React代码报错：undefined is not an object (evaluating 'pray.findIndex')

运行以下React代码时出现错误：undefined is not an object (evaluating 'pray.findIndex')

代码如下：

const [pray, setPray] = useState([]);
const fetchPray = async county => {
 const url4 = '-' + county;
 console.log(url4);
 fetch(url4)
.then(response => response.json())
.then(json => setPray(json))
.then(pray => {
  let index = pray.findIndex(d => d.MiladiTarihKisa === date);
  let selectData = pray[index];

  setVakitGunes(selectData.Gunes);
  setVakitImsak(selectData.Imsak);
  setVakitOgle(selectData.Ogle);
  setVakitIkindi(selectData.Ikindi);
  setVakitAksam(selectData.Aksam);
  setVakitYatsi(selectData.Yatsi);
  setGunTurkce(selectData.MiladiTarihUzun);
})
.catch(error => console.log(error))
.finally(() => setLoading4(false));
};

• 核心原因：setPray(json)是异步更新状态的操作，且后续.then(pray => { ... })中的pray参数并非更新后的状态值——setPray本身无返回值，所以此处pray为undefined，调用findIndex必然报错。

• 修复方案：

  1. 直接使用接口返回的json数据处理逻辑，无需依赖异步更新的状态：

     const [pray, setPray] = useState([]);
     const fetchPray = async county => {
      const url4 = '-' + county;
      console.log(url4);
      fetch(url4)
     .then(response => response.json())
     .then(json => {
        setPray(json);
        // 直接用接口返回的json数据处理
        let index = json.findIndex(d => d.MiladiTarihKisa === date);
        // 增加判断，避免匹配不到数据时出现新错误
        if (index !== -1) {
          let selectData = json[index];
          setVakitGunes(selectData.Gunes);
          setVakitImsak(selectData.Imsak);
          setVakitOgle(selectData.Ogle);
          setVakitIkindi(selectData.Ikindi);
          setVakitAksam(selectData.Aksam);
          setVakitYatsi(selectData.Yatsi);
          setGunTurkce(selectData.MiladiTarihUzun);
        }
     })
     .catch(error => console.log(error))
     .finally(() => setLoading4(false));
     };
     

  2. 额外优化：添加index !== -1的判断，防止当date无匹配数据时，selectData为undefined引发新的报错。

内容的提问来源于stack exchange，提问作者sweoguzhan