使用useMemo优化性能

使用useMemo优化性能：

import React, { Suspense, useMemo } from 'react'
import { Switch, Route } from 'react-router-dom'
import { connect } from 'react-redux'
import Loading from '../../../components/light/Loading'
import Header from './Header'
import Nav from './Nav'

function List(props) {
  const { router } = props
 

  // 只有router变化时才会重新渲染listDom，useMemo函数可以起到性能优化的作用
  const listDom = useMemo(() => {
    const listDom = []
    const listRender = (arr) => {
      arr.forEach((item) => {
        if (item.children) {
          listRender(item.children)
        } else {
          listDom.push(
            <Route
              key={item.path}
              path={item.path}
              component={item.component}
            ></Route>
          )
        }
      })
    }
    listRender(router.toJS())
    return listDom
  }, [router])

  return (
    <div className="m-list">
      <Header></Header>
      <div className="m-list-info">
        <Nav></Nav>
        <Suspense fallback={<Loading isLazyLoading={true}></Loading>}>
          <Switch>{listDom}</Switch>
        </Suspense>
      </div>
    </div>
  )
}

const mapStateToProps = (state) => {
  return {
    router: state.getIn(['light', 'router']),
    theme: state.getIn(['light', 'theme']),
  }
}

const mapDispatchToProps = (dispatch) => {
  return {
    onSetState(key, value) {
      dispatch({ type: 'SET_LIGHT_STATE', key, value })
    },
    onDispatch(action) {
      dispatch(action)
    },
  }
}

export default connect(mapStateToProps, mapDispatchToProps)(List)

使用useEffect也可以优化性能：

import React, { Suspense, useEffect, useState} from 'react'
import { Switch, Route } from 'react-router-dom'
import { connect } from 'react-redux'
import Loading from '../../../components/light/Loading'
import Header from './Header'
import Nav from './Nav'

function List(props) {
  const [listDom, setListDom] = useState([])
  const { router } = props


  // 只有router变化时才会重新渲染listDom，useEffect函数可以起到性能优化的作用
  useEffect(() => {
    const listDom = []
    const listRender = (arr) => {
      arr.forEach((item) => {
        if (item.children) {
          listRender(item.children)
        } else {
          listDom.push(
            <Route
              key={item.path}
              path={item.path}
              component={item.component}
            ></Route>
          )
        }
      })
    }
    listRender(router.toJS())
    setListDom(listDom)
  }, [router])


  return (
    <div className="m-list">
      <Header></Header>
      <div className="m-list-info">
        <Nav></Nav>
        <Suspense fallback={<Loading isLazyLoading={true}></Loading>}>
          <Switch>{listDom}</Switch>
        </Suspense>
      </div>
    </div>
  )
}

const mapStateToProps = (state) => {
  return {
    router: state.getIn(['light', 'router']),
    theme: state.getIn(['light', 'theme']),
  }
}

const mapDispatchToProps = (dispatch) => {
  return {
    onSetState(key, value) {
      dispatch({ type: 'SET_LIGHT_STATE', key, value })
    },
    onDispatch(action) {
      dispatch(action)
    },
  }
}

export default connect(mapStateToProps, mapDispatchToProps)(List)