zoukankan      html  css  js  c++  java
  • [React] When to useReducer instead of useState

    useState is typically simpler at first than useReducer (you can even implement useState using useReducer), but there's one scenario where useReducer is almost certainly better than useState:

    When one element of your state relies on the value of another element of your state in order to update: useReducer

    More information: KcD's blog

    import React from 'react'
    import ReactDOM from 'react-dom'
    
    function undoReducer(state, action) {
      const {past, present, future} = state
      const {type, newPresent} = action
    
      switch (type) {
        case 'UNDO': {
          if (past.length === 0) return state
    
          const previous = past[past.length - 1]
          const newPast = past.slice(0, past.length - 1)
          return {
            past: newPast,
            present: previous,
            future: [present, ...future],
          }
        }
        case 'REDO': {
          if (future.length === 0) return state
          const next = future[0]
          const newFuture = future.slice(1)
          return {
            past: [...past, present],
            present: next,
            future: newFuture,
          }
        }
        case 'SET': {
          if (newPresent === present) {
            return state
          }
          return {
            past: [...past, present],
            present: newPresent,
            future: [],
          }
        }
        case 'RESET': {
          return {
            past: [],
            present: newPresent,
            future: [],
          }
        }
        default: {
          throw new Error(`Unhandled action type: ${type}`)
        }
      }
    }
    
    function useUndo(initialPresent) {
      const [state, dispatch] = React.useReducer(undoReducer, {
        past: [],
        present: initialPresent,
        future: [],
      })
    
      const canUndo = state.past.length !== 0
      const canRedo = state.future.length !== 0
    
      const undo = React.useCallback(() => {
        dispatch({type: 'UNDO'})
      }, [])
    
      const redo = React.useCallback(() => {
        dispatch({type: 'REDO'})
      }, [])
    
      const set = React.useCallback(newPresent => {
        dispatch({type: 'SET', newPresent})
      }, [])
    
      const reset = React.useCallback(newPresent => {
        dispatch({type: 'RESET', newPresent})
      }, [])
    
      return [state, {set, reset, undo, redo, canUndo, canRedo}]
    }
    
    function App() {
      const [state, {set}] = useUndo('first')
    
      React.useEffect(() => {
        set('second')
      }, [set])
    
      React.useEffect(() => {
        set('third')
      }, [set])
    
      return <pre>{JSON.stringify(state, null, 2)}</pre>
    }
    
    ReactDOM.render(<App />, document.getElementById('root'))
  • 相关阅读:
    使用sublimehighlight 将文本 转化html
    iOS- 制作U盘安装Mac OS X 系统
    垃圾回收的常见算法
    jvm的三种参数类型
    HashMap遍历取值
    不要在 foreach 循环里进行元素的 remove/add 操作
    Arrays.asList()使用指南
    正确使用 equals 方法
    elasticsearch安装与配置(在Linux环境下配置)
    本地访问Linux里端口连接失败
  • 原文地址:https://www.cnblogs.com/Answer1215/p/12464013.html
Copyright © 2011-2022 走看看