Angular 19’s Signal-Based Inputs: A Simpler Alternative to @Input()

Angular 19 improved signal-based inputs for production, a new feature that enhances reactivity and simplifies component development compared to the traditional @Input decorator. This is an overview of this feature:

What Are Signal-Based Inputs?

Signal inputs are a reactive alternative to the @Input decorator for passing data from parent components to child components. Instead of directly assigning values, signal inputs use a wrapper function (input()) to create signals that automatically propagate changes to child components. This approach eliminates the need for lifecycle hooks like ngOnChanges or manual input setters, making the code more declarative and less error-prone[1][2][3].

Key Features

1. Reactive by Default: Signal inputs automatically update when their values change, simplifying state management[2][3].
2. Type Safety: Signals are strongly typed, ensuring better type checking during development[6].
3. Computed Properties: Developers can use computed signals to react dynamically to input changes without additional boilerplate[5][6].
4. Options for Inputs:
   • Required Inputs: Enforce mandatory inputs using input.required()[1][7].
   • Aliases: Define alternative names for inputs using { alias: 'name' }[4][7].
   • Transforms: Apply transformations to input values before use, such as converting strings to uppercase[1][4].

Advantages Over @Input Decorator

• Eliminates the need for lifecycle hooks like ngOnChanges.
• Reduces boilerplate code by handling reactivity implicitly.
• Provides better performance and scalability in applications with complex data flows[1][2][5].

Using Signal-Based Inputs

To define signal-based inputs in Angular 19, use the input() function instead of @Input. Here’s an example:

@Component({
  selector: 'counter',
  standalone: true,
  template: `The counter value is `,
})
export class CounterComponent {
  counter = input.required(); // Required signal input
}

Migration from @Input

Angular provides a migration tool (ng generate @angular/core:signal-input) to convert existing @Input decorators into signal-based inputs automatically[1].

Conclusion

Signal-based inputs are a significant step forward in Angular's journey toward full application-wide reactivity. They simplify component development, improve performance, and enable developers to write cleaner and more maintainable code. While the traditional @Input decorator is still supported, signal-based inputs are now the recommended approach for new components[3][7].

[1] https://www.youtube.com/watch?v=bTc_NMhKOMY [2] https://javascript.plainenglish.io/read-this-before-upgrading-to-signal-inputs-in-angular-19-1f1ba5b7c308?gi=c8f54f43f1f8 [3] https://blog.angular-university.io/angular-signal-components/ [4] https://dev.to/this-is-angular/be-ready-for-input-signals-in-angular-3djf [5] https://angularexperts.io/blog/angular-signal-inputs/ [6] https://www.youtube.com/watch?v=yjCeaiWXC0U [7] https://blog.angular-university.io/angular-signal-inputs/ [8] https://angular.dev/guide/signals/inputs/