浅谈React

$程2024-07-11 15:38

forwardRef和useImperativeHandle的联动使用

复制代码

import React, { useImperativeHandle, useRef } from "react"
import { forwardRef } from "react"

const CustomInput = forwardRef((props, ref) => {
    const inputRef = useRef<HTMLInputElement>(null)

    useImperativeHandle(ref, () => ({
        focus: () => {
            inputRef.current?.focus()
        }
    }))
    return <div>
        <input ref={inputRef} />
    </div>
})

export default CustomInput

巧用children

一般用法

父组件：

import React from "react"
import Child from './Child'

const CustomInput = () => {
return <Child>

hello 靓仔

</Child>
}

export default CustomInput

子组件：

import React from "react"

const Child = ({
children
}) => {
return
{children}

}

export default Child
函数用法

父组件：

import React from "react"
import Child from './Child'

const CustomInput = () => {
return <Child>
{(arr)=>

{arr.map((v,idx)=>{
return
{v}

})}

}
</Child>
}

export default CustomInput

子组件：

import React from "react"

const Child = ({
children
}) => {
const arr = [1,2,4,5]
return
{children(arr)}

}

export default Child

useEffect

没有依赖，类似于componentDidMount和componentDidUpdate

import React, { useEffect, useState } from "react"

const Detail = () => {
const [count, setCount] = useState(1)
const [num,setNum] = useState(2)
useEffect(()=>{
console.log(count,'count',num,'num')
})
return

<div onClick={() => setCount(count + 1)}>add count

<div onClick={() => setNum(num + 1)}>add num

count: {count}

num: {num}

}

export default Detail

依赖是个空数组，相当于componentDidMount

import React, { useEffect, useState } from "react"

const Detail = () => {
const [count, setCount] = useState(1)
const [num,setNum] = useState(2)
useEffect(()=>{
console.log(count,'count',num,'num')
},[])
return

<div onClick={() => setCount(count + 1)}>add count

<div onClick={() => setNum(num + 1)}>add num

count: {count}

num: {num}

}

export default Detail

有依赖，componentDidMount和对应依赖的componentDidUpdate

import React, { useEffect, useState } from "react"

const Detail = () => {
const [count, setCount] = useState(1)
const [num,setNum] = useState(2)
useEffect(()=>{
console.log(count,'count',num,'num')
},[num])
return

<div onClick={() => setCount(count + 1)}>add count

<div onClick={() => setNum(num + 1)}>add num

count: {count}

num: {num}

}

export default Detail

useEffect和useLayoutEffect

useEffect在渲染后执行，而useLayouEffect是在渲染之前执行

最典型的例子就是实现一个tooltip组件，在性能比较差的情况下，useEffect会先渲染初始状态再更新，而useLayoutEffect会阻塞UI的更新即不会出现组件闪烁的情况~

阻塞代码：

复制代码

let now = performance.now();
while (performance.now() - now < 100) {
}

useEffect在性能差的情况下会出现以下效果

useContext

依赖注入

复制代码

父级：
export const ThemeContext = createContext({});
const App = ()=>{

return  <ThemeContext.Provider value={{name:"real hot"}}>
        ......
    </ThemeContext.Provider>
}

 子级：
  const context = useContext(ThemeContext)
  console.log(context)

useState的变动

在react管辖下(react17.x.x)

函数形式

状态能够更改多次，只渲染一次

复制代码

const handleCount= ()=>{
  setCount(count=>count+1)
  setCount(count=>count+1)
}

对象形式

多次更改状态会被合并成一次更改，即一次生效其他无效，只渲染一次

复制代码

const handleCount= ()=>{
  setCount(count+1)
  setCount(count+1)
}

在异步任务/原生事件下(react17.x.x)

复制代码

const handleCount= ()=>{
setTimeout(()=>{
  setCount(count=>count+1)
  setCount(count=>count+1)
})
}

版本的演变（React18）

react18之后在异步操作或者react事件中都是批量更新，即多个状态更新合成一次渲染，若需要多次渲染可使用flushsync

复制代码

const handleCount= ()=>{
  flushSync(()=>{
    setCount(count=>count+1)
  })
  flushSync(()=>{
    setCount(count=>count+1)
  })

}

探索生命周期函数

父子组件生命周期执行顺序

挂载：

更新：

卸载：

错误处理

生命周期方法：

getDerivedStateFromError

componentDidCatch

缺点（没办法捕获）：

异步操作
事件处理函数报错

错误边界自己报错

class ErrorBoundary extends React.Component {
constructor(props) {
super(props);
this.state = { hasError: false };
}

复制代码

static getDerivedStateFromError(error) {
  // Update state so the next render will show the fallback UI.
  return { hasError: true };
}

componentDidCatch(error, errorInfo) {
  // You can also log the error to an error reporting service
  logErrorToMyService(error, errorInfo);
}

render() {
  if (this.state.hasError) {
    // You can render any custom fallback UI
    return <h1>Something went wrong.</h1>;
  }

  return this.props.children; 
}

}

实现一个简单的Message

复制代码

import ReactDOM from 'react-dom';
import { Modal } from 'antd';
const ToastFn = () => {
let parent = null;
return {
open: function ({ el, container = document.body }) {
// this.destroy();
parent = document.createElement('div');
document.body.appendChild(parent);
ReactDOM.render(<Modal open onCancel={this.destroy}>{el}</Modal>, parent)
},
destroy: function () {
ReactDOM.unmountComponentAtNode(parent);
},
};
};
const Toast = ToastFn();
export default Toast;

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