{"id":7056,"date":"2023-09-15T17:21:58","date_gmt":"2023-09-15T09:21:58","guid":{"rendered":"https:\/\/i007.vip:15443\/wordpress\/?p=7056"},"modified":"2023-09-15T17:21:58","modified_gmt":"2023-09-15T09:21:58","slug":"react%e4%b9%8busestate%e3%80%81useeffect%e5%8e%9f%e7%90%86%e8%a7%a3%e6%9e%90","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/7056","title":{"rendered":"React\u4e4buseState\u3001useEffect\u539f\u7406\u89e3\u6790"},"content":{"rendered":"
cc from<\/a><\/div>\n
<\/div>\n
\u4e00. useState\u7684\u5b9e\u73b0<\/div>\n
1.1 \u60f0\u6027\u521d\u59cb\u5316state<\/div>\n
1.2 Object.is\u7b97\u6cd5<\/div>\n
\u4e8c. useEffect\u7684\u5b9e\u73b0<\/div>\n
2.1 \u53d8\u91cf\u51b2\u7a81\u95ee\u9898<\/div>\n
2.2 \u53d8\u91cf\u51b2\u7a81\u89e3\u51b3\u65b9\u6848<\/div>\n
\u4e09. \u62d3\u5c55\u5c0f\u77e5\u8bc6<\/div>\n
\u53c2\u8003\u6587\u7ae0\uff1aReact Hook\u7684\u5b9e\u73b0\u539f\u7406\u548c\u6700\u4f73\u5b9e\u8df5<\/div>\n
<\/div>\n
\u4e00. useState\u7684\u5b9e\u73b0<\/div>\n
\u9996\u5148\uff0c\u6211\u4eec\u6765\u770b\u4e00\u4e2a\u7b80\u5355\u7684useState()\u7684\u4f7f\u7528\u6848\u4f8b\uff1a<\/div>\n
<\/div>\n
import ‘.\/App.css’;<\/div>\n
import { useEffect, useState } from ‘react’<\/div>\n
<\/div>\n
function App() {<\/div>\n
\u00a0 const [count, setCount] = useState(0)<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`update—${count}`)<\/div>\n
\u00a0 }, [count])<\/div>\n
<\/div>\n
\u00a0 return (<\/div>\n
\u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => setCount(count + 1)}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${count}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
\u00a0 \u00a0 <\/div><\/div>\n
\u00a0 );<\/div>\n
}<\/div>\n
export default App;<\/div>\n
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\u5206\u6790\uff1a\u6765\u770b\u4e0b\u9762\u8fd9\u884c\u4ee3\u7801\uff1a<\/div>\n
<\/div>\n
const [count, setCount] = useState(0)<\/div>\n
1<\/div>\n
\u53ef\u4ee5\u53d1\u73b0\uff1a<\/div>\n
<\/div>\n
\u8c03\u7528useState()\u51fd\u6570\uff0c\u4f1a\u8fd4\u56de\u4e00\u4e2a\u53d8\u91cf(count)\u4ee5\u53ca\u4e00\u4e2a\u51fd\u6570(setCount)\u3002<\/div>\n
useState()\u51fd\u6570\u4e2d\u53ef\u4ee5\u4f20\u5165\u4e00\u4e2a\u53c2\u6570\uff0c\u4e5f\u5c31\u662f\u8be5\u53d8\u91cf\u7684\u521d\u59cb\u503c\u3002<\/div>\n
\u90a3\u4e48\u6839\u636e\u4e0a\u8ff0\u53d1\u73b0\u76842\u70b9\uff0c\u6211\u4eec\u6765\u81ea\u5b9a\u4e49\u4e00\u4e2a\u51fd\u6570(\u521b\u5efa\u4e2areact\u811a\u624b\u67b6\uff0c\u5728index.js\u6587\u4ef6\u4e2d\u4fee\u6539)\uff1a<\/div>\n
<\/div>\n
import React from “react”;<\/div>\n
import ReactDOM from “react-dom”;<\/div>\n
<\/div>\n
function useState(initVal) {<\/div>\n
\u00a0 let val = initVal;<\/div>\n
\u00a0 function setVal(newVal) {<\/div>\n
\u00a0 \u00a0 val = newVal;<\/div>\n
\u00a0 \u00a0 \/\/ \u4fee\u6539\u53d8\u91cf\u540e\uff0c\u8c03\u7528render\u51fd\u6570\uff0c\u91cd\u65b0\u6e32\u67d3\u9875\u9762<\/div>\n
\u00a0 \u00a0 render();<\/div>\n
\u00a0 }<\/div>\n
\u00a0 return [val, setVal];<\/div>\n
}<\/div>\n
<\/div>\n
function App() {<\/div>\n
\u00a0 const [count, setCount] = useState(0);<\/div>\n
\u00a0 return (<\/div>\n
\u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { console.log(count); setCount(count + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${count}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
\u00a0 \u00a0 <\/div><\/div>\n
\u00a0 )<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u521d\u6b21\u6e32\u67d3\u7528<\/div>\n
render();<\/div>\n
function render() {<\/div>\n
\u00a0 ReactDOM.render(<App \/>, document.getElementById(“root”));<\/div>\n
}<\/div>\n
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\u4f46\u662f\u6548\u679c\u5982\u4e0b\uff1a<\/div>\n
<\/div>\n
<\/div>\n
\u51fa\u73b0\u8fd9\u79cd\u60c5\u51b5\u7684\u539f\u56e0\u5206\u6790\uff1a<\/div>\n
<\/div>\n
\u9996\u5148\uff0c\u53ef\u4ee5\u770b\u5230\u63a7\u5236\u53f0\u4e0a\u6709\u6240\u8f93\u51fa\uff0c\u8bf4\u660e\uff1a\u81ea\u5b9a\u4e49\u7684setState\u51fd\u6570\u6267\u884c\u4e86\u3002<\/div>\n
\u4f46\u7531\u4e8elet val = initVal;\u8fd9\u884c\u4ee3\u7801\u662f\u5728\u51fd\u6570\u5185\u90e8\u88ab\u58f0\u660e\u7684\uff0c\u4e5f\u56e0\u6b64\u6bcf\u6b21\u8c03\u7528useState\u51fd\u6570\u7684\u65f6\u5019\uff0c\u90fd\u4f1a\u91cd\u65b0\u58f0\u660eval\u53d8\u91cf\uff0c\u4ece\u800c\u5bfc\u81f4\u5176\u72b6\u6001\u65e0\u6cd5\u88ab\u4fdd\u5b58\u3002<\/div>\n
\u56e0\u6b64\u6211\u4eec\u5bf9\u4e0a\u8ff0\u4ee3\u7801\u8fdb\u884c\u4e00\u4e2a\u4fee\u6539\uff0c\u5c06val\u53d8\u91cf\u653e\u5230\u5168\u5c40\u4f5c\u7528\u57df\u4e2d\uff1a<\/div>\n
<\/div>\n
\/\/ \u5168\u5c40\u4f5c\u7528\u57df<\/div>\n
let val;<\/div>\n
function useState(initVal) {<\/div>\n
\/\/ \u5224\u65adval\u662f\u5426\u5b58\u5728 \u5b58\u5728\u5c31\u4f7f\u7528<\/div>\n
\u00a0 \u00a0 val = val|| initVal;<\/div>\n
\u00a0 \u00a0 function setVal(newVal) {<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 val = newVal;<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 \/\/ \u4fee\u6539\u53d8\u91cf\u540e\uff0c\u8c03\u7528render\u51fd\u6570\uff0c\u91cd\u65b0\u6e32\u67d3\u9875\u9762<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 render();<\/div>\n
\u00a0 \u00a0 }<\/div>\n
\u00a0 \u00a0 return [val, setVal];<\/div>\n
}<\/div>\n
1<\/div>\n
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\u6b64\u65f6\uff0c\u4ee3\u7801\u4fee\u6539\u540e\u7684\u9875\u9762\u6548\u679c\u624d\u662f\u6b63\u5e38\u7684\uff1a<\/div>\n
<\/div>\n
<\/div>\n
1.1 \u60f0\u6027\u521d\u59cb\u5316state<\/div>\n
\u6211\u4eec\u53ef\u4ee5\u6ce8\u610f\u5230\uff0c\u5728\u4f7f\u7528useState\u7684\u65f6\u5019\uff0c\u5141\u8bb8\u6211\u4eec\u4f20\u5165\u4e00\u4e2a\u53c2\u6570\u4f5c\u4e3a\u8be5\u72b6\u6001\u53d8\u91cf\u7684\u9ed8\u8ba4\u503c\u3002\u6211\u4eec\u5c06\u8fd9\u4e2a\u53c2\u6570\u5148\u547d\u540d\u4e3ainitValue\uff0c\u8be5\u53c2\u6570\u53ea\u4f1a\u5728\u7ec4\u4ef6\u521d\u6b21\u6e32\u67d3\u7684\u65f6\u5019\u8d77\u751f\u6548\uff0c\u5728\u540e\u7eed\u6e32\u67d3\u7684\u65f6\u5019\u5219\u4f1a\u88ab\u5ffd\u7565\u3002<\/div>\n
<\/div>\n
\u540c\u65f6\uff0c\u5018\u82e5\u8fd9\u4e2a\u521d\u59cb\u503c\u9700\u8981\u7ecf\u8fc7\u8ba1\u7b97\u83b7\u5f97\uff0c\u90a3\u4e48\u8fd9\u79cd\u60c5\u51b5\u6211\u4eec\u5927\u81f4\u5206\u4e3a\u8fd9\u4e482\u79cd\u65b9\u5f0f\uff1a<\/div>\n
<\/div>\n
useEffect()\u51fd\u6570\u4e2d\u53bb\u8c03\u7528\u4e00\u4e2a\u4f2a\u4ee3\u7801getUserInfo()\uff0c\u7136\u540e\u901a\u8fc7\u8fd4\u56de\u503c\u53bb\u8c03\u7528setState\u51fd\u6570\u8d4b\u503c\u3002<\/div>\n
\u7b2c\u4e00\u79cd\u4e0d\u5728\u672c\u73af\u8282\u8ba8\u8bba\u8303\u56f4\u5185\uff0c\u90a3\u4e48\u7b2c\u4e8c\u79cd\u5c31\u662f\u7528\u60f0\u6027\u521d\u59cb\u5316state\u7684\u65b9\u5f0f\u3002useState\u4e2d\u4e0d\u4ec5\u53ef\u4ee5\u4f20\u5165\u4e00\u4e2a\u53c2\u6570\u4f5c\u4e3a\u9ed8\u8ba4\u503c\uff0c\u8fd8\u53ef\u4ee5\u4f20\u5165\u4e00\u4e2a\u51fd\u6570\uff0c\u5728\u51fd\u6570\u4e2d\u8ba1\u7b97\u5e76\u8fd4\u56de\u521d\u59cb\u7684state\u5373\u53ef\u3002<\/div>\n
\u4f8b\u5982\uff08\u4f2a\u4ee3\u7801\uff09\uff1a<\/div>\n
<\/div>\n
const [state, setState] = useState(() => {<\/div>\n
\u00a0 const userName= getUserInfo();<\/div>\n
\u00a0 return userName;<\/div>\n
});<\/div>\n
1<\/div>\n
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1.2 Object.is\u7b97\u6cd5<\/div>\n
React\u4e2d\uff0c\u901a\u8fc7Object.is\u7b97\u6cd5\u6765\u6bd4\u8f83\u72b6\u6001\u53d8\u91cf\u7684\u4e0d\u540c\uff0c\u5176\u5224\u522b\u7684\u6807\u51c6\u5982\u4e0b\uff08\u6458\u81ea\u5b98\u7f51\uff09\uff1aObject.is(A,B)\u53ea\u8981\u6ee1\u8db3\u4e0b\u5217\u6761\u4ef6\u4efb\u610f\u4e00\u6761\uff0c\u5c31\u4ee3\u8868\u8fd9\u4e24\u4e2a\u503c\u76f8\u540c\u3002<\/div>\n
<\/div>\n
\u4e24\u4e2a\u90fd undefined.<\/div>\n
\u4e24\u4e2a\u90fd\u662fnull\u3002<\/div>\n
\u4e24\u4e2a\u90fd\u662ftrue\/false\u3002<\/div>\n
\u4e24\u4e2a\u957f\u5ea6\u76f8\u540c\u4e14\u5b57\u7b26\u76f8\u540c\u4e14\u987a\u5e8f\u76f8\u540c\u7684\u5b57\u7b26\u4e32\u3002<\/div>\n
\u4e24\u8005\u90fd\u662f\u540c\u4e00\u4e2a\u5bf9\u8c61\u3002<\/div>\n
\u4e24\u4e2a\u6570\u5b57\u548c\uff1a<\/div>\n
\u4e24\u4e2a\u90fd +0\u3002<\/div>\n
\u4e24\u4e2a\u90fd -0\u3002<\/div>\n
\u4e24\u4e2a\u90fd NaN\u3002<\/div>\n
\u6216\u4e24\u8005\u90fd\u4e0d\u4e3a\u96f6\u4e14\u4e24\u8005\u5747\u4e0dNaN\u76f8\u540c\uff0c\u4e14\u4e24\u8005\u7684\u503c\u76f8\u540c\u3002<\/div>\n
<\/div>\n
Object.is(25, 25);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is(‘foo’, ‘foo’);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is(‘foo’, ‘bar’);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ false<\/div>\n
Object.is(null, null);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is(undefined, undefined);\u00a0 \/\/ true<\/div>\n
Object.is(window, window);\u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is([], []);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ false<\/div>\n
var foo = { a: 1 };<\/div>\n
var bar = { a: 1 };<\/div>\n
Object.is(foo, foo);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is(foo, bar);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ false<\/div>\n
<\/div>\n
\/\/ Case 2: Signed zero<\/div>\n
Object.is(0, -0);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\/\/ false<\/div>\n
Object.is(+0, -0);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ false<\/div>\n
Object.is(-0, -0);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is(0n, -0n);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\/\/ true<\/div>\n
<\/div>\n
\/\/ Case 3: NaN<\/div>\n
Object.is(NaN, 0\/0);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
Object.is(NaN, Number.NaN)\u00a0 \u00a0 \u00a0 \u00a0 \/\/ true<\/div>\n
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\u4e8c. useEffect\u7684\u5b9e\u73b0<\/div>\n
\u6211\u4eec\u77e5\u9053useEffect()\u51fd\u6570\u4f1a\u5728\u7b2c\u4e00\u6b21\u6e32\u67d3\u4e4b\u524d\u8c03\u7528\uff0c\u5e76\u4e14\u6709\u4e24\u4e2a\u53c2\u6570\uff1a<\/div>\n
<\/div>\n
\u53c2\u65701\uff1a\u6267\u884c\u7684\u51fd\u6570\u3002<\/div>\n
\u53c2\u65702\uff1a\u6570\u7ec4\uff08\u53ef\u9009\u53c2\u6570\uff09\uff0cuseEffect()\u51fd\u6570\u6839\u636e\u7b2c\u4e8c\u4e2a\u53c2\u6570\u4e2d\u662f\u5426\u6709\u53d8\u5316\uff0c\u6765\u5224\u65ad\u662f\u5426\u6267\u884c\u7b2c\u4e00\u4e2a\u53c2\u6570\u7684\u51fd\u6570\u3002<\/div>\n
\u4e5f\u56e0\u6b64\uff0c\u6211\u4eec\u5728\u5f00\u53d1\u8fc7\u7a0b\u4e2d\uff0c\u5bf9\u4e8e\u53ea\u5e0c\u671b\u5176\u6267\u884c\u4e00\u6b21\u7684useEffect()\u51fd\u6570\uff0c\u6211\u4eec\u5f80\u5f80\u5199\u5165\u7b2c\u4e8c\u4e2a\u53c2\u6570\u4e3a\u4e00\u4e2a\u7a7a\u6570\u7ec4\uff08\u5426\u5219\u53ef\u80fd\u5f15\u8d77\u65e0\u9650\u6e32\u67d3\u7684BUG\uff09\u3002<\/div>\n
<\/div>\n
\u5b9e\u73b01\uff1auseEffect\u4f20\u5165\u4e00\u4e2a\u51fd\u6570\u53c2\u6570\uff0c\u91cc\u9762\u8c03\u7528\u5373\u53ef\u3002<\/div>\n
<\/div>\n
import React from “react”;<\/div>\n
import ReactDOM from “react-dom”;<\/div>\n
<\/div>\n
let val;<\/div>\n
function useState(initVal) {<\/div>\n
\u00a0 val = val || initVal;<\/div>\n
\u00a0 function setVal(newVal) {<\/div>\n
\u00a0 \u00a0 val = newVal;<\/div>\n
\u00a0 \u00a0 render(); \/\/ \u91cd\u65b0render\u9875\u9762<\/div>\n
\u00a0 }<\/div>\n
\u00a0 return [val, setVal];<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u81ea\u5b9a\u4e49\u7684useEffect<\/div>\n
function useEffect(fn) {<\/div>\n
\u00a0 fn();<\/div>\n
}<\/div>\n
<\/div>\n
function App() {<\/div>\n
\u00a0 const [count, setCount] = useState(0);<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`\u81ea\u5b9a\u4e49useEffect\u8c03\u7528–count\uff1a${count}`);<\/div>\n
\u00a0 });<\/div>\n
\u00a0 return (<\/div>\n
\u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { console.log(count); setCount(count + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${count}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
\u00a0 \u00a0 <\/div><\/div>\n
\u00a0 )<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u521d\u6b21\u6e32\u67d3\u7528<\/div>\n
render();<\/div>\n
function render() {<\/div>\n
\u00a0 ReactDOM.render(<App \/>, document.getElementById(“root”));<\/div>\n
}<\/div>\n
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\u4f46\u662f\u9875\u9762\u6548\u679c\u5982\u4e0b\uff0c\u53ef\u4ee5\u53d1\u73b0\u6bcf\u70b9\u51fb\u4e00\u6b21\u6309\u94ae\uff0c\u5c31\u91cd\u65b0\u6e32\u67d3\u4e00\u6b21\uff0c\u800c\u6bcf\u6b21\u6e32\u67d3\u5219\u8c03\u7528\u4e00\u6b21useEffect()\u51fd\u6570\u3002<\/div>\n
<\/div>\n
\u90a3\u4e48\u518d\u6765\u770b\u770b\u6709\u4e24\u4e2a\u53c2\u6570\u7248\u672c\u7684\u81ea\u5b9a\u4e49useEffect()\u51fd\u6570\uff0c\u8fd9\u4e2a\u51fd\u6570\u9700\u8981\u505a\u5230\uff1a<\/div>\n
<\/div>\n
\u6839\u636e\u7b2c\u4e8c\u4e2a\u53c2\u6570\u6765\u5224\u65ad\u662f\u5426\u6267\u884cuseEffect()\u51fd\u6570\u3002<\/div>\n
let watchArr;<\/div>\n
function useEffect(fn, watch) {<\/div>\n
\u00a0 const hasWactchChange = watchArr<\/div>\n
\u00a0 \u00a0 ? !watch.every((val, i) => val === watchArr[i])<\/div>\n
\u00a0 \u00a0 : true;<\/div>\n
\u00a0 if (hasWactchChange) {<\/div>\n
\u00a0 \u00a0 fn();<\/div>\n
\u00a0 \u00a0 watchArr = watch;<\/div>\n
\u00a0 }<\/div>\n
}<\/div>\n
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\u5b8c\u6574\u6848\u4f8b\u5982\u4e0b\uff08index.js\u6587\u4ef6\uff09\uff1a<\/div>\n
<\/div>\n
import React from “react”;<\/div>\n
import ReactDOM from “react-dom”;<\/div>\n
<\/div>\n
let val;<\/div>\n
function useState(initVal) {<\/div>\n
\u00a0 val = val || initVal;<\/div>\n
\u00a0 function setVal(newVal) {<\/div>\n
\u00a0 \u00a0 val = newVal;<\/div>\n
\u00a0 \u00a0 render(); \/\/ \u91cd\u65b0render\u9875\u9762<\/div>\n
\u00a0 }<\/div>\n
\u00a0 return [val, setVal];<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u81ea\u5b9a\u4e49\u7684useEffect<\/div>\n
let watchArr;<\/div>\n
function useEffect(fn, watch) {<\/div>\n
\u00a0 const hasWactchChange = watchArr<\/div>\n
\u00a0 \u00a0 ? !watch.every((val, i) => val === watchArr[i])<\/div>\n
\u00a0 \u00a0 : true;<\/div>\n
\u00a0 if (hasWactchChange) {<\/div>\n
\u00a0 \u00a0 fn();<\/div>\n
\u00a0 \u00a0 watchArr = watch;<\/div>\n
\u00a0 }<\/div>\n
}<\/div>\n
<\/div>\n
function App() {<\/div>\n
\u00a0 const [count, setCount] = useState(0);<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`\u81ea\u5b9a\u4e49useEffect\u8c03\u7528–count\uff1a${count}`);<\/div>\n
\u00a0 }, []);<\/div>\n
<\/div>\n
\u00a0 return (<\/div>\n
\u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { setCount(count + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${count}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
\u00a0 \u00a0 <\/div><\/div>\n
\u00a0 )<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u521d\u6b21\u6e32\u67d3\u7528<\/div>\n
render();<\/div>\n
function render() {<\/div>\n
\u00a0 ReactDOM.render(<App \/>, document.getElementById(“root”));<\/div>\n
}<\/div>\n
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\u9875\u9762\u6548\u679c\u5982\u4e0b\uff1a\u53ef\u4ee5\u89c1\u5230\uff0cuseEffect()\u51fd\u6570\u5c31\u6267\u884c\u4e86\u4e00\u6b21\uff0c\u56e0\u4e3a\u7b2c\u4e8c\u4e2a\u53c2\u6570\u4e2d\u6211\u4eec\u4f20\u5165\u4e86\u4e00\u4e2a\u7a7a\u6570\u7ec4\u3002<\/div>\n
<\/div>\n
<\/div>\n
2.1 \u53d8\u91cf\u51b2\u7a81\u95ee\u9898<\/div>\n
\u5728\u4e0a\u9762\uff0c\u6211\u4eec\u521d\u6b65\u5b9e\u73b0\u4e86useState\u548cuseEffect\u51fd\u6570\uff0c\u5e76\u6210\u529f\u8c03\u7528\uff0c\u4f46\u662f\u4e0a\u8ff0\u6848\u4f8b\u90fd\u662f\u5728\u4e00\u4e2a\u53d8\u91cf\u7684\u60c5\u51b5\u4e0b\u53d1\u751f\u7684\uff0c\u90a3\u4e48\u5018\u82e5\u6709\u4e24\u4e2a\u53d8\u91cf\u7684\u60c5\u51b5\u4e0b\uff0c\u4f9d\u65e7\u91c7\u7528\u4e0a\u8ff0\u7684\u81ea\u5b9a\u4e49\u4ee3\u7801\uff0c\u4f1a\u53d1\u751f\u4ec0\u4e48\uff1f<\/div>\n
<\/div>\n
\u6848\u4f8b\u5982\u4e0b\uff1a<\/div>\n
<\/div>\n
import React from “react”;<\/div>\n
import ReactDOM from “react-dom”;<\/div>\n
<\/div>\n
let val;<\/div>\n
function useState(initVal) {<\/div>\n
\u00a0 val = val || initVal;<\/div>\n
\u00a0 function setVal(newVal) {<\/div>\n
\u00a0 \u00a0 val = newVal;<\/div>\n
\u00a0 \u00a0 render(); \/\/ \u91cd\u65b0render\u9875\u9762<\/div>\n
\u00a0 }<\/div>\n
\u00a0 return [val, setVal];<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u81ea\u5b9a\u4e49\u7684useEffect<\/div>\n
let watchArr;<\/div>\n
function useEffect(fn, watch) {<\/div>\n
\u00a0 const hasWactchChange = watchArr<\/div>\n
\u00a0 \u00a0 ? !watch.every((val, i) => val === watchArr[i])<\/div>\n
\u00a0 \u00a0 : true;<\/div>\n
\u00a0 if (hasWactchChange) {<\/div>\n
\u00a0 \u00a0 fn();<\/div>\n
\u00a0 \u00a0 watchArr = watch;<\/div>\n
\u00a0 }<\/div>\n
}<\/div>\n
<\/div>\n
function App() {<\/div>\n
\u00a0 const [count, setCount] = useState(0);<\/div>\n
\u00a0 const [data, setData] = useState(0);<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`\u81ea\u5b9a\u4e49useEffect\u8c03\u7528–count\uff1a${count}`);<\/div>\n
\u00a0 }, [count]);<\/div>\n
<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`\u81ea\u5b9a\u4e49useEffect\u8c03\u7528–data\uff1a${data}`);<\/div>\n
\u00a0 }, [data]);<\/div>\n
<\/div>\n
\u00a0 return (<\/div>\n
\u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { setCount(count + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u6309\u94ae1\uff1a\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${count}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
<\/div>\n
\u00a0 \u00a0 \u00a0 <hr \/><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { setData(data + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u6309\u94ae2\uff1a\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${data}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
\u00a0 \u00a0 <\/div><\/div>\n
\u00a0 )<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u521d\u6b21\u6e32\u67d3\u7528<\/div>\n
render();<\/div>\n
function render() {<\/div>\n
\u00a0 ReactDOM.render(<App \/>, document.getElementById(“root”));<\/div>\n
}<\/div>\n
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\u9875\u9762\u6548\u679c\u5982\u4e0b\uff1a<\/div>\n
<\/div>\n
<\/div>\n
\u539f\u56e0\u5206\u6790\uff1a\u4ee5useState\u4e3a\u4f8b\uff1a<\/div>\n
<\/div>\n
\u6240\u6709\u8c03\u7528useState\u65b9\u6cd5\u7684\u5730\u65b9\uff0c\u90fd\u4f1a\u5171\u4eab\u4e00\u4e2a\u5168\u5c40\u53d8\u91cfval\u3002<\/div>\n
\u56e0\u6b64\u5728\u7ec4\u4ef6\u4e2d\u591a\u6b21\u8c03\u7528\uff0c\u5c31\u4f1a\u5f15\u8d77\u53d8\u91cf\u51b2\u7a81\u95ee\u9898\u3002<\/div>\n
2.2 \u53d8\u91cf\u51b2\u7a81\u89e3\u51b3\u65b9\u6848<\/div>\n
\u4ee3\u7801\u6539\u8fdb\uff1a<\/div>\n
<\/div>\n
\u901a\u8fc7\u4e00\u4e2a\u5168\u5c40\u7684\u6570\u7ec4\u6765\u7ef4\u62a4\u53d8\u91cf\u3002<\/div>\n
\u901a\u8fc7\u4e00\u4e2a\u5168\u5c40\u7684\u4e0b\u6807\u7528\u6765\u5b9a\u4f4d\u5bf9\u5e94\u7684\u72b6\u6001\u53d8\u91cf\u5b58\u50a8\u7684\u4f4d\u7f6e\u3002<\/div>\n
\u4ee3\u7801\u5982\u4e0b\uff1a<\/div>\n
<\/div>\n
import React from “react”;<\/div>\n
import ReactDOM from “react-dom”;<\/div>\n
<\/div>\n
let memoizedState = [];<\/div>\n
let currentIndex = 0;<\/div>\n
<\/div>\n
function useState(initVal) {<\/div>\n
\u00a0 memoizedState[currentIndex] = memoizedState[currentIndex] || initVal;<\/div>\n
\u00a0 const cursor = currentIndex;<\/div>\n
\u00a0 function setVal(newVal) {<\/div>\n
\u00a0 \u00a0 memoizedState[cursor] = newVal;<\/div>\n
\u00a0 \u00a0 render();<\/div>\n
\u00a0 }<\/div>\n
\u00a0 \/\/ \u8fd4\u56destate \u7136\u540e currentIndex+1<\/div>\n
\u00a0 return [memoizedState[currentIndex++], setVal];<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u81ea\u5b9a\u4e49\u7684useEffect<\/div>\n
function useEffect(fn, watch) {<\/div>\n
\u00a0 const hasWatchChange = memoizedState[currentIndex]<\/div>\n
\u00a0 \u00a0 ? !watch.every((val, i) => val === memoizedState[currentIndex][i])<\/div>\n
\u00a0 \u00a0 : true;<\/div>\n
\u00a0 if (hasWatchChange) {<\/div>\n
\u00a0 \u00a0 fn();<\/div>\n
\u00a0 \u00a0 memoizedState[currentIndex] = watch;<\/div>\n
\u00a0 \u00a0 currentIndex++; \/\/ \u7d2f\u52a0 currentIndex<\/div>\n
\u00a0 }<\/div>\n
}<\/div>\n
<\/div>\n
function App() {<\/div>\n
\u00a0 const [count, setCount] = useState(0);<\/div>\n
\u00a0 const [data, setData] = useState(0);<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`\u81ea\u5b9a\u4e49useEffect\u8c03\u7528–count\uff1a${count}`);<\/div>\n
\u00a0 }, [count]);<\/div>\n
<\/div>\n
\u00a0 useEffect(() => {<\/div>\n
\u00a0 \u00a0 console.log(`\u81ea\u5b9a\u4e49useEffect\u8c03\u7528–data\uff1a${data}`);<\/div>\n
\u00a0 }, [data]);<\/div>\n
<\/div>\n
\u00a0 return (<\/div>\n
\u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { setCount(count + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u6309\u94ae1\uff1a\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${count}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
<\/div>\n
\u00a0 \u00a0 \u00a0 <hr \/><\/div>\n
\u00a0 \u00a0 \u00a0 <button onClick={() => { setData(data + 1); }}><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 {`\u6309\u94ae2\uff1a\u5f53\u524d\u70b9\u51fb\u6b21\u6570\uff1a${data}`}<\/div>\n
\u00a0 \u00a0 \u00a0 <\/button><\/div>\n
\u00a0 \u00a0 <\/div><\/div>\n
\u00a0 )<\/div>\n
}<\/div>\n
<\/div>\n
\/\/ \u521d\u6b21\u6e32\u67d3\u7528<\/div>\n
render();<\/div>\n
function render() {<\/div>\n
\u00a0 console.log(memoizedState); \/\/ \u6267\u884chook\u540e \u6570\u7ec4\u7684\u53d8\u5316<\/div>\n
\u00a0 currentIndex = 0; \/\/ \u91cd\u65b0render\u65f6\u9700\u8981\u8bbe\u7f6e\u4e3a 0<\/div>\n
\u00a0 ReactDOM.render(<App \/>, document.getElementById(“root”));<\/div>\n
}<\/div>\n
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\u9875\u9762\u6548\u679c\u5982\u4e0b\uff1a<\/div>\n
<\/div>\n
\u4ece\u4e0a\u8ff0\u4ee3\u7801\u4e2d\uff0c\u6211\u4eec\u53ef\u4ee5\u53d1\u73b0\u6bcf\u6b21\u8c03\u7528render()\u51fd\u6570\uff0c\u90fd\u8981\u5c06\u5bf9\u5e94\u7684\u5168\u5c40\u4e0b\u6807\u91cd\u7f6e\u4e3a0\uff0c\u8fd9\u4e2a\u64cd\u4f5c\u6211\u521a\u5f00\u59cb\u770b\u5230\u5c31\u89c9\u5f97\u532a\u5937\u6240\u601d\uff0c\u60f3\u4e86\u534a\u5929\u6211\u624d\u660e\u767d\u662f\u4e3a\u4ec0\u4e48\uff1a<\/div>\n
<\/div>\n
\u56e0\u4e3a\u6211\u4eec\u662f\u6839\u636eHook\u7684\u8c03\u7528\u987a\u5e8f\uff0c\u6765\u4f9d\u6b21\u5c06\u53d8\u91cf\u5b58\u50a8\u5728\u6570\u7ec4\u4e2d\u7684\u3002<\/div>\n
\u800c\u6211\u4eecuseEffect\u51fd\u6570\u7684\u7b2c\u4e8c\u4e2a\u53c2\u6570\u662f\u6570\u7ec4\u7684\u539f\u56e0\uff0c\u4e5f\u662f\u56e0\u4e3a\u6211\u4eec\u53d8\u91cf\u7684\u5b58\u50a8\u4e5f\u662f\u4ee5\u6570\u7ec4\u5f62\u5f0f\u6765\u5b58\u5728\u3002<\/div>\n
\u5907\u6ce8\uff1a<\/div>\n
<\/div>\n
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<\/div>\n
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<\/div>\n
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\u4e09. \u62d3\u5c55\u5c0f\u77e5\u8bc6<\/div>\n
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<\/div>\n
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\u4f2a\u4ee3\u7801\u5982\u4e0b\uff1a<\/div>\n
<\/div>\n
class Demo extends Component{<\/div>\n
\u00a0 \u00a0 render() {<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 return<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 <Button onClick={ () => { console.log(‘Hello World\uff01\uff01’); }}\u00a0 \/><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 <\/div>;<\/div>\n
\u00a0 \u00a0 }<\/div>\n
}<\/div>\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n
8<\/div>\n
\u56e0\u6b64\u6211\u4eec\u5728\u7c7b\u5f0f\u7ec4\u4ef6\u5f00\u53d1\u8fc7\u7a0b\u4e2d\uff0c\u5f80\u5f80\u4f1a\u8fd9\u4e48\u6539\u5199\u4ee3\u7801\uff0c\u6765\u907f\u514d\u6027\u80fd\u6d6a\u8d39\u95ee\u9898\uff1a<\/div>\n
<\/div>\n
class Demo extends Component{<\/div>\n
\u00a0 \u00a0 constructor(){<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 super();<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 this.buttonClick = this.buttonClick.bind(this);<\/div>\n
\u00a0 \u00a0 }<\/div>\n
\u00a0 \u00a0 render() {<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 return<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 <Button onClick={ this.buttonClick }\u00a0 \/><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 <\/div>;<\/div>\n
\u00a0 \u00a0 }<\/div>\n
}<\/div>\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n
8<\/div>\n
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<\/div>\n
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<\/div>\n
function Demo(){<\/div>\n
\u00a0 \u00a0 const buttonClick = useCallback(() => {<\/div>\n
\u00a0 \u00a0 console.log(‘Hello World\uff01\uff01’)<\/div>\n
\u00a0 \u00a0 },[])<\/div>\n
\u00a0 \u00a0 return(<\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 <div><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 <Button onClick={ buttonClick }\u00a0 \/><\/div>\n
\u00a0 \u00a0 \u00a0 \u00a0 <\/div><\/div>\n
\u00a0 \u00a0 )<\/div>\n
}<\/div>\n
1<\/div>\n
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5<\/div>\n
6<\/div>\n
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10<\/div>\n
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