managing-state-observable.ts

import { MonoTypeOperatorFunction, Observable } from "rxjs";
import { tap } from "rxjs/operators";

export function debug<T>(): MonoTypeOperatorFunction<T> {
  return source => new Observable<T>(subscriber => {
    let index = -1;
    return source.pipe(
      tap(t => console.log(`[${++index}]: ${t}`))
    ).subscribe(subscriber);
  });
}