react源码解析14.手写hooks
视频解说（高效学习）：进入学习
往期文章：
1.开篇介绍和面试题
2.react的设计理念
3.react源码架构
4.源码目录构造和调试
5.jsx&外围api
6.legacy和concurrent模式入口函数
7.Fiber架构
8.render阶段
9.diff算法
10.commit阶段
11.生命周期
12.状态更新流程
13.hooks源码
14.手写hooks
15.scheduler&Lane
16.concurrent模式
17.context
18事件零碎
19.手写迷你版react
20.总结&第一章的面试题解答
最要害的是要了解hook队列和update队列的指针指向和updateQueue的更新计算，具体见视频解说
import React from "react";import ReactDOM from "react-dom";let workInProgressHook;//当前工作中的hooklet isMount = true;//是否时mount时const fiber = {//fiber节点 memoizedState: null,//hook链表 stateNode: App//dom};const Dispatcher = (() => {//Dispatcher对象 function mountWorkInProgressHook() {//mount时调用 const hook = {//构建hook queue: {//更新队列 pending: null//未执行的update队列 }, memoizedState: null,//以后state next: null//下一个hook }; if (!fiber.memoizedState) { fiber.memoizedState = hook;//第一个hook的话间接赋值给fiber.memoizedState } else { workInProgressHook.next = hook;//不是第一个的话就加在上一个hook的前面，造成链表 } workInProgressHook = hook;//记录当前工作的hook return workInProgressHook; } function updateWorkInProgressHook() {//update时调用 let curHook = workInProgressHook; workInProgressHook = workInProgressHook.next;//下一个hook return curHook; } function useState(initialState) { let hook; if (isMount) { hook = mountWorkInProgressHook(); hook.memoizedState = initialState;//初始状态 } else { hook = updateWorkInProgressHook(); } let baseState = hook.memoizedState;//初始状态 if (hook.queue.pending) { let firstUpdate = hook.queue.pending.next;//第一个update do { const action = firstUpdate.action; baseState = action(baseState); firstUpdate = firstUpdate.next;//循环update链表 } while (firstUpdate !== hook.queue.pending);//通过update的action计算state hook.queue.pending = null;//重置update链表 } hook.memoizedState = baseState;//赋值新的state return [baseState, dispatchAction.bind(null, hook.queue)];//useState的返回 } return { useState };})();function dispatchAction(queue, action) {//触发更新 const update = {//构建update action, next: null }; if (queue.pending === null) { update.next = update;//update的环状链表 } else { update.next = queue.pending.next;//新的update的next指向前一个update queue.pending.next = update;//前一个update的next指向新的update } queue.pending = update;//更新queue.pending isMount = false;//标记mount完结 workInProgressHook = fiber.memoizedState;//更新workInProgressHook schedule();//调度更新}function App() { let [count, setCount] = Dispatcher.useState(1); let [age, setAge] = Dispatcher.useState(10); return ( <> <p>Clicked {count} times</p> <button onClick={() => setCount(() => count + 1)}> Add count</button> <p>Age is {age}</p> <button onClick={() => setAge(() => age + 1)}> Add age</button> </> );}function schedule() { ReactDOM.render(<App />, document.querySelector("#root"));}schedule();