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自定义hook： 用来封装复用的逻辑，，自定义hook是以use开头的普通函数，，将组件中可复用的状态逻辑抽取到自定义的hook中，简化组件代码

常见自定义hook例子：

封装一个简单的计数器

import {useState} from "react";function useCounter(initialValue:number){const [count, setCount] = useState(0)const increment = ()=>setCount(prev=>prev+1)const decrement = ()=>setCount(prev=>prev-1)const reset = ()=>setCount(initialValue)return {count,increment,decrement,reset}
}export default useCounter

封装一个自动监听网页窗口变化的hooks

import {useEffect, useState} from "react";function useWindowSize(){const [size, setSize] = useState({width:window.innerWidth,height:window.innerHeight})useEffect(() => {const handleResize = ()=>{setSize({width: window.innerWidth,height: window.innerHeight})}window.addEventListener("resize",handleResize)return ()=> window.removeEventListener("resize",handleResize)}, []);return size
}export default useWindowSize

封装一个网络请求的hooks,返回请求的状态

import {useEffect, useState} from "react";
import axios from "axios";interface FetchResult<T>{data:T | null,loading:boolean,error: Error | null
}
function useFetch<T = any>(url:string):FetchResult<T>{const [data, setData] = useState<T | null>(null)const [loading, setLoading] = useState(true)const [error, setError] = useState<Error | null>(null)useEffect(() => {const fetchData = async ()=>{try {const response = await axios.get(url)console.log(response)setData(response.data)} catch (e) {setError(e as Error)} finally {setLoading(false)}}fetchData()}, [url]);return {data,loading,error}}export default useFetch

hook设置获取localStorage

import {useState} from "react";function useLocalStorage<T>(key:string,initialValue:T | null){const [storeValue, setStoreValue] = useState(()=>{try {var item = window.localStorage.getItem(key);return item ? JSON.parse(item) : initialValue} catch (e) {console.log(e)return initialValue}})const setValue = (val:T | null)=>{try {setStoreValue(val)if (val){window.localStorage.setItem(key, JSON.stringify(val))}else{window.localStorage.removeItem(key)}} catch (e) {console.log(e)}}return [storeValue,setValue] as const}export default useLocalStorage

调用hook：

import useCounter from "./useCounter";
import useWindowSize from "./useWindowSize";
import useFetch from "./useFetch";
import useLocalStorage from "./useLocalStorage";function CustomHook(){const {count,increment,decrement,reset} = useCounter(10)const {width,height} =useWindowSize()const {data,loading,error} = useFetch("http://localhost:9090/hello")const [token,setToken] = useLocalStorage<String | null>("token",null)if (loading) return <div>loading ....</div>if (error) return  <div>error: {error.message}</div>return (<div><div> {width}</div><div> {height}</div>{count}<button onClick={increment}>increment</button><button onClick={decrement}>decrement</button>{data}<h3> token is :{token}</h3><button onClick={()=>setToken("123")}>123</button></div>)
}export default CustomHook