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;
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论