@input and @output in angular 8 code example

Example 1: send event to child component angular

Parent-Component

eventsSubject: Subject<void> = new Subject<void>();

emitEventToChild() {
  this.eventsSubject.next();
}


Parent-HTML

<child [events]="eventsSubject.asObservable()"> </child>


Child-Component

private eventsSubscription: Subscription;

@Input() events: Observable<void>;

ngOnInit(){
  this.eventsSubscription = this.events.subscribe(() => doSomething());
}

ngOnDestroy() {
  this.eventsSubscription.unsubscribe();
}

Example 2: output event angular

@Component({...})
export class CounterComponent {

  @Input()
  count: number = 0;

  @Output()
  change: EventEmitter<number> = new EventEmitter<number>();

  increment() {
    this.count++;
    this.change.emit(this.count);
  }

  decrement() {
    this.count--;
    this.change.emit(this.count);
  }

  	// in parent component
	//(change)="countChange($event)"> 

}