react hooks基础demo

hooks基础demo

import React,{useState,useEffect,createContext,useContext,useMemo,memo,useRef,PureComponent} from 'react'

const CountText = createContext();

//react hooks写法
/*function Counter(props) {
    const count = useContext(CountText);
    return(
        
{count}
    )
}*/

// Counter函数写法，如果使用ref就必须写成class
/*const Counter = memo(function  Counter(props){
    console.log('counter render');
    return(
        
{props.count}
    )
})*/

class Counter extends PureComponent{
    speak(){
        console.log('speak');
    }
    render(){
        let {props} = this;
        return(
            <h1 onClick={props.clickCounter}>{props.count}</h1>
        )
    }
}


// 自定义hook，命名必须以use开头
function useCount(defaultCount){
    const [myCount,setMyCount] = useState(defaultCount);
    const changeMyCount = ()=>{
        setMyCount(myCount+1)
    }
    useEffect(()=>{
        document.querySelector("#changeMyCount").addEventListener('click',changeMyCount,false)
    },[myCount])
    return [myCount,setMyCount];
}

const Hook = function () {
    const  [myCount,setMyCount] = useCount(0)
    const [count,setCount] = useState(0);
    const [name,setName] = useState('hello world');
    const counterRef = useRef();
    const [size,setSize] = useState({
        width:document.documentElement.clientWidth,
        height:document.documentElement.clientHeight
    })

    const onResize = ()=>{
        setSize({
            width:document.documentElement.clientWidth,
            height:document.documentElement.clientHeight
        })
    }

    const changeCount = ()=>{
        setCount(count+1)
        console.log(count)
    }

    const changeSize = ()=>{
        console.log('size')
    }

    const clickCounter = ()=>{
        console.log(count)
    }

    const getRef = () => {
        //获取Conter组件的speak方法
        counterRef.current.speak()
    }

    useEffect(()=>{
        document.title=count;
    })

    useEffect(() => {
        window.addEventListener('resize',onResize,false);
        return () => {
            window.removeEventListener('resize',onResize,false);
        }
    },[])

    // count改变调用
    useEffect(()=>{
        console.log(count)
    },[count])

    useEffect(()=>{
        document.querySelector("#change").addEventListener('click',changeCount,false)
    },[count])

    useEffect(()=>{
        document.querySelector("#size").addEventListener('click',changeSize,false)

        return(
            document.querySelector("#size").removeEventListener('click',changeSize,false)
        )
    })

    useEffect(()=>{
        document.querySelector("#btn").addEventListener('click',getRef,false)
    },[counterRef])

    const double = useMemo(() => {
        return count*2;
    },[count==3]) //当count==3，这个才有效，这里也可以直接是count

    const half = useMemo(() => {
        return double/2;
    });//可以依赖于上面的useMemo

    return(
        <div>
            <button onClick={()=>{setCount(count+1)}}>{count}</button>
            <button onClick={()=>{setName('你好，react hook')}}>{name}</button>
            <button id='change'>使用useEffect绑定事件</button>
            <button id='btn'>使用useRef获取Counter</button>
            {size.width}*{size.height}

            <br/>
            {count%2==0
                ?(<span id="size">我是偶数</span>)
                :(<span id="size">我是奇数</span>)
                }
{/*            userContext:
            
                
            */}
            <Counter ref={counterRef} count={count} clickCounter={clickCounter}/>
            {double}--{half}
            <br/>
            <button id='changeMyCount'>自定义hook</button>
            <h3>自定义hook:{myCount}</h3>
        </div>
    )
}

export default Hook