人人都能读懂的react源码解析(大厂高薪必备)
9.hooks源码(想知道Function Component是怎样保存状态的嘛)
视频课程&调试demos
视频课程的目的是为了快速掌握react源码运行的过程和react中的scheduler、reconciler、renderer、fiber等，并且详细debug源码和分析，过程更清晰。
视频课程：进入课程
demos：demo
课程结构:
- 开篇(听说你还在艰难的啃react源码)
- react心智模型(来来来,让大脑有react思维吧)
- Fiber(我是在内存中的dom)
- 从legacy或concurrent开始(从入口开始,然后让我们奔向未来)
- state更新流程(setState里到底发生了什么)
- render阶段(厉害了,我有创建Fiber的技能)
- commit阶段(听说renderer帮我们打好标记了,映射真实节点吧)
- diff算法(妈妈再也不担心我的diff面试了)
- hooks源码(想知道Function Component是怎样保存状态的嘛)
- scheduler&lane模型(来看看任务是暂停、继续和插队的)
- concurrent mode(并发模式是什么样的)
- 手写迷你react(短小精悍就是我)
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
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<S>(// initialState: (() => S) | S, ): [S, Dispatch<BasicStateAction<S>>] { 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<//创建dispatch函数 BasicStateAction<S>, > = (queue.dispatch = (dispatchAction.bind( null, currentlyRenderingFiber, quewque, ): any)); return [hook.memoizedState, dispatch];//返回memoizedState和dispatch } function mountReducer<S, I, A>( reducer: (S, A) => S, initialArg: I, init?: I => S, ): [S, Dispatch<A>] { 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<A> = (queue.dispatch = (dispatchAction.bind(//创建dispatch函数 null, currentlyRenderingFiber, queue, ): any)); return [hook.memoizedState, dispatch];//返回memoizedState和dispatch }function basicStateReducer<S>(state: S, action: BasicStateAction<S>): 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<S, I, A>( reducer: (S, A) => S, initialArg: I, init?: I => S, ): [S, Dispatch<A>] { const hook = updateWorkInProgressHook();//获取hook const queue = hook.queue; queue.lastRenderedReducer = reducer; //...更新state和第5章的state计算逻辑基本一致 const dispatch: Dispatch<A> = (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update var 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<mixed> | 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，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;
}
//ForwardRef第二个参数是ref对象
let children = Component(props, secondArg);
-
声明阶段
和其他hook一样
export function useRef<T>(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<T>(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，在一步发生在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<T>(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<T>( nextCreate: () => T, deps: Array<mixed> | void | null, ): T { const hook = mountWorkInProgressHook();//创建hook const nextDeps = deps === undefined ? null : deps; const nextValue = nextCreate();//计算value hook.memoizedState = [nextValue, nextDeps];//把value和依赖保存在memoizedState中 return nextValue; } function mountCallback<T>(callback: T, deps: Array<mixed> | 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<T>(
nextCreate: () => T,
deps: Array<mixed> | 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<mixed> | 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 = nextCreate();//有变化重新调用callback
hook.memoizedState = [nextValue, nextDeps];
return nextValue;
}
function updateCallback<T>(callback: T, deps: Array<mixed> | 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<mixed> | 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;
}
