未捕获(在promise中) ReferenceError: react组件中未定义数据

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

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

  useEffect(() => {
    let isMounted = true;

    fetchData().then(result => {
      if (isMounted) {
        setData(result);
      }
    }).catch(error => {
      console.error(error);
    });

    return () => {
      isMounted = false;
    };
  }, []);

  // 组件渲染逻辑...

  return (
    <div>{data}</div>
  );
}

function fetchData() {
  return new Promise((resolve, reject) => {
    // 异步操作...
    // 完成后调用 resolve(data) 或 reject(error)
  });
}

export default MyComponent;