Redux Observable:如果同一个操作被多次调度，我如何取消其中的一个？

import { ofType } from 'redux-observable';
import { mergeMap, takeUntil } from 'rxjs/operators';
import { of, timer } from 'rxjs';

// 定义一个 action 类型
const FETCH_DATA = 'FETCH_DATA';

// 定义一个 action 创建函数
const fetchData = () => ({ type: FETCH_DATA });

// 定义一个异步操作的 epic
const fetchDataEpic = action$ =>
  action$.pipe(
    ofType(FETCH_DATA),
    mergeMap(action =>
      // 模拟异步操作
      timer(1000).pipe(
        takeUntil(action$.pipe(ofType(FETCH_DATA)))
      )
    ),
    mergeMap(() => of({ type: 'FETCH_DATA_SUCCESS' }))
  );

// 使用 Redux Observable 创建 store
const { createStore, applyMiddleware } = Redux;
const { createEpicMiddleware } = ReduxObservable;

const epicMiddleware = createEpicMiddleware();

const store = createStore(reducer, applyMiddleware(epicMiddleware));

epicMiddleware.run(fetchDataEpic);

// 调度多次 FETCH_DATA 操作
store.dispatch(fetchData());
store.dispatch(fetchData());
store.dispatch(fetchData());