Signal-based components in Angular 17

Signal-based components are a new feature in Angular 17 that provide a more efficient and predictable way to write reactive code. Signal-based components are built on top of Angular's existing reactivity model, but they provide a number of enhancements that make them easier to use and more performant.

Benefits of signal-based components

Signal-based components offer a number of benefits over traditional Angular components:

• Predictable performance: Signal-based components only re-render when their inputs change. This can lead to significant performance improvements, especially for complex applications.
• Cleaner code: Signal-based components make it easier to write code that is both reactive and easy to understand. This is because inputs are read-only inside signal-based components, which helps to prevent accidental state mutation.
• Better debugging: Signal-based components make it easier to debug reactive applications. This is because signal emissions are logged to the console, which can help you to track down the source of any problems.

How to create a signal-based component

To create a signal-based component, simply set the signals: true property in the component decorator. Angular will then automatically manage the lifecycle of your component's inputs and outputs, and you can be confident that your component will only re-render when its inputs change.

For example, the following code defines a simple signal-based component with a single input and output:

@Component({
  selector: 'my-signal-based-component',
  signals: true,
})
export class MySignalBasedComponent {
  @Input() input$: Observable<number>;

  @Output() output$ = new Subject<number>();

  constructor() {}

  ngOnInit() {
    this.input$.subscribe(value => {
      this.output$.next(value * 2);
    });
  }
}

Using signal-based components

To use a signal-based component, simply bind its outputs to elements in your template. For example, the following code binds the output$ output of the MySignalBasedComponent component to a text element:

<my-signal-based-component (output$)="myOutput($event)"></my-signal-based-component>

When the input$ input to the component changes, the output$ output will be emitted, and the text element will be updated with the new value.

Signal-based queries

Signal-based components also provide a new type of query called signal-based queries. Signal-based queries allow you to subscribe to the results of a view query and receive the results as a signal. This can be useful for updating the state of your component based on changes to the DOM.

For example, the following code uses a signal-based query to subscribe to the changes to the text of an input element:

@Component({
  selector: 'my-signal-based-component',
  signals: true,
})
export class MySignalBasedComponent {
  @Input() input$: Observable<string>;

  @Output() output$ = new Subject<string>();

  constructor() {}

  ngOnInit() {
    this.input$ = this.query('input').changes;

    this.input$.subscribe(value => {
      this.output$.next(value);
    });
  }
}

When the user changes the text of the input element, the input$ signal will be emitted with the new value.

Conclusion

Signal-based components are a powerful new feature in Angular 17 that can help you to write more efficient, predictable, and debuggable reactive code. By understanding the basics of signal-based components, you can start to take advantage of their benefits in your own applications.

Here are some additional tips for using signal-based components:

• Use signal-based queries to subscribe to the results of view queries and update the state of your component based on changes to the DOM.
• Use signal-based inputs and outputs to create components that are more reactive and easier to debug.
• Use signal-based components in conjunction with Angular's existing reactivity model to build complex and powerful applications.

**Signal-based components are still a relatively new feature in Angular, but they have the potential to revolutionize the way that we write reactive Angular applications. By understanding the basics of signal-based components, you can start to take advantage of their benefits in your own applications.

• Date: 08 Nov 2023