How to use the @reactivex/ix-es2015-cjs/asynciterable/concat.concat function in @reactivex/ix-es2015-cjs

public concat(
    other: StackItemEnumerator,
  ): StackItemEnumerator {
    const iterable = concat(
      AsyncIterableX.from(this.enumerator as AsyncIterableIterator),
      AsyncIterableX.from(other.enumerator as AsyncIterableIterator),
    );

    return new StackItemEnumerator(iterable[Symbol.asyncIterator]());
  }
}

public concatIterator(other: StackItemIterator): StackItemIterator {
    const iterable = concat(
      AsyncIterableX.from(this.enumerator as AsyncIterableIterator),
      AsyncIterableX.from(other.enumerator as AsyncIterableIterator),
    );

    return new StackItemIterator(iterable[Symbol.asyncIterator]());
  }
}