当我尝试连接后端与React时，为什么返回` `Cannot property 'map‘of unfined`？

import React, { useState, useEffect } from 'react';

const MyComponent = () => {
  const [data, setData] = useState([]);

  useEffect(() => {
    fetchData(); // 从后端获取数据的函数
  }, []);

  const fetchData = async () => {
    try {
      const response = await fetch('后端数据接口');
      const jsonData = await response.json();
      setData(jsonData);
    } catch (error) {
      console.log(error);
    }
  };

  return (
    <div>
      {data.length > 0 ? (
        data.map((item) => (
          <div key={item.id}>
            {/* 渲染数据 */}
          </div>
        ))
      ) : (
        <div>
          {/* 数据加载中或者无数据的提示 */}
        </div>
      )}
    </div>
  );
};

export default MyComponent;