share-replay-log.ts

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

export const log = <T>(source: Observable<T>, name: string) => defer(() => {
  console.log(`${name}: subscribed`);
  return source.pipe(
    tap({
      next: value => console.log(`${name}: ${value}`),
      complete: () => console.log(`${name}: complete`)
    }),
    finalize(() => console.log(`${name}: unsubscribed`))
  );
});