如何返回 Promise 的值，而不是返回 Promise 本身？ （反应/Redux）[重复]

Question

我在我的一个 reducer 中遇到问题，我可以随时返回前端的所有信息，除了一个名为“items”的数组，我需要进行额外的提取以获取更多数据.我在这个 fetch 中遇到的问题是它最终导致返回一个承诺而不是返回值。我的问题是如何获得价值而不是承诺？ （例如，通过阻止其他所有内容，直到 promise 解决，然后将其发回）。

我在下面的代码中进行了评论，希望能更清楚地解释一切：

export const getItemsForHistory = createSelector(
    [getAllHistory, getAllItems, getHistoryPage], (history, items, page) => {
        let itemIds = `[a bunch of ids]`;

        //this is the call I am making to fetch the additional data for "items"
        //this return statement is sending back a promise and not a value
        return getUpdatedItems(itemIds, items).then(result => {
            //result is the actual value I want
            return result;
        }, error => {
            //if the fetch fails, I would like to send a default value for "items"
            //note, if I place this return outside of this entire promise and remove the promise, it works as expected with the default data
            return history.map(h => items.get(h.get('item'), null))
        }).catch(error => {
            return history.map(h => items.get(h.get('item'), null))
        })
    }
)

//I would like for this method to run asychronously
const getUpdatedItems = async (itemIds, items) => {
    let result = await fetchHistoryItemsDetail(itemIds);
    return result;
}

const fetchHistoryItemsDetail = (itemIds) => {
    let headers = {
            "Content-Type": "application/json",
        },
        fetchUrl = `XXXXXXXXX`;
    return fetch(fetchUrl, {
        method: "POST",
        headers: headers,
        body: itemIds,
        withCredentials: true,
        crossDomain: true,
    })
        .then(response => {
            return response.json();
        })
        .catch(error => {
            throw error;
        })
}

export const getSortedHistory = createSelector(
    [getAllHistory, getItemsForHistory, getHistorySort, getHistoryPage], (history, items, sort, page) => {
        //this is where items is ultimately retured to the front end but it is now a promise and not an array of data
        //(from getItemsForHistory)
        return sortedEntities(history, items, sort)
    }
)

我希望我的问题很清楚，但如果需要进一步详细说明，请告诉我。

Answer 1

您不能从 Promise 的猫/错误处理程序中返回数据

如果你想同时发送数据，我建议包装另一个承诺，该承诺将始终解决

return new Promise((res) => {
  //this is the call I am making to fetch the additional data for "items"
  //this return statement is sending back a promise and not a value
  getUpdatedItems(itemIds, items).then(result => {
    //result is the actual value I want
    res(result);
  }, error => {
    //if the fetch fails, I would like to send a default value for "items"
    //note, if I place this return outside of this entire promise and remove the promise, it works as expected with the default data
    res(history.map(h => items.get(h.get('item'), null)));
  }).catch(error => {
    res(history.map(h => items.get(h.get('item'), null)));
  })
});