block11.javascript

const fetch = require('node-fetch');

// ...

const fetchEpic = action$ => action$.pipe(
  filter(action => action.type === 'FETCH_STOCK_PRICE'),
  mergeMap(async (action) => {
    const url = `https://api.iextrading.com/1.0/stock/${action.symbol}/price`;
    const price = await fetch(url).then(res => res.text());
    return Object.assign({}, action, { type: 'FETCH_STOCK_PRICE_SUCCESS', price });
  }),
  catchError(err => Promise.resolve({ type: 'FETCH_STOCK_PRICE_ERROR', message: err.message }))
);