Angular 2+ - check if Pipe returns an empty subset of original list

Question

I have a list of strings that I want to iterate through, but I want to be able to filter them using a search term. Like this:

Answer 1

It's possible to leverage dependency injection into pipes. You could inject the component:

Then you can set a property on it to notify this:

@Pipe({
  name: 'search'
})
export class SearchPipe {
  constructor(@Inject(forwardRef(() => SomeComponent)) private comp:SomeComponent) {

  }

  transform(value) {
    var filtered = value.map((v) => v-1);
    this.comp.isEmpty = (filtered.length === 0);
    return filtered;
  }
}

The main drawback is that you link the pipe within the component. The advantage is that filtering is executed once.