React Hook useState useEffect componentDidMount componentDidUpdate componentWillUnmount问题

import React, { useState } from 'react';

function Example() {
  // 声明一个叫 "count" 的 state 变量
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

class Example extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  render() {
    return (
      <div>
        <p>You clicked {this.state.count} times</p>
        <button onClick={() => this.setState({ count: this.state.count + 1 })}>
          Click me
        </button>
      </div>
    );
  }
}

import React, { useState } from 'react';

function Example() {
  // 声明一个叫 "count" 的 state 变量
  const [
	  count, 　// 在state里面的名字
	  setCount  // 改变这个名字的函数
  ] = useState(
  	0  // 初值count的初值
  );

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => 
      setCount(
      count + 1  //  准备把count该成什么样子
      )}>
        Click me
      </button>
    </div>
  );
}

// 表格loading
  const [loading, setLoading] = useState(true);

  // 表格数据
  const [listData, setListData] = useState({ list: [], total: 0 });

  // 当前页码
  const [current, setCurrent] = useState(0);

  // 搜索数据
  const [searchData, setSearchData] = useState({});

  // 医生职称
  const [jobTitle, setJobTitle] = useState([]);

  // 科室
  const [dept, setDept] = useState([]);

  // 弹窗显隐
  const [visible, setVisible] = useState(false);

  // 弹窗数据
  const [showData, setShowData] = useState({});

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

function Example() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    document.title = `You clicked ${count} times`;
  });

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

useEffect(
  () => { // 我叫A函数
    const subscription = props.source.subscribe();
    return () => {
      subscription.unsubscribe();
    };
  },
  [props.source],
);

useEffect(() => {
    const firstGet = async () => {
      const [z, x, c] = await Promise.all([
        requestZ(),
        requestX(),
        requestZ(),
      ]);
      // 做你想做的事情
    };
    firstGet();
  }, []);

useEffect(() => {
    // Specify how to clean up after this effect:
    return function cleanup() {
      ChatAPI.unsubscribeFromFriendStatus(props.friend.id, handleStatusChange);
    };
  }, []);