React-hooks

useEffect

UseEffect defaults to the DidMount and Didupdate life cycles
UseEffect If the second parameter is set to [], useEffect is executed only once by default, equivalent to DidMount
The Didupdate life cycle can be simulated by setting the values to listen for changes in the array of the second parameter
Return should function, the content of the function is equivalent to WillUnMount life cycle, in which to execute some, clear timer, clear custom

Note that useEffect emulates both DidMount and Didupdate when the second parameter is not set

When the value of the page changes, an update is triggered, and the content of the function returned WillUnMount. In this case, the value retrieved is the same as the last value because of the nature of the closure

const TestFn = () = > {
    const [age, setAge] = useState(22)

    useEffect(() = > {
        console.log('execution useEffect', age)
        return () = > {
            console.log('Simulated component Destruction', age)
        }
    })

    const handleClick = () = > {
        setAge(age+3)}return (
        <Fragment>
            <div>{age}</div>
            <button onClick={handleClick}>Click on the</button>
        </Fragment>)}export default TestFn
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memo, useMemo, useCallback

It is mainly used for performance optimization
When the value of the parent component changes, the child component is also re-rendered, resulting in unnecessary performance waste
Operation method, used by subcomponentsmemoThe function wrap returns, and the parent listens for any value changes to the child before rendering the child
There’s a function to pass inuseCallback, pass the value, useuseMemoThe second argument to useCallback is an empty array by default
useCallbackThe parent component passes the function past to the child component. By default, the function past is passeduseMemoAnd the Memo subcomponents will still be re-rendered, so useuseCallbackTo keep the child components from rerendering,
The memo defaults to shallow comparisons, so when the parent component passes a reference type (object, array) to the child component, the child component will still be rerendered, so useuseMemoThe second parameter determines which values change before re-rendering

// The default is shallow comparisons like react. # PureComponent
import React, { useState, memo, useMemo, useCallback } from 'react'

const Child = memo(({userInfo}) = > {
    console.log(99)
    return (
        <div>
            Child
            {userInfo.age}
        </div>)})const TestUseMemo = () = > {
    const [count, setCount] = useState(0)
    const [age, setAge] = useState(1)

    const onClick = () = > {
        setCount(count + 1)}const changeChildVal = () = > {
        setAge(age + 1)}const handleClick = useCallback(() = > {
        console.log('handleClick')}, [])const userInfo = useMemo(() = > {
        return {
            age, 
            city: 'chengdu'
        }
    }, [age])


    return (
        <div>
            <div>{count}</div>
            <div>{age}</div>
            <button onClick={onClick}>Click on the</button>
            <button onClick={changeChildVal}>Click on the 2</button>
            <Child handleClick={handleClick} userInfo={userInfo} />
        </div>)}export default TestUseMemo
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Hooks usage specification

Use only in react function components and custom hooks, not elsewhere
It can only be used for top-level code, not for loop, judgment
eslint-plugin-react-hooks

slot

The default slot

<MainFn testMainClick={testMainClick} >
    <div>I'm the default slot</div>
</MainFn>
/ / use
const MainFn = ({children, testMainClick}) = > {
  const handleMain = () = > {
    testMainClick('AAA')}return (
    <div>
      <button onClick={handleMain}>MainFn</button>
      <div>{children // Render children directly to the default slot, default is a JSX, code snippet}</div>
    </div>)}Copy the code

Named slot, and scope slot

A named slot is equivalent to passing in an object, and the key of the object is equivalent to the name of the slot
The scope slot is also passing in an object, each of which corresponds to the value of the key, and passing in a function. The reason for passing in a function is to pass the argument back to the function where the child component uses the slot
JSX and React are written the same in VUe3, except when slots are used for child components
The default slot is ctx.slots.default(). The default slot for react is props. Children
Vue3 gets the named slot and the scope slot ctx.slot.slot1 (666),react :props.children.slot1()

//react
const TestChild = () = > {
  const testMainClick = (val) = > {
    console.log('Get the value passed by the child component', val)
  }

  return (
    <div>
      TestChild
      <MainFn testMainClick={testMainClick} >
        {
          {
            test1(val) {
              console.log('slotAAA', val)
              return <>
                <div>test1__slot</div>
                <div>{val}</div>
              </>}}}</MainFn>
    </div>
  )
}
/ / child component
const MainFn = ({children, testMainClick}) = > {
  const { test1 } = children

  console.log('children', children)

  const handleMain = () = > {
    testMainClick('AAA')}return (
    <div>
      <button onClick={handleMain}>MainFn</button>
      <div>{test1(' pass value back ')}</div>
    </div>)}Copy the code

The use of slots in VUE3

/* Function components with React mode in VUe3 are not responsive */
const TestChild = (props) = > {
  console.log('props', props)
  const data = reactive({ city: 'chongqing' })

  const handleChild = () = > {
    data.city = 'chengdu'
    console.log('handleChild', data)
  }

  return (
    <div>
      <div>{data.city}</div>
      <div>TestChild</div>
      <button onClick={handleChild}>change</button>
    </div>)}/* Functional components in the setup format are reactive */
const TestChild2 = {
  props: {
    city: String
  },
  setup(props, ctx) {
    console.log('propssetup', props, ctx)
    const data = reactive({ city: 'Beijing' })

    const handleChild = () = > {
      data.city = 'Shanghai'
      console.log('handleChild', data)
    }

    return () = > {
      return (
        <div>
          <div>{data.city}</div>
          <div>TestChild2</div>
          <button onClick={handleChild}>change</button>
          <div>{ctx.slots.default(22)}</div>
          <div>{ctx.slots.slot1(666)}</div>
        </div>)}}}// The vuejsx neutron component wants to pass parameters to the parent component, via props.fn()
// If the template method is used, you need to define emits
/ / way
<TestChild
name="AA"
    v-slots={{
        default(val) {
            return <div>TestChildAAA{val}</div>
        },
        slot1(val) {
            return <div>TestChildAAA{val}</div>}}} >2 / / way
<TestChild>
  {{
      default(val) {
            return <div>TestChildAAA{val}</div>
        },
        slot1(val) {
            return <div>TestChildAAA{val}</div>}}}</TestChild>
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react-dom

createPortalthroughcreatePortalThe implementation inserts elements into nodes and performs better than the native method

import ReactDOM from 'react-dom'
ReactDOM.createPortal(
    <div className="modal">{this.props.children}</div>.document.body / / the DOM node
)
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prop-types

prop-typesImplement type checking for props

import PropTypes from 'prop-types'

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syntheticEvent

React events are events that react encapsulates.
React16 event bound to document
The REact17 event is bound to the root component, which makes it easier to have multiple React components, such as a micro front end

The controlled components

It is equivalent to bidirectional data binding
The value in the input is changed by data
OnChange to control input

Uncontrolled component

    <input defaultValue={this.state.name} ref={this.inputRef} />
    
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When uploading files, you must use uncontrolled components

setState

Immutable values, when do you modify them, when do you append them, not in advance
It may be an asynchronous update
It may be merged
Although methods like array push can still render successfully, their values are the same throughout the shouldeComponentUpdate lifecycle, so comparisons can’t be judged

    //nextProps, modified props
    // Change the current state value
    // Compare this.state with nextState and props with nextProps
    // Return true if you want to rerender, false otherwise
    shouldComponentUpdate(nextProps, nextState) {
        console.log('nextProps'.this.state)
        console.log('shouldComponentUpdate', nextProps, nextState)
        return true
    }
    this.inputRef = createRef()
    <input type='file' ref={this.inputRef} />
    console.log('ref'.this.inputRef.current.files)
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immutable

New data structures are generally implemented through the IMmutable library, rather than using depth comparisons, object

The original HTML

const rawHtml = ' Rich text content < I > italic 
        bold '
const rawHtmlData = {
    __html: rawHtml // Note that it must be in this format
}
const rawHtmlElem = <div>
    <p dangerouslySetInnerHTML={rawHtmlData}></p>
    <p>{rawHtml}</p>
</div>
return rawHtmlElem
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Equivalent to nextTick of VUE

const useSyncCallback = callback= > {
    const [proxyState, setProxyState] = useState({ current: false })

    useEffect(() = > {
        if (proxyState.current === true) setProxyState({ current: false })
    }, [proxyState])

    useEffect(() = > {
        proxyState.current && callback()
    })

    return useCallback(() = > {
        setProxyState({ current: true })
    }, [proxyState])
}
const onClick = () = > {
    setCount(count + 1)
    nextTick()  // Get the latest data after execution
}
const nextTick = useSyncCallback(() = > {
    console.log('After change', count)
})
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HOC high-level components

import React from 'react'

// Higher-order components
const withMouse = (Component) = > {
    class withMouseComponent extends React.Component {
        constructor(props) {
            super(props)
            this.state = { x: 0.y: 0 }
        }
  
        handleMouseMove = (event) = > {
            this.setState({
                x: event.clientX,
                y: event.clientY
            })
        }
  
        render() {
            return (
                <div style={{ height: '500px'}}onMouseMove={this.handleMouseMove}>{/* 1. Pass through all props 2.<Component {. this.props} mouse={this.state}/>
                </div>)}}return withMouseComponent
}

const App = (props) = > {
    const a = props.a
    const { x, y } = props.mouse // Receive mouse attributes
    return (
        <div style={{ height: '500px' }}>
            <h1>The mouse position is ({x}, {y})</h1>
            <p>{a}</p>
        </div>)}export default withMouse(App) // Return the higher-order function
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renderProps

import React from 'react'
import PropTypes from 'prop-types'

class Mouse extends React.Component {
    constructor(props) {
        super(props)
        this.state = { x: 0.y: 0 }
    }
  
    handleMouseMove = (event) = > {
      this.setState({
        x: event.clientX,
        y: event.clientY
      })
    }
  
    render() {
      return (
        <div style={{ height: '500px'}}onMouseMove={this.handleMouseMove}>{/* Pass the current state to render(render is a function component) */} {this.props. Render (this.state)}</div>
      )
    }
}
Mouse.propTypes = {
    render: PropTypes.func.isRequired // You must receive a render attribute, which is a function
}

const App = (props) = > (
    <div style={{ height: '500px' }}>
        <p>{props.a}</p>
        <Mouse render={/ *renderIs a function component */ ({x.y}) = > <h1>The mouse position is ({x}, {y})</h1>} / ></div>
)

/** * that is, the Mouse component is defined with only the ability to get x and y. * As for how Mouse components are rendered, the App tells Mouse through Render Prop. * /

export default App

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forwardRef

    // Function components can be passed to ref, or higher order components
    forwardRef((props, ref) = > {})
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react-router-dom

// withRouter can be used to get props. Location, props. Match.params
// This can also be done using hooks provided, useParams,useLocation
//BrowserRouter Specifies the h5 route
// HashRouter Hash mode
UseHistory props.history.push(' /article/${res.id} ')
// props.history.push(`/? page=1&keyword=${keyword}`)
<BrowserRouter>
    // Slots can also be used
    <Route path='/testRouter' component={TestRouter}></Route>
    <Route path='/ClassRouter/:age' component={ClassRouter}></Route>
</BrowserRouter>
// Exact matches only when exact matches. In nested routes, two-level routes can be used but one-level routes cannot be used
//NavLink has an active activeClassName
//Route can be rendered in three ways: by slot, by render, by Component
// The general nested routine is to use a slot or render, render can make the subcomponent get props,
<Route path='/Home' render={(props)= >
    <div>// Let home get props<Home {. props} / >
        <Route path='/Home/Child1' exact component={Child1} />
        <Route path='/Home/Child2' exact component={Child2} />
    </div>} >Copy the code

React is based on the concept of immutable values, and Redux is also immutable values

Hooks are also mutable values

redux

Three packages need to be importedredux.redux-thunk.react-redux

reduxProvides some methods to inject store, and middleware load functions
react-reduxComponents and methods that are primarily used to get state and Dispatch, and Provide
redux-thunkA middleware that handles asynchrony. To handle asynchrony, this middleware must be added

#### Sample code

import * as redux from 'redux'
import thunk from 'redux-thunk'

import * as reactRedux from 'react-redux'
import * as reduxThunk from 'redux-thunk'



console.log('redux', redux)
console.log('reactRedux', reactRedux)
console.log('reduxThunk', reduxThunk)


const { createStore, applyMiddleware } = redux

const defaultState = {
    name: 'Joe'.city: 'chengdu'.age: 22.list: {
        yy: 32}}const promiseFn = (query) = > {
    return new Promise((resolve, reject) = > {
        setTimeout(() = > {
            resolve('Execute in one second' + query)
        }, 1000); })}/* Synchronization */
export const getName = (list) = > {
    // Usually return directly, but in order to get the value in the returned function, use the asynchronous method, which can return a value
    // return {
    // type: 'NAME_ACTION',
    // payload: list
    // }
    return (dispatch) = > {
        dispatch({
            type: 'NAME_ACTION'.payload: list
        })
        return list
    }
}

/* Asynchronous processing */
export const getAsyncName = (list) = > {
    return (dispatch) = > {
        return promiseFn(list).then(res= > {
            dispatch({
                type: 'NAME_ACTION'.payload: res
            })
            return res
        })
    }
}

const reducer = (state = defaultState, action) = > {
    // console.log(' test action', action)
    if(action.type === 'NAME_ACTION') {
        // state.age = action.payloadstate.list.yy = action.payload state = {... state} }return state
}

const store = createStore(reducer, applyMiddleware(thunk))

import React from 'react'
import * as reactRedux from 'react-redux'
import { getName, getAsyncName } from '.. /.. /.. /store/index'


// console.log('; reactRedux', reactRedux, getName)

const { useDispatch, useSelector } = reactRedux



const Child1 = (props) = > {
    const disptch = useDispatch()

    const age = useSelector(state= > {
        // console.log(' get ', state.list.yy)
        // return state.age
        return state.list.yy
    })

    const handleBtn1 = () = > {
        const data = disptch(getName('Synced up, buddy.'))
        console.log('get AAA', data)
    }

    const handleBtn2 = () = > {
        disptch(getAsyncName(883263)).then(res= > {
            console.log('res', res)
        })
        // console.log(' get AAA', age)
    }

    console.log('the Child1 props', props)
    return <div>
        Child1
        <div>AA{age}</div>
        <button onClick={handleBtn1}>Synchronously triggers redux</button>
        <button onClick={handleBtn2}>Asynchronously trigger redux</button>
    </div>
}

export default Child1

export default store

// Inject at the top-level store
<Provider store={store}>
    <App />
</Provider>
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React Install the TS environment

npx create-react-app my-react-ts –typescript

React uses typescript

import React from "react";

interfacetestProps { message? :string
}
// You can use the react. FC abbreviation
const Test: React.FunctionComponent<testProps> = (props) = > {
    return <div>
        {props.message}
    </div>
}

Test.defaultProps = {
    message: 'Hello.'
}

export default Test

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React dynamically adds classes

The installationnpm i classnames

useEffect

memo, useMemo, useCallback

Hooks usage specification

slot

The use of slots in VUE3

react-dom

prop-types

syntheticEvent

The controlled components

Uncontrolled component

setState

immutable

The original HTML

Equivalent to nextTick of VUE

HOC high-level components

renderProps

forwardRef

react-router-dom

React is based on the concept of immutable values, and Redux is also immutable values

redux

React Install the TS environment

React uses typescript

React dynamically adds classes

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