehaviorSubject(5);
secondData = new BehaviorSubject(10);

derivedData = combineLatest([this.firstData, this.secondData]).pipe(
  map(([one, two]) => one * two)
);

changeValues() {
  this.firstData.next(7);
  this.secondData.next(12);
}

Composition and Modularity

Signals offer another advantage over BehaviorSubjects in terms of their ease of composition. Signals can be easily composed by using other signals as input and producing a new signal as output. This functional approach promotes modularity and simplifies reasoning about your code.

// Composing Signals
firstData = signal(5);
secondData = signal(10);

composedSignal = computed(() => this.firstData() + this.secondData());

incrementFirstData() {
  this.firstData.set(this.firstData() + 1);
}

With RxJS, composition typically involves operators like mergeMap or switchMap, which can be more challenging to understand and maintain.

// Composing BehaviorSubjects
firstData = new BehaviorSubject(5);
secondData = new BehaviorSubject(10);

composedData = combineLatest([this.firstData, this.secondData]).pipe(
  map(([one, two]) => one + two)
);

incrementFirstData() {
  this.firstData.next(this.firstData.value + 1);
}

While RxJS offers more flexibility and power for complex data flows, Signals are often the better choice for simpler, more straightforward applications.

Performance Considerations

Because Signals are just functions, they can be optimized more easily by the Angular compiler, leading to faster and more efficient code. This is particularly important in performance-critical applications where every millisecond counts.

Moreover, the simpler mental model of Signals makes it easier to write and maintain performant code, as there is less risk of introducing inefficiencies through misconfigured observables or poorly managed subscriptions.

When to Use Signals vs. BehaviorSubjects

While Signals offer many advantages, they are not a complete replacement for RxJS. There are scenarios where RxJS’s power and flexibility are necessary, particularly in more complex applications that require advanced reactive programming techniques.

For instance, if your application requires complex data streams, real-time updates, or intricate event handling, RxJS remains the tool of choice. However, for simpler applications or components where you need a straightforward way to manage reactive data, Signals are often the superior choice.

Conclusion

Signals represent a significant step forward in Angular’s approach to reactive programming. By offering a simpler, more intuitive alternative to RxJS’s BehaviorSubjects, Signals make it easier to manage state and data flow in your Angular applications. They reduce the need for complex subscription management, eliminate the risk of memory leaks, and provide a more predictable and composable way to handle reactive data.

While RxJS will continue to be an essential tool for many Angular developers, Signals provide a welcome alternative that can simplify your code and improve your application’s performance. As Angular continues to evolve, Signals are likely to become an increasingly important part of the framework, offering a new way to build reactive applications with less complexity and more clarity.

Whether you are a seasoned Angular developer or just starting out, understanding the advantages of Signals over BehaviorSubjects will help you make more informed decisions about how to structure your reactive code.