Class OutputEmitterRef

packages/core/src/authoring/output/output_emitter_ref.ts:33–121

 * @publicAPI
 */
export class OutputEmitterRef<T> implements OutputRef<T> {
  private destroyed = false;
  private listeners: Array<((value: T) => void) | null> | null = null;
  private errorHandler = inject(ErrorHandler, {optional: true});
  private isEmitting = false;
  private hasNullListeners = false;

  /** @internal */
  destroyRef: DestroyRef = inject(DestroyRef);

  constructor() {
    // Clean-up all listeners and mark as destroyed upon destroy.
    this.destroyRef.onDestroy(() => {
      this.destroyed = true;
      this.listeners = null;
    });
  }

  subscribe(callback: (value: T) => void): OutputRefSubscription {
    if (this.destroyed) {
      throw new RuntimeError(
        RuntimeErrorCode.OUTPUT_REF_DESTROYED,
        ngDevMode &&
          'Unexpected subscription to destroyed `OutputRef`. ' +
            'The owning directive/component is destroyed.',
      );
    }

    (this.listeners ??= []).push(callback);

    return {
      unsubscribe: () => {
        const index = this.listeners ? this.listeners.indexOf(callback) : -1;
        if (index > -1) {
          // If we try to unsubscribe while an `emit` is happening, we can throw off the loop.
          // Replace the listener with null so we can clean it up later. Note that it would be
          // simpler to clone the array when iterating over it, but we're trying to avoid cloning
          // since unsubscribing from within the event should be fairly uncommon.
          if (this.isEmitting) {
            this.hasNullListeners = true;
            this.listeners![index] = null;
          } else {
            this.listeners!.splice(index, 1);
          }
        }
      },
    };
  }

  /** Emits a new value to the output. */
  emit(value: T): void {
    if (this.destroyed) {
      console.warn(
        formatRuntimeError(
          RuntimeErrorCode.OUTPUT_REF_DESTROYED,
          ngDevMode &&
            'Unexpected emit for destroyed `OutputRef`. ' +
              'The owning directive/component is destroyed.',