importReact,{useEffect}from'react';functionWelcome(props){useEffect(()=>{document.title='加载完成';});return<h1>Hello,{props.name}</h1>;} 上面例子中,useEffect()的参数是一个函数,它就是所要完成的副效应(改变网页标题)。组件加载以后,React 就会执行
functionCounter(){const[count,setCount]=useState(0);useEffect(()=>{setTimeout(()=>{console.log(`You clicked${count}times`);},3000);});return(You clicked{count}timessetCount(count+1)}>Click me);} 结果如下: 在Class 组件中的使用生命周期,代码示例: 代码语言:javascript 代码运行次数:0 运...
import React, { useState, useEffect } from "react"; import ReactDOM from "react-dom"; function App() { const [visible,setVisible]
function HelloWorld() { useEffect(() => { console.log('HelloWorld Mount') return () => { console.log('HelloWorld Unmount') } }, []) return hello world } function App() { const [visible, useVisible] = useState(true) useEffect(() => { console.log('App Mount') }, []) return (...
import React, { useState } from "react"; import ReactDOM from "react-dom"; function App() { const [n, setN] = useState(0); const onClick = () => { setN(n + 1); }; React.useEffect(() => { console.log("App"); return () => { console.log("App挂了"); }; }); retu...
useEffect(function () { console.log("3-生命周期--组件挂载时调用"); //约等价于 componentDidMount //只会在组件挂载时触发 }, []); //4.组件更新/卸载时的生命周期方法 useEffect(function () { return function () { console.log("4-生命周期--组件更新/卸载时调用"); ...
import React, { useEffect, useState } from 'react'; function Timer() { const [time,setTime] = useState(0); useEffect(() => { const timer = setInterval(() => { setTime(time => time + 1); }, 1000); //返回清除函数 return () => { clearInterval(timer); }; }, []); return...
import{ useEffect, useState }from"react" functionSon() { // 1. 渲染时开启一个定时器 useEffect(() =>{ consttimer =setInterval(() =>{ console.log('定时器执行中...') },1000) return() =>{ // 清除副作用(组件卸载时) clearInterval(timer) ...
interfaceReact{// ...useEffect(create:()=>(()=>void)|void,deps:Array<mixed>|void|null):void} 参数 setup:Function 一个定义了功能的函数, 当组件首次渲染的时候会执行, 后续每次依赖发生变化的时候也会被调用, 可选的返回一个清理函数cleanup(如果return非函数会警告), 在每次依赖发生修改, 调用setup之...
function ExampleComponent() { useEffect(() => { // 副作用函数在组件挂载、更新或即将卸载时调用 console.log('Effect is called'); return () => { // 清除副作用,比如取消订阅或清理定时器 console.log('Effect cleanup'); }; }, []); // 第二个参数为空数组表示只在挂载和卸载时执行 ...