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react-hooks's Introduction

useState

  • params (state),return [state, setState]
  • 内部采用闭包,用 currentIndex 去记录 state 在 hookStates 数组中的位置
  • 调用 setState 设置值时,将 state 改变,并重置 hookIndex,重新渲染组件

useMemo

  • params (() => {key: value}, [deps]),return {key: value}
  • 初始以 [{key, value}, [deps]]形式 缓存在 hookStates 中
  • 读取时比较前后 deps 的变化,不变则读取缓存,发生改变则重新缓存

useCallback

  • params (() => fn, [deps]),return () => fn
  • 与 useMemo 实现基本一致

useEffect

  • params (callback, [deps]),return callback()
  • 初始以 [callback(), [deps]]形式 缓存在 hookStates 中
  • 读取时比较前后 deps 的变化,发生改变则调用 destroy 函数,重新缓存销毁函数和依赖

useLayoutEffect

  • 与 useEffect 基本一致,useEffect 用的是宏任务,useLayoutEffect 用的是微任务

useReducer

  • 与 useState 基本一致,在 hookStates 中记录了一个 reducer(state,action)

useContext

  • React.createContext() 会返回一个 context 将数据挂载到 _currentValue 上

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