Use in components with the @Output directive to emit custom events synchronously or asynchronously, and register handlers for those events by subscribing to an instance.

class EventEmitter<T> extends Subject {
  constructor(isAsync?: boolean): EventEmitter<T>
  emit(value?: T): void
  subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void): Subscription
}

See also

• Observables in Angular

Constructor

Creates an instance of this class that can deliver events synchronously or asynchronously.

constructor(isAsync?: boolean): EventEmitter<T> Parameters isAsync boolean When true, deliver events asynchronously. Optional. Default is false. Returns EventEmitter<T>

Methods

emit()
Emits an event containing a given value.
emit(value?: T): void Parameters value T The value to emit. Optional. Default is undefined. Returns void

subscribe()
Registers handlers for events emitted by this instance.
subscribe(observerOrNext?: any, error?: any, complete?: any): Subscription Parameters observerOrNext any When supplied, a custom handler for emitted events, or an observer object. Optional. Default is undefined. error any When supplied, a custom handler for an error notification from this emitter. Optional. Default is undefined. complete any When supplied, a custom handler for a completion notification from this emitter. Optional. Default is undefined. Returns Subscription

Usage notes

Extends RxJS Subject for Angular by adding the emit() method.

In the following example, a component defines two output properties that create event emitters. When the title is clicked, the emitter emits an open or close event to toggle the current visibility state.

@Component({
  selector: 'zippy',
  template: `
  <div class="zippy">
    <div (click)="toggle()">Toggle</div>
    <div [hidden]="!visible">
      <ng-content></ng-content>
    </div>
 </div>`})
export class Zippy {
  visible: boolean = true;
  @Output() open: EventEmitter<any> = new EventEmitter();
  @Output() close: EventEmitter<any> = new EventEmitter();

  toggle() {
    this.visible = !this.visible;
    if (this.visible) {
      this.open.emit(null);
    } else {
      this.close.emit(null);
    }
  }
}

Access the event object with the $event argument passed to the output event handler:

<zippy (open)="onOpen($event)" (close)="onClose($event)"></zippy>