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1.useEffect不带第二个参数

// Similar to componentDidMount and componentDidUpdate:  useEffect(() => {    // Update the document title using the browser API    document.title = `You clicked ${count} times`;  });

例子

import React, { useState, useEffect } from 'react';import { Button } from '@alifd/next';export default function Example() {  const [count, setCount] = useState(0);  // Similar to componentDidMount and componentDidUpdate:  // 加载和state更新的时候会触发  useEffect(() => {    console.log(`hook-----${new Date()}`);    console.log(`count ${count} times`);    // Update the document title using the browser API    document.title = `You clicked ${count} times`;  });  return (    
   
      
    
You clicked {count} times
      
     setCount(count + 1)}>Click me    
   
  );}

当组件第一次被加载进来的时候，控制台打印

当每次点击按钮'cclick me',控制台打印