Enhancing Side Effects in Angular with NgRx's signalMethod

NgRx has always been a trusted library for managing state in Angular applications. With the introduction of its Signals API, developers now have a more streamlined way to handle state changes and side effects. To handle those side effects the NgRx team recently introduced the signalMethod that simplifies reactive workflows and makes them more intuitive.

In this article, I’ll dive into the signalMethod, showcasing how it works through practical examples and why it’s an excellent addition to your Angular toolkit.

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What is signalMethod?

The signalMethod is a utility introduced by NgRx that allows you to manage side effects in a clean, reactive way. Unlike traditional approaches that may rely on RxJS operators or manual effect management, signalMethod lets you focus on what matters: the logic for handling changes.

It achieves this by combining signals with a processor function. This function reacts to changes in its input, whether it's a static value or a reactive signal. The result is a flexible yet powerful way to handle state-driven actions.

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Setting Up a Signal-Driven Action

Let’s start with a simple example: logging a message whenever a number doubles. Here’s how you can achieve this using signalMethod:

import { Component } from '@angular/core';
import { signalMethod } from '@ngrx/signals';

@Component({
  selector: 'app-math-logger',
  template: `<button (click)="increment()">Increment</button>`
})
export class MathLoggerComponent {
  private counter = signal(1);

  // Define the signal method
  readonly logDoubledValue = signalMethod<number>((value) => {
    const doubled = value * 2;
    console.log(`Doubled Value: ${doubled}`);
  });

  constructor() {
    this.logDoubledValue(this.counter);
  }

  increment() {
    this.counter.set(this.counter() + 1);
  }
}

Here, logDoubledValue is invoked whenever the increment method is called. The counter’s value is passed into the signalMethod, which then logs the doubled value. This example shows how easily signalMethod integrates with signals to react to state changes.

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Reacting to Signals Dynamically

Suppose you’re working on a temperature monitoring system. Instead of logging doubled values, you need to alert the user if the temperature exceeds a threshold. With signalMethod, this becomes straightforward:

@Component({
  selector: 'app-temperature-monitor',
  template: `<button (click)="increaseTemperature()">Increase Temperature</button>`
})
export class TemperatureMonitorComponent {
  private temperature = signal(20); // Start at 20°C

  readonly alertHighTemperature = signalMethod<number>((temp) => {
    if (temp > 30) {
      console.warn('Warning: High temperature detected!');
    }
  });

  constructor() {
    this.alertHighTemperature(this.temperature);
  }

  increaseTemperature() {
    this.temperature.set(this.temperature() + 5);
  }
}

Every time the temperature increases, the alertHighTemperature method evaluates the new value and issues a warning if it’s too high.

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Controlling Cleanup for Services

In some cases, you might define signalMethod in a service rather than directly in a component. This allows for better reuse but requires careful management of side effects to avoid memory leaks.

Here’s an example:

import { Injectable } from '@angular/core';
import { signalMethod } from '@ngrx/signals';

@Injectable({ providedIn: 'root' })
export class ScoreService {
  readonly logScore = signalMethod<number>((score) => {
    console.log(`Current Score: ${score}`);
  });
}

Now, suppose a component uses this service:

@Component({
  selector: 'app-score-tracker',
  template: `<button (click)="updateScore()">Update Score</button>`
})
export class ScoreTrackerComponent {
  private scoreService = inject(ScoreService);

  private score = signal(0);

  constructor() {
    this.scoreService.logScore(this.score);
  }

  updateScore() {
    this.score.set(this.score() + 10);
  }
}

To prevent memory leaks, make sure to inject the component’s context when using the service in dynamic scenarios:

import { Injector } from '@angular/core';

@Component({ /* ... */ })
export class ScoreTrackerComponent {
  private injector = inject(Injector);
  private scoreService = inject(ScoreService);

  private score = signal(0);

  constructor() {
    this.scoreService.logScore(this.score, { injector: this.injector });
  }

  updateScore() {
    this.score.set(this.score() + 10);
  }
}

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Why Choose signalMethod?

Compared to other tools like effect, signalMethod offers some distinct advantages:

1. Flexibility: It can process both static values and reactive signals, making it ideal for mixed scenarios.
2. Explicit Dependency Tracking: Tracks only the provided signal, reducing the risk of unintended dependencies.
3. Simplified Context Management: Works seamlessly in Angular injection contexts and allows manual control when needed.

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A Note on When to Use signalMethod

While signalMethod is perfect for handling straightforward side effects in reactive workflows, there are scenarios where RxJS might be a better fit—especially for complex streams or cases involving race conditions. However, for applications leveraging NgRx signals, signalMethod strikes a perfect balance of simplicity and power.

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Final Thoughts

NgRx’s signalMethod is a game-changer for handling side effects in Angular applications. By combining the elegance of signals with the flexibility of processor functions, it simplifies reactive patterns while maintaining control over cleanup and dependencies.

If you’re using NgRx Signals in your projects, I highly recommend exploring signalMethod to streamline your side-effect handling. Try it out and experience how it can make your Angular applications cleaner and more reactive!

Comments

[Kobi Hari]

I don't think you are supposed to call the signal method every time you increment the counter, since you are passing the signal by reference. You should only call it once in the constructor, and then whenever the signal changes, the method will be invoked automatically.

[Daniel Sogl]

Hi Kobi, thanks for your comment. You are right. You can and maybe should call the function once in the constructor to react to the changes like with the rxMethod. I updated the article to make it more clear