useEffect 未定义

Question

我无法理解原因，useEffect是存在的，但错误说useEffect未定义 我不明白为什么 useEffect 没有定义，我已经导入了它

import React, { useState, useEffect } from 'react'
import "./MainPage.css"
import { Link } from "react-router-dom";
import { useSelector } from 'react-redux'

 const Bjd = () => {

    const [title, setTitle] = useState('')
    const [desc, setDesc] = useState('')
    const [image, setImage] = useState(undefined)
    const [data, setData] = useState({})


    const role = useSelector((state) => state.auth.role)

    useEffect(() => {
        fetch("http://localhost:3000/request")
            .then(response => response.json())
            .then(data => setData(data))
    }, [])




    
        export default Bjd

我输入了导入的useEffect，但是错误还是一样

Answer 1

看起来你需要从组件本身外部导出组件

import React, { useState, useEffect } from 'react';
import "./MainPage.css";
import { Link } from "react-router-dom";
import { useSelector } from 'react-redux';

const Bjd = () => {
    const [title, setTitle] = useState('');
    const [desc, setDesc] = useState('');
    const [image, setImage] = useState(undefined);
    const [data, setData] = useState({});

    const role = useSelector((state) => state.auth.role);

    useEffect(() => {
        fetch("http://localhost:3000/request")
            .then(response => response.json())
            .then(data => setData(data));
    }, []);

    return (
        <div>
            {/* component */}
        </div>
    );
};

export default Bjd;