从 then() 返回数据返回 Promise<void> 而不是 Promise<data>答案

【问题标题】：returning data from then() returns Promise<void> instead of Promise<data>从 then() 返回数据返回 Promise<void> 而不是 Promise<data>
【发布时间】：2021-03-17 09:29:25
【问题描述】：

我从 API 获取数据如下：

export const getSymbolStats = async (symbol: string) => {
let requiredData: IRequiredSymbolStats;
let request: Promise<AxiosResponse> = axios.get(`${api.baseURL}${api.symbolStats}`, {params: {symbol}});

request.then((res: AxiosResponse<ISymbolStats>) => {
    const symbolStats: ISymbolStats = res.data;

    // Destructure symbol stats.
    const highPrice: string = symbolStats.highPrice;
    const lowPrice: string = symbolStats.lowPrice;
    const priceChangePercent: string = symbolStats.priceChangePercent;
    const volume: string = symbolStats.volume;
    const weightedAvgPrice: string = symbolStats.weightedAvgPrice;

    // return an object with the required data.

    requiredData = {
        symbol,
        highPrice,
        lowPrice,
        priceChangePercent,
        volume,
        weightedAvgPrice,
    };
    return requiredData;
})
}

并在此函数中检索数据：

export const getStats = async (msg: Message, match: RegExpExecArray | null): Promise<void> => {
  const id = msg.chat.id;
  const symbol: OrUndefined<string> = validateSymbol(id, match);
  if (!symbol) return;

  // make API call to get stats for symbol.
  let data = await getSymbolStats(symbol);

};

第二个函数中的data 显示void，而不是我在then() 块中返回的IRequiredSymbolStats 类型。这是为什么呢？

【问题讨论】：

你为什么在async function中使用then？

标签： typescript promise async-await es6-promise

【解决方案1】：

如果您将函数声明为async，则无需使用 then。
你从then返回的东西无处可去，因为你不存储也不从getSymbolStats返回它

只需使用await 并存储结果或在request.then 之前添加return。

使用await（更直接的代码，我更喜欢这种方式）。

const res: AxiosResponse<ISymbolStats> = await axios.get<ISymbolStats>(`${api.baseURL}${api.symbolStats}`, {params: {symbol}});

const symbolStats: ISymbolStats = res.data;

// Destructure symbol stats.
const highPrice: string = symbolStats.highPrice;
const lowPrice: string = symbolStats.lowPrice;
const priceChangePercent: string = symbolStats.priceChangePercent;
const volume: string = symbolStats.volume;
const weightedAvgPrice: string = symbolStats.weightedAvgPrice;

// return an object with the required data.

requiredData = {
  symbol,
  highPrice,
  lowPrice,
  priceChangePercent,
  volume,
  weightedAvgPrice,
};
return requiredData;

添加return:

let request: Promise<AxiosResponse> = axios.get(`${api.baseURL}${api.symbolStats}`, {params: {symbol}});

return request.then((res: AxiosResponse<ISymbolStats>) => {
    const symbolStats: ISymbolStats = res.data;

    // Destructure symbol stats.
    const highPrice: string = symbolStats.highPrice;
    const lowPrice: string = symbolStats.lowPrice;
    const priceChangePercent: string = symbolStats.priceChangePercent;
    const volume: string = symbolStats.volume;
    const weightedAvgPrice: string = symbolStats.weightedAvgPrice;

    // return an object with the required data.

    requiredData = {
        symbol,
        highPrice,
        lowPrice,
        priceChangePercent,
        volume,
        weightedAvgPrice,
    };
    return requiredData;
})

【讨论】：