循环数组问题

Question

我正在调用一个返回数组的API，我试图遍历这个数组，但控制台说的是长度为0，以前从未见过类似的东西，无法在这里找出问题所在：

const funCall=async()=>{

      const userNFTsURLs = await prepareData();
      setNFTsUrls(userNFTsURLs);
}

  const prepareData = async () => {
    const res = await getUserNFTs();
    console.log(res);
/*returns 
0: "ipfs://QmbNHPexuZWo3rnzAyyzZxTsAmMuN97R8Z7qwuPfEMXeX9/4.json"
1: "ipfs://QmbNHPexuZWo3rnzAyyzZxTsAmMuN97R8Z7qwuPfEMXeX9/41.json"
2: "ipfs://QmbNHPexuZWo3rnzAyyzZxTsAmMuN97R8Z7qwuPfEMXeX9/45.json"
3: "ipfs://QmbNHPexuZWo3rnzAyyzZxTsAmMuN97R8Z7qwuPfEMXeX9/47.json"
4: "ipfs://QmbNHPexuZWo3rnzAyyzZxTsAmMuN97R8Z7qwuPfEMXeX9/49.json"
5: "ipfs://QmbNHPexuZWo3rnzAyyzZxTsAmMuN97R8Z7qwuPfEMXeX9/51.json"
length: 6
[[Prototype]]: Array(0)*/

    console.log(res.length);//returns 0


    res.map((rest: string) => console.log(rest));
    const test = res.map((url: string) => {
console.log(url)//does not return anything is not being called
      return url;
    });

    return res;
  };

函数，我只是控制台记录了最后一个forEach，它在登录到使用它的组件上之后会对它进行日志记录，这是非常奇怪的。

 const getUserNFTs = async () => {
    if (store.getState().blockChain.smartContract === null) {
      await connectToContract();
    }
    try {
      const balance = await getUserTokensBalance();
      if (balance <= 0) {
        return [];
      }
      let tokenIds = [];
      for (let i = 0; i < balance; i++) {
        const tokenId = await blockChain.smartContract.methods
          .tokenOfOwnerByIndex(walletId, i)
          .call();
        tokenIds.push(tokenId);
      }

      let tokensList: any = [];

      tokenIds.forEach(async (tokenId) => {
        const token = await blockChain.smartContract.methods
          .tokenURI(tokenId)
          .call();
        console.log("token", token);//logs it on console after logs al the other console logs

        tokensList.push(token);
      });

      return tokensList;
    } catch (error) {
      console.log(error);
    }
  };

我有什么没拿到的？经过几个小时的努力，我感到非常沮丧

Answer 1

您的问题是您使用的是forEach，它没有像您预期的那样等待结果。

您应该将其修改为通常的for循环，以消除forEach中的async回调函数。

for(const tokenId of tokenIds) {
        const token = await blockChain.smartContract.methods
          .tokenURI(tokenId)
          .call();
        console.log("token", token);//logs it on console after logs al the other console logs

        tokensList.push(token);
};