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EventEmitter

class

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 = false)
  emit(value?: T)
  subscribe(generatorOrNext?: any, error?: any, complete?: any): Subscription
}

See also

Constructor

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

constructor(isAsync: boolean = false)

Parameters
isAsync boolean

When true, deliver events asynchronously.

Optional. Default is false.

Methods

Emits an event containing a given value.

emit(value?: T)

Parameters
value T

The value to emit.

Optional. Default is undefined.

Registers handlers for events emitted by this instance.

subscribe(generatorOrNext?: any, error?: any, complete?: any): Subscription

Parameters
generatorOrNext any

When supplied, a custom handler for emitted events.

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>

© 2010–2019 Google, Inc.
Licensed under the Creative Commons Attribution License 4.0.
https://angular.io/api/core/EventEmitter