useEffect：dom完成渲染后执行
- 不传参数，每次都会执行
传空的依赖[]，只会执行一次
有依赖，依赖项变化会执行
useEffect实现动画效果
import { useEffect, useRef, useState } from "react"const App = () => {const [, setCount] = useState({})const refDiv = useRef()useEffect(() => {console.log('执行useEffect')setTimeout(() => {refDiv.current.style.transform = 'translateX(150px)'refDiv.current.style.transition = 'all .9s'}, 1000)// 清理函数 要显示返回的动画，上面的函数应延迟一段执行// 否则太快回到150px位置，看不到效果return () => {console.log('执行清理函数')refDiv.current.style.transform = 'translateX(0px)'refDiv.current.style.transition = 'all .9s'}})const styleObj = {width: '50px',height: '50px',background: 'skyblue'}return (<><div style={styleObj} ref={refDiv}></div><button onClick={() => setCount({})}>click</button></>)
}
export default App
useLayoutEffect
- 和
componentDidMount和componentDidUpdate调用阶段一致
import { useEffect, useLayoutEffect, useRef, useState } from "react"const App = () => {const [, setCount] = useState({})const refDiv = useRef()useLayoutEffect(() => {console.log('useLayoutEffect渲染前执行')// 若不延迟 在useLayoutEffect看不到移动，而是初始就在150的位置setTimeout(() => {refDiv.current.style.transform = 'translateX(150px)'refDiv.current.style.transition = 'all .9s'}, 1000)return () => {console.log('执行清理函数')refDiv.current.style.transform = 'translateX(0px)'refDiv.current.style.transition = 'all .9s'}})const styleObj = {width: '50px',height: '50px',background: 'skyblue'}return (<><div style={styleObj} ref={refDiv}></div><button onClick={() => setCount({})}>click</button></>)
}
export default App
useDebugValue
- 用于在React开发者工具中显示自定义hook的标签
自定义hook
import { useEffect, useState } from 'react'
// 自定义hook
const useCount = params => {const [count, setCount] = useState(0)useEffect(() => {document.title = `第${count}次点击`})return [count, setCount]
}
const Foo = () => {const [count, setCount] = useCount(0)useEffect(() => {console.log('Foo useEffect')})return (<><h1>{count}</h1><button onClick={() => setCount(count + 1)}>click</button></>)
}
const App = () => {return <Foo />
}
export default App
增加提示效果
