managing-state-naive.ts

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

export function debug<T>(): MonoTypeOperatorFunction<T> {
  let index = -1;
  // Let's pretend that the map operator doesn't exist and that we have to use
  // the tap operator and maintain our own internal state for the index, as the
  // purpose of our operator is to show that the behaviour depends upon where
  // the state is stored.
  return tap(t => console.log(`[${++index}]: ${t}`));
}