React中常用的Hook有哪些

export default class Demo extends Component {
	state = {count:0}
	add = () => {
		this.setState(state => ({count: state.count + 1}))
	}
	render() {
		return (
			<div>
				<h2>当前求和为：{this.state.count}</h2>
				<button onClick={this.add}>点我加1</button>
			</div>
		)
	}
}

export default function Demo() {
	const [count,setCount] = React.useState(0)
	// 其他状态也要用同样的方法
	const [name,setName] = React.useState('Jack')
	function add() {
		// 写法一
		// setCount(count + 1)
		// 写法二
		setCount(count => count + 1)
	}
	return (
		<div>
			<h2>当前求和为：{this.state.count}</h2>
			<button onClick={add}>点我加1</button>
		</div>
	)
}

useEffect(() => { 
    // 在此可以执行任何带副作用操作
    return () => { // 在组件卸载前执行
      // 在此做一些收尾工作, 比如清除定时器/取消订阅等
    }
}, [stateValue]) // 如果指定的是[], 回调函数只会在第一次render()后执行

export default class Demo extends Component {
	state = {count:0}
	add = () => {
		this.setState(state => ({count: state.count + 1}))
	}
	unmount = () => {
		ReactDOM.unmountComponentAtnode(document.getElementById('root'))
	}
	componentDidMount() {
		this.timer = setInterval(() => {
			this.setState(state => ({count:state.count + 1}))
		},1000)
	}
	componentWillUnmount(){
		clearInterval(this.timer)
	}
	render() {
		return (
			<div>
				<h2>当前求和为：{this.state.count}</h2>
				<button onClick={this.add}>点我加1</button>
				<button onClick={this.unmount}>卸载组件</button>
			</div>
		)
	}
}

export default function Demo() {
	const [count,setCount] = React.useState(0)
	React.useEffect(() => {
		let timer = setInterval(() => {
			setCount(count=> count + 1)
		},1000)
		return () => {
			clearInterval(timer)
		}
	},[])
	function add() {
		setCount(count => count + 1)
	}
	function unmount() {
		ReactDOM.unmountComponentAtNode(document.getElementById('root'))
	}
	return (
		<div>
			<h2>当前求和为：{this.state.count}</h2>
			<button onClick={add}>点我加1</button>
			<button onClick={unmount}>卸载组件</button>
		</div>
	)
}

export default class Demo extends Component {
	myRef = React.createRef()
	show = ()=>{
		alert(this.myRef.current.value)
	}
	render() {
		return (
			<div>
				<input type="text" ref={this.myRef}/>
				<button onClick={this.show }>点击提示数据</button>
			</div>
		)
	}
}

export default class Demo extends Component {
	const myRef = React.useRef()
	function show() {
		alert(myRef.current.value)
	}
	render() {
		return (
			<div>
				<input type="text" ref={myRef}/>
				<button onClick={show }>点击提示数据</button>
			</div>
		)
	}
}