react源码解析13.hooks源码 react.js

react源码解析13.hooks源码视频讲解（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.源码目录结构和调试
5.jsx&核心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事件系统
19.手写迷你版react
20.总结&第一章的面试题解答
hook调用入口 ? 在hook源码中hook存在于Dispatcher中，Dispatcher就是一个对象，不同hook 调用的函数不一样，全局变量ReactCurrentDispatcher.current会根据是mount还是update赋值为HooksDispatcherOnMount或HooksDispatcherOnUpdate

ReactCurrentDispatcher.current = current === null || current.memoizedState === null//mount or update ? HooksDispatcherOnMount : HooksDispatcherOnUpdate;

const HooksDispatcherOnMount: Dispatcher = {//mount时 useCallback: mountCallback, useContext: readContext, useEffect: mountEffect, useImperativeHandle: mountImperativeHandle, useLayoutEffect: mountLayoutEffect, useMemo: mountMemo, useReducer: mountReducer, useRef: mountRef, useState: mountState, //... }; const HooksDispatcherOnUpdate: Dispatcher = {//update时 useCallback: updateCallback, useContext: readContext, useEffect: updateEffect, useImperativeHandle: updateImperativeHandle, useLayoutEffect: updateLayoutEffect, useMemo: updateMemo, useReducer: updateReducer, useRef: updateRef, useState: updateState, //... };

hook数据结构 【react源码解析13.hooks源码】? 在FunctionComponent中，多个hook会形成hook链表，保存在Fiber的memoizedState的上，而需要更新的Update保存在hook.queue.pending中

const hook: Hook = { memoizedState: null,//对于不同hook，有不同的值 baseState: null,//初始state baseQueue: null,//初始queue队列 queue: null,//需要更新的update next: null,//下一个hook };

下面来看下memoizedState对应的值

useState：例如const [state, updateState] = useState(initialState)，memoizedState等于state的值
useReducer：例如const [state, dispatch] = useReducer(reducer, {});，memoizedState等于state的值
useEffect：在mountEffect时会调用pushEffect创建effect链表，memoizedState就等于effect链表，effect链表也会挂载到fiber.updateQueue上，每个effect上存在useEffect的第一个参数回调和第二个参数依赖数组，例如，useEffect(callback, [dep])，effect就是{create:callback, dep:dep,...}
useRef：例如useRef(0)，memoizedState就等于{current: 0}
useMemo：例如useMemo(callback, [dep])，memoizedState等于[callback(), dep]
useCallback：例如useCallback(callback, [dep])，memoizedState等于[callback, dep]。useCallback保存callback函数，useMemo保存callback的执行结果

useState&useReducer 之所以把useState和useReducer放在一起，是因为在源码中useState就是有默认reducer参数的useReducer。

useState&useReducer声明
? resolveDispatcher函数会获取当前的Dispatcher

function useState(initialState) { var dispatcher = resolveDispatcher(); return dispatcher.useState(initialState); } function useReducer(reducer, initialArg, init) { var dispatcher = resolveDispatcher(); return dispatcher.useReducer(reducer, initialArg, init); }

mount阶段
? mount阶段useState调用mountState，useReducer调用mountReducer，唯一区别就是它们创建的queue中lastRenderedReducer不一样，mount有初始值basicStateReducer，所以说useState就是有默认reducer参数的useReducer。

function mountState(// initialState: (() => S) | S, ): [S, Dispatch] { const hook = mountWorkInProgressHook(); //创建当前hook if (typeof initialState === 'function') { initialState = initialState(); } hook.memoizedState = hook.baseState = initialState; //hook.memoizedState赋值 const queue = (hook.queue = {//赋值hook.queue pending: null, dispatch: null, lastRenderedReducer: basicStateReducer,//和mountReducer的区别 lastRenderedState: (initialState: any), }); const dispatch: Dispatch = (queue.dispatch = (dispatchAction.bind( null, currentlyRenderingFiber, queue, ): any)); return [hook.memoizedState, dispatch]; //返回memoizedState和dispatch }function mountReducer( reducer: (S, A) => S, initialArg: I, init?: I => S, ): [S, Dispatch] { const hook = mountWorkInProgressHook(); //创建当前hook let initialState; if (init !== undefined) { initialState = init(initialArg); } else { initialState = ((initialArg: any): S); } hook.memoizedState = hook.baseState = initialState; //hook.memoizedState赋值 const queue = (hook.queue = {//创建queue pending: null, dispatch: null, lastRenderedReducer: reducer, lastRenderedState: (initialState: any), }); const dispatch: Dispatch = (queue.dispatch = (dispatchAction.bind(//创建dispatch函数 null, currentlyRenderingFiber, queue, ): any)); return [hook.memoizedState, dispatch]; //返回memoizedState和dispatch }

function basicStateReducer(state: S, action: BasicStateAction): S { return typeof action === 'function' ? action(state) : action; }

update阶段
update时会根据hook中的update计算新的state

function updateReducer( reducer: (S, A) => S, initialArg: I, init?: I => S, ): [S, Dispatch] { const hook = updateWorkInProgressHook(); //获取hook const queue = hook.queue; queue.lastRenderedReducer = reducer; //...更新state和第12章的state计算逻辑基本一致const dispatch: Dispatch = (queue.dispatch: any); return [hook.memoizedState, dispatch]; }

执行阶段
useState执行setState后会调用dispatchAction，dispatchAction做的事情就是讲Update加入queue.pending中，然后开始调度

function dispatchAction(fiber, queue, action) {var update = {//创建update eventTime: eventTime, lane: lane, suspenseConfig: suspenseConfig, action: action, eagerReducer: null, eagerState: null, next: null }; //queue.pending中加入updatevar alternate = fiber.alternate; if (fiber === currentlyRenderingFiber$1 || alternate !== null && alternate === currentlyRenderingFiber$1) { //如果是render阶段执行的更新didScheduleRenderPhaseUpdate=true } didScheduleRenderPhaseUpdateDuringThisPass = didScheduleRenderPhaseUpdate = true; } else { if (fiber.lanes === NoLanes && (alternate === null || alternate.lanes === NoLanes)) { //如果fiber不存在优先级并且当前alternate不存在或者没有优先级，那就不需要更新了 //优化的步骤 }scheduleUpdateOnFiber(fiber, lane, eventTime); } }

useEffect

声明
获取并返回useEffect函数

export function useEffect( create: () => (() => void) | void, deps: Array | void | null, ): void { const dispatcher = resolveDispatcher(); return dispatcher.useEffect(create, deps); }

mount阶段
? 调用mountEffect，mountEffect调用mountEffectImpl，hook.memoizedState赋值为effect链表

function mountEffectImpl(fiberFlags, hookFlags, create, deps): void { const hook = mountWorkInProgressHook(); //获取hook const nextDeps = deps === undefined ? null : deps; //依赖 currentlyRenderingFiber.flags |= fiberFlags; //增加flag hook.memoizedState = pushEffect(//memoizedState=effects环状链表 HookHasEffect | hookFlags, create, undefined, nextDeps, ); }

update阶段
? 浅比较依赖，如果依赖性变了pushEffect第一个参数传HookHasEffect | hookFlags，HookHasEffect表示useEffect依赖项改变了，需要在commit阶段重新执行

function updateEffectImpl(fiberFlags, hookFlags, create, deps): void { const hook = updateWorkInProgressHook(); const nextDeps = deps === undefined ? null : deps; let destroy = undefined; if (currentHook !== null) { const prevEffect = currentHook.memoizedState; destroy = prevEffect.destroy; // if (nextDeps !== null) { const prevDeps = prevEffect.deps; if (areHookInputsEqual(nextDeps, prevDeps)) {//比较deps //即使依赖相等也要将effect加入链表，以保证顺序一致 pushEffect(hookFlags, create, destroy, nextDeps); return; } } }currentlyRenderingFiber.flags |= fiberFlags; hook.memoizedState = pushEffect( //参数传HookHasEffect | hookFlags，包含hookFlags的useEffect会在commit阶段执行这个effect HookHasEffect | hookFlags, create, destroy, nextDeps, ); }

执行阶段
? 在第9章commit阶段的commitLayoutEffects函数中会调用schedulePassiveEffects，将useEffect的销毁和回调函数push到pendingPassiveHookEffectsUnmount和pendingPassiveHookEffectsMount中，然后在mutation之后调用flushPassiveEffects依次执行上次render的销毁函数回调和本次render 的回调函数

const unmountEffects = pendingPassiveHookEffectsUnmount; pendingPassiveHookEffectsUnmount = []; for (let i = 0; i < unmountEffects.length; i += 2) { const effect = ((unmountEffects[i]: any): HookEffect); const fiber = ((unmountEffects[i + 1]: any): Fiber); const destroy = effect.destroy; effect.destroy = undefined; if (typeof destroy === 'function') { try { destroy(); //销毁函数执行 } catch (error) { captureCommitPhaseError(fiber, error); } } }const mountEffects = pendingPassiveHookEffectsMount; pendingPassiveHookEffectsMount = []; for (let i = 0; i < mountEffects.length; i += 2) { const effect = ((mountEffects[i]: any): HookEffect); const fiber = ((mountEffects[i + 1]: any): Fiber); try { const create = effect.create; //本次render的创建函数 effect.destroy = create(); } catch (error) { captureCommitPhaseError(fiber, error); } }

useRef ? sring类型的ref已经不在推荐使用(源码中string会生成refs，发生在coerceRef函数中)，ForwardRef只是把ref通过传参传下去，createRef也是{current: any这种结构，所以我们只讨论function或者{current: any}的useRef

//createRef返回{current: any} export function createRef(): RefObject { const refObject = { current: null, }; return refObject; }

声明阶段
? 和其他hook一样

export function useRef(initialValue: T): {|current: T|} { const dispatcher = resolveDispatcher(); return dispatcher.useRef(initialValue); }

mount阶段
? mount时会调用mountRef，创建hook和ref对象。

function mountRef(initialValue: T): {|current: T|} { const hook = mountWorkInProgressHook(); //获取useRef const ref = {current: initialValue}; //ref初始化 hook.memoizedState = ref; return ref; }

? render阶段：将带有ref属性的Fiber标记上Ref Tag，这一步发生在beginWork和completeWork函数中的markRef

export const Ref = /**/ 0b0000000010000000;

//beginWork中 function markRef(current: Fiber | null, workInProgress: Fiber) { const ref = workInProgress.ref; if ( (current === null && ref !== null) || (current !== null && current.ref !== ref) ) { workInProgress.effectTag |= Ref; } } //completeWork中 function markRef(workInProgress: Fiber) { workInProgress.effectTag |= Ref; }

? commit阶段：
? 会在commitMutationEffects函数中判断ref是否改变，如果改变了会先执行commitDetachRef先删除之前的ref，然后在commitLayoutEffect中会执行commitAttachRef赋值ref。

function commitMutationEffects(root: FiberRoot, renderPriorityLevel) { while (nextEffect !== null) { const effectTag = nextEffect.effectTag; // ...if (effectTag & Ref) { const current = nextEffect.alternate; if (current !== null) { commitDetachRef(current); //移除ref } } }

function commitDetachRef(current: Fiber) { const currentRef = current.ref; if (currentRef !== null) { if (typeof currentRef === 'function') { currentRef(null); //类型是function，则调用 } else { currentRef.current = null; //否则赋值{current: null} } } }

function commitAttachRef(finishedWork: Fiber) { const ref = finishedWork.ref; if (ref !== null) { const instance = finishedWork.stateNode; //获取ref的实例 let instanceToUse; switch (finishedWork.tag) { case HostComponent: instanceToUse = getPublicInstance(instance); break; default: instanceToUse = instance; }if (typeof ref === 'function') {//ref赋值 ref(instanceToUse); } else { ref.current = instanceToUse; } } }

update阶段
? update时调用updateRef获取获取当前useRef，然后返回hook链表

function updateRef(initialValue: T): {|current: T|} { const hook = updateWorkInProgressHook(); //获取当前useRef return hook.memoizedState; //返回hook链表 }

useMemo&useCallback

声明阶段
和其他hook 一样
mount阶段
mount阶段useMemo和useCallback唯一区别是在memoizedState中存贮callback还是callback计算出来的函数

function mountMemo( nextCreate: () => T, deps: Array | void | null, ): T { const hook = mountWorkInProgressHook(); //创建hook const nextDeps = deps === undefined ? null : deps; const nextValue = https://www.it610.com/article/nextCreate(); //计算value hook.memoizedState = [nextValue, nextDeps]; //把value和依赖保存在memoizedState中 return nextValue; }function mountCallback(callback: T, deps: Array | void | null): T { const hook = mountWorkInProgressHook(); //创建hook const nextDeps = deps === undefined ? null : deps; hook.memoizedState = [callback, nextDeps]; //把callback和依赖保存在memoizedState中 return callback; }

update阶段
update时也一样，唯一区别就是直接用回调函数还是执行回调后返回的value作为[?, nextDeps]赋值给memoizedState

function updateMemo( nextCreate: () => T, deps: Array | void | null, ): T { const hook = updateWorkInProgressHook(); //获取hook const nextDeps = deps === undefined ? null : deps; const prevState = hook.memoizedState; if (prevState !== null) { if (nextDeps !== null) { const prevDeps: Array | null = prevState[1]; if (areHookInputsEqual(nextDeps, prevDeps)) {//浅比较依赖 return prevState[0]; //没变返回之前的状态 } } } const nextValue = https://www.it610.com/article/nextCreate(); //有变化重新调用callback hook.memoizedState = [nextValue, nextDeps]; return nextValue; }function updateCallback(callback: T, deps: Array | void | null): T { const hook = updateWorkInProgressHook(); //获取hook const nextDeps = deps === undefined ? null : deps; const prevState = hook.memoizedState; if (prevState !== null) { if (nextDeps !== null) { const prevDeps: Array | null = prevState[1]; if (areHookInputsEqual(nextDeps, prevDeps)) {//浅比较依赖 return prevState[0]; //没变返回之前的状态 } } }hook.memoizedState = [callback, nextDeps]; //变了重新将[callback, nextDeps]赋值给memoizedState return callback; }

useLayoutEffect useLayoutEffect和useEffect一样，只是调用的时机不同，它是在commit阶段的commitLayout函数中同步执行
forwardRef forwardRef也非常简单，就是传递ref属性

export function forwardRef( render: (props: Props, ref: React$Ref) => React$Node, ) {const elementType = { $$typeof: REACT_FORWARD_REF_TYPE, render, }; return elementType; } //ForwardRef第二个参数是ref对象 let children = Component(props, secondArg);