useState原理

转发 blog.csdn.net/chenzhizhuo…

示例

import React, {useState} from 'react'
const AddCount = () => {
  const [ count, setCount ] = useState(0)
  const addcount = () => {
    let newCount = count
    setCount(newCount+=1)
  } 
  return (
    <>
      <p>{count}</p>
      <button onClick={addcount}>count++</button>
    </>
  )
}

useState原理

// 我们实现一个简易版的useState
let memoizedStates = [ ]  // 多个useState 时需要使用数组来存
let index = 0
function useState (initialState) {
   memoizedStates[index] = memoizedStates[index] || initialState
   let currentIndex = index;
   function setState (newState) {
      memoizedStates[currentIndex] = newState
      render()
   }
   return [memoizedStates[index++], setState]
}