Make directive @Input required

Question

In AngularJs we could make a directive attribute required. How do we do that in Angular with @Input? The docs don\'t mention it.

Eg.

@Component({
  selec         


        

Answer 1

For me, I had to do it this way:

ngOnInit() {
    if(!this.hasOwnProperty('a') throw new Error("Attribute 'a' is required");
}

FYI, If you want to require @Output directives, then try this:

export class MyComponent {
    @Output() myEvent = new EventEmitter(); // This a required event

    ngOnInit() {
      if(this.myEvent.observers.length === 0) throw new Error("Event 'myEvent' is required");
    }
}