英文:
Error: Can not read property 'map' of undefined error In React Mongo DB
问题
After executing my React code, I got the following error message in the browser console: "TypeError: Cannot read property 'map' of undefined". here is my code:
const MyComponent = () => {
const [data, setData] = useState([]);
useEffect(() => {
fetchData();
}, []);
const fetchData = async () => {
const response = await fetch('https://api.example.com/data');
const jsonData = await response.json();
setData(jsonData);
};
return (
<div>
{data.map((item) => (
<div key={item.id}>{item.name}</div>
))}
</div>
);
};
export default MyComponent;
英文:
After executing my React code, I gotthe following error message in the browser console: "TypeError: Cannot read property 'map' of undefined". here is my code
const MyComponent = () => {
const [data, setData] = useState([]);
useEffect(() => {
fetchData();
}, []);
const fetchData = async () => {
const response = await fetch('https://api.example.com/data');
const jsonData = await response.json();
setData(jsonData);
};
return (
<div>
{data.map((item) => (
<div key={item.id}>{item.name}</div>
))}
</div>
);
};
export default MyComponent;
答案1
得分: 1
我建议您使用 try...catch 来处理可能出现的请求错误，以确保您的应用程序不会崩溃。示例代码如下：
const fetchData = async () => {
try {
const response = await fetch('https://api.example.com/data');
const jsonData = await response.json();
setData(jsonData);
}
catch (error) {
// 如果请求返回错误...
setData([]);
}
}
如果错误仍然存在，可能是您的请求没有错误，但没有返回任何内容（undefined）。
英文:
I recommend that you use try...catch to handle possible errors in your request, so your app won't break. Like this:
const fetchData = async () => {
try {
const response = await fetch('https://api.example.com/data');
const jsonData = await response.json();
setData(jsonData);
}
catch (error) {
// If the request returns an error...
setData([]);
}
}
If the error persists, probably your request has no error but is not returning anything (undefined).
答案2
得分: 1
You need to check first data should be defined when component renders.
const MyComponent = () => {
const [data, setData] = useState([]);
useEffect(() => {
fetchData();
}, []);
const fetchData = async () => {
const response = await fetch('https://api.example.com/data');
const jsonData = await response.json();
setData(jsonData);
};
return (
<div>
{data && data.length?.map((item) => (
<div key={item.id}>{item.name}</div>
))}
</div>
);
};
export default MyComponent;
英文:
**You need to check first data should be defined when component renders **
const MyComponent = () => {
const [data, setData] = useState([]);
useEffect(() => {
fetchData();
}, []);
const fetchData = async () => {
const response = await fetch('https://api.example.com/data');
const jsonData = await response.json();
setData(jsonData);
};
return (
<div>
{data && data.length?.map((item) => (
<div key={item.id}>{item.name}</div>
))}
</div>
);
};
export default MyComponent;
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