标签:count return 函数 hooks React useState count1 const useEffect
1、箭头函数
import React, {useState} from "react";
const App1 = () => {
const [count, setCount] = useState(0);
return (
<div>
<button onClick={event => setCount(count + 1)}>count:{count}</button>
</div>
)
}
export default App1;
2、useState
import React, {useEffect, useRef, useState} from "react";
const App2 = () => {
const [count, addCount] = useState(0);
return (
<div>
<button onClick={event => addCount(count + 1)}>count1:{count}</button>
</div>
)
}
export default App2;
3、useEffect
import React, {useEffect, useState} from "react";
function useCount(initVlue) {
const [count, setCount] = useState(initVlue);
return [count, () => {
setCount(count + 1)
}]
}
function log(count) {
console.log('你已经点击:' + count + '下了')
}
function useInterval(callback, time) {
useEffect(() => {
const i = setInterval(callback, time);
return () => {
clearInterval(i)
}
}, [])
}
const App3 = () => {
const [count1, addCount1] = useCount(0);
const [count2, addCount2] = useCount(0);
const [count3, setCount3] = useState(0);
useInterval(() => {
setCount3(prevState => prevState + 1)
//这个方式只能第一次生效,后面不生效,上面得函数是可以得
//setCount3(count3 + 1)
}, 1000);
//表示起了什么作用,这块表示骑了打印日志的作用,理解成一个描述,而不是一个方法调用
//useEffect(log.bind(count1,[1])); 依赖1次执行的结果,只执行一次
//useEffect(log.bind(count1),[]); 依赖空执行的结果,只执行一次
useEffect(log.bind(null, count1)); //依赖count1执行的结果,每次都执行
return (
<div>
<button onClick={event => addCount1()}>count1:{count1}</button>
<button onClick={event => addCount2()}>count2:{count2}</button>
<button onClick={event => setCount3(count3 + 1)}>count3:{count3}</button>
</div>
)
}
export default App3;
4、useReducer
import React, {useReducer} from "react";
function reducer(state, action) {
switch (action.type) {
case 'add':
return state + 1;
case 'red':
return state - 1;
default :
throw 'erro'
}
}
const App4 = () => {
const [number, dispatcher] = useReducer(reducer, 0)
return (
<div>
<p>your number is {number}</p>
<button onClick={event => dispatcher({type: 'add'})}> +</button>
<button onClick={event => dispatcher({type: 'red'})}> -</button>
</div>
)
}
export default App4;
标签:count,return,函数,hooks,React,useState,count1,const,useEffect 来源: https://blog.csdn.net/yoonerloop/article/details/110261295
本站声明: 1. iCode9 技术分享网(下文简称本站)提供的所有内容,仅供技术学习、探讨和分享; 2. 关于本站的所有留言、评论、转载及引用,纯属内容发起人的个人观点,与本站观点和立场无关; 3. 关于本站的所有言论和文字,纯属内容发起人的个人观点,与本站观点和立场无关; 4. 本站文章均是网友提供,不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属;如您发现该文章侵犯了您的权益,可联系我们第一时间进行删除; 5. 本站为非盈利性的个人网站,所有内容不会用来进行牟利,也不会利用任何形式的广告来间接获益,纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。