等效于使用React挂钩的componentDidUpdate

class MyComponent extends React.Component {
  state = { data: null };

  componentDidMount() {
    this.fetchData();
  }

  componentDidUpdate(prevProps, prevState) {
    if (prevProps.someProp !== this.props.someProp) {
      this.fetchData();
    }
  }

  fetchData = () => {
    // 获取数据的逻辑
  };

  render() {
    return <div>{this.state.data}</div>;
  }
}

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

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

  useEffect(() => {
    const fetchData = async () => {
      // 获取数据的逻辑
      const result = await fetchSomeData(someProp);
      setData(result);
    };

    fetchData();
  }, [someProp]);

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

useEffect(() => {
  setState(prevState => prevState + 1); // 这会导致无限循环
}, []);

useEffect(() => {
  const interval = setInterval(() => {
    setState(prevState => prevState + 1);
  }, 1000);

  return () => clearInterval(interval); // 清理副作用
}, []);

useEffect(() => {
  console.log('Component updated');
}, [someProp]); // 如果 someProp 没有变化，useEffect 不会执行