对象键“未定义”[重复]

Question

我从一个API获得一个对象，并在它里面用其他API响应创建新的对象，例如：

API响应1:obj:{A:1,B:2}

API响应2:3

console.log(Obj) return Obj: {a: 1, b: 2, c: 3}

console.log(Obj.c) return undefined

当我试图在属性的.map之后给出console.log时，我无法访问创建的属性，返回undefined。但是，当我为任何对象提供console.log时，所创建的属性就在那里。

async getGeneralInfo(token, seed) {
    try {
        API_HEADER.headers.Authorization = token;
        let responseAvaliableCoins = await axios.get(
            BASE_URL + "/coin",
            API_HEADER
        );

        let avaliableCoins = responseAvaliableCoins.data.data.coins;

        avaliableCoins.map(async (coin, index) => {
            if (coin.status === "active") {
                let responseCreateAddress = await axios.post(
                    BASE_URL + "/coin/" + coin.abbreviation + "/address",
                    { seed },
                    API_HEADER
                );

                avaliableCoins[index].address =
                    responseCreateAddress.data.data.address;

                let responseBalance = await axios.get(
                    BASE_URL +
                    "/coin/" +
                    coin.abbreviation +
                    "/balance/" +
                    coin.address,
                    API_HEADER
                );

                avaliableCoins.token = responseBalance.headers[HEADER_RESPONSE];
                avaliableCoins[index].balance = responseBalance.data.data;
            } else {
                avaliableCoins[index].address = undefined;
                avaliableCoins[index].balance = undefined;
            }
        });

        console.warn(avaliableCoins[0].balance); //undefined
        console.warn(avaliableCoins[0]["balance"]); //undefined
        console.warn(avaliableCoins[0].address); //undefined
        console.warn(avaliableCoins[0]["address"]); //undefined

        console.warn("avaliableCoins", avaliableCoins); //All objects are here
        console.warn("avaliableCoins[0]", avaliableCoins[0]); //All objects are here

        return avaliableCoins;
    } catch (error) {
        internalServerError();
        return;
    }
}

Answer 1

map中使用的函数是异步的。

现在正在对所有硬币调用map，在所有异步数据返回之前，代码已经转移到控制台。warn()调用。

AvailableCoins最终将在返回时使用所有异步数据进行更新，但是这里存在争用条件，因为代码没有显式地等待这种情况发生。

null

下面是一个简化版本，它取消了这种方法：

const getData = () => {
  return Promise.resolve('data');
}

export const getGeneralInfo = async () => {
  let avaliableCoins = [
    { a: 1 },
    { a: 2 }
  ]

  const promises = avaliableCoins.map(async (coin) => {
    let response = await getData();
    // modify coin and return it
    coin.data = response;
    return coin;
  });

  const updatedCoins = await Promise.all(promises);

  console.log(updatedCoins); // [{a: 1, data: 'data'}, {a: 2, data: 'data'}]

  return updatedCoins;
}

修改后的函数如下所示：

async getGeneralInfo(token, seed) {
  try {
    API_HEADER.headers.Authorization = token;
    let responseAvaliableCoins = await axios.get(
      BASE_URL + "/coin",
      API_HEADER
    );

    let avaliableCoins = responseAvaliableCoins.data.data.coins;

    const promises = avaliableCoins.map(async (coin) => {
      if (coin.status === "active") {
        let responseCreateAddress = await axios.post(
          BASE_URL + "/coin/" + coin.abbreviation + "/address",
          { seed },
          API_HEADER
        );

        coin.address =
          responseCreateAddress.data.data.address;

        let responseBalance = await axios.get(
          BASE_URL +
          "/coin/" +
          coin.abbreviation +
          "/balance/" +
          coin.address,
          API_HEADER
        );

        coin.token = responseBalance.headers[HEADER_RESPONSE];
        coin.balance = responseBalance.data.data;
      } else {
        coin.address = undefined;
        coin.balance = undefined;
      }
      return coin;
    });

    availableCoins = await Promise.all(promises);

    console.warn(avaliableCoins[0].balance); //undefined
    console.warn(avaliableCoins[0]["balance"]); //undefined
    console.warn(avaliableCoins[0].address); //undefined
    console.warn(avaliableCoins[0]["address"]); //undefined

    console.warn("avaliableCoins", avaliableCoins); //All objects are here
    console.warn("avaliableCoins[0]", avaliableCoins[0]); //All objects are here

    return avaliableCoins;
  } catch (error) {
    internalServerError();
    return;
  }
}