Angular Signals - computed signal based on input

Question

I'm asking for opinions about my use-case.

very simplified example:

@Input() parentComponent;
childSignal = computed(() => this.parentComponent.parentSignal());

This code will throw runtime error because parentComponent is undefined when signal gets computed for the first time.

Now what would be your way? Initializing signal in ngOnChanges?

Are you facing any issue when using the approach mentioned above? — Chellappan வ, May 19 '23 at 13:59
This code will throw runtime error because parentComponent is undefined when signal gets computed for the first time. — George Knap, May 19 '23 at 14:03
Since computed signals "recovers" It should be fine i guess.this.parentComponent?.parentSignal() — Chellappan வ, May 19 '23 at 14:04

score 0 · Answer 1 · answered Jul 17 '23 at 17:27

We will eventually get { signal: true } components that have real Signal inputs.

For now (until this feature exists) the simplest approach is to:

Create a signal that is updated in ngOnChanges.

@Input('userId')
userId: string;

ngOnChanges(changes: SimpleChanges)
{
   this.userIdSignal.set(this.userId); 
}

userIdSignal = signal(null);

1 Answers1