tapIndex rxjs operator

tap-index.ts

class TapIndexSubscriber<T> extends Subscriber<T> {

  private count: number = 0;

  constructor(
    protected destination: Subscriber<T>,
    private nextEmit: (value: T, index: number) => void
  ) {
    super(destination);
  }

  protected _next(value: T): void {
    this.nextEmit(value, this.count++);
    this.destination.next(value);
  }

}

class TapIndexOperator<T> implements Operator<T, T> {

  constructor(private nextEmit: (value: T, index: number) => void) { }

  public call(subscriber: Subscriber<T>, source: Subscribable<T>): TeardownLogic {
    return source.subscribe(new TapIndexSubscriber(subscriber, this.nextEmit));
  }

}

export function tapIndex<T>(nextEmit: (value: T, index: number) => void): MonoTypeOperatorFunction<T> {
  return function tapIndexOperation(source: Observable<T>): Observable<T> {
    return source.lift(new TapIndexOperator(nextEmit));
  };
}