react源码解析13.hooks源码
视频课程(高效学习):进入课程
课程目录:
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
21.demo
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
(// 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 | 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 = 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 = 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);