1.解读useEffect和useLayouEffect原理
2.解读useEffectåuseLayouEffectåç
解读useEffect和useLayouEffect原理
背景
写这篇文章是源码因为工作上不是非常繁忙,可以抽空学习自己常用框架和类库,源码深入理解它们,源码在技术上希望有更大的源码进步,培养学习兴趣;
useEffect和其它hooks一样,源码加载和更新执行不一样的源码永恒e盘源码方法(mountEffect和updateEffect);
1.mountEffect页面加载时,执行mountEffect;
创建hook对象,源码加入组件的源码hook单向链表;
在组件的fiber的flag中加入副作用相关的effectTag;(加载期间默认有layoutEffect和effect的副作用)
创建effect对象,给hook对象的源码memoizedState和加入组件fiber的updateQueue中形成effect环状链表;在渲染工作完成后,会循环这个环状链表,源码执行每个effect对象的源码destory和create;
consteffect={ tag,create,destroy,deps,next:null};tag是effect的类型tag为9是useEffect,5是useLayoutEffectcreate是useEffect或useLayoutEffect的回调函数destroy是create返回的回调函数deps是useEffect或useLayoutEffect的依赖数组next指向下个effect对象;1.1.effect环状链表图functionpushEffect(tag,create,destroy,deps){ consteffect={ tag,create,destroy,deps,next:null};//新创建的effect对象为最后为effect链表的一个effect对象,componentUpdateQueue.lastEffect会指向新创建的源码effect对象//新创建的effect对象的next会指向第一个effct对象;letcomponentUpdateQueue=(currentlyRenderingFiber.updateQueue);if(componentUpdateQueue===null){ //当前没有updateQueuecomponentUpdateQueue=createFunctionComponentUpdateQueue();//创建updateQueuecurrentlyRenderingFiber.updateQueue=componentUpdateQueue;//形成一个环状链表componentUpdateQueue.lastEffect=effect.next=effect}else{ constlastEffect=componentUpdateQueue.lastEffect;if(lastEffect===null){ componentUpdateQueue.lastEffect=effect.next=effect;}else{ //第一个effect对象为最先创建的的effect对象constfirstEffect=lastEffect.next;//获取第一个effect对象lastEffect.next=effect;//旧的最后一个effect对象的next,指向新创建的源码effecteffect.next=firstEffect;//新创建的effect对象的next指向第一个effectcomponentUpdateQueue.lastEffect=effect;//updateQueue的lastEffect指向effect,新创建的源码effect变为最后一个effect对象}}returneffect;}2.updateEffect页面更新时,执行updateEffect;
根据hook单向链表获取对应的源码源码侵权处罚更新时的hook对象,创建新的hook对象,加入hook单向链表;
如果effect的deps不为null,或者undefined,会从当前hook对象拿到上一次effect对象,再从effect对象拿到deps和destroy,用新的deps与之比较;
如果新老deps相等,push一个不带HookHasEffect的github源码readmetag给effect对象,加入updateQueue环状链表(这个effect不会被标记为有副作用,所以,effect的create和destroy不会被执行),不更新hook.memoizedState;
如果新老deps不相等,更新effect对象,在effect的tag中加入HookHasEffect和上一次create执行的destroy,更新hook.memoizedState;
3.useEffct的地球图源码回调函数和销毁函数的执行时机在render时期构建effect链表;在commit时执行先执行之前没有执行完的useEffect,然后,在beforeMutation阶段操作dom前,以NormalPriority常规优先级添加一个异步任务到任务队列(这个异步任务是用来执行useEffect的destroy和create的),在layout阶段完成,页面完成渲染后,执行在beforeMutation阶段添加的异步任务;
3.1.commit开始时主要是为了执行之前没有执行的useEffect
进入commit阶段,这和useEffect异步调度的rai源码网特点有关,它以一般的优先级被调度,意味着一旦有更高优先级的任务进入到commit阶段,上一次任务的useEffect还没得到执行。所以在本次更新开始前,需要先将之前的useEffect都执行掉,以保证本次调度的useEffect都是本次更新产生的。
functioncommitRootImpl(root,recoverableErrors,renderPriorityLevel){ do{ //`flushPassiveEffects`willcall`flushSyncUpdateQueue`attheend,which//means`flushPassiveEffects`willsometimesresultinadditional//passiveeffects.Soweneedtokeepflushinginaloopuntilthereare//nomorependingeffects.//TODO:Mightbebetterif`flushPassiveEffects`didnotautomatically//flushsynchronousworkattheend,toavoidfactoringhazardslikethis.flushPassiveEffects();}while(rootWithPendingPassiveEffects!==null);...省略代码}3.2.beforeMutation只会发起一次useEffect调度,是异步调度,以NormalPriority常规优先级添加一个异步任务在任务队列中(push(timerQueue,newTask)),在页面渲染完成时,会执行这个异步任务
functioncommitRootImpl(root,recoverableErrors,renderPriorityLevel){ ...省略代码if((finishedWork.subtreeFlags&PassiveMask)!==NoFlags||(finishedWork.flags&PassiveMask)!==NoFlags){ if(!rootDoesHavePassiveEffects){ rootDoesHavePassiveEffects=true;scheduleCallback$1(NormalPriority,function(){ //添加一个异步任务到任务队列flushPassiveEffects();//Thisrendertriggeredpassiveeffects:releasetherootcachepool//*after*passiveeffectsfiretoavoidfreeingacachepoolthatmay//bereferencedbyanodeinthetree(HostRoot,Cacheboundaryetc)returnnull;});}}...省略代码}3.3.layout加载时,只执行useEffect的create函数即可;
如果pendingPassiveEffectsLanes是同步赛道,就在页面渲染完直接执行useEffect的create和destroy,在beforeMutation时添加的异步任务,不会执行useEffect的create和destory
if(includesSomeLane(pendingPassiveEffectsLanes,SyncLane)&&root.tag!==LegacyRoot){ //加载期间默认是不走这里的//这里也是执行useEffect的create,如果pendingPassiveEffectsLanes是同步赛道,//就在渲染完成后直接执行useEffect的create和destory//在beforeMutation时添加的异步任务执行时,不会执行useEffect的create和destoryflushPassiveEffects();}执行上一次useEffect的create返回的destroy,拿到函数组件fiber的updateQueue,循环这个effect环状链表,拿到effect对象的destroy执行;
functioncommitHookEffectListUnmount(flags,finishedWork,nearestMountedAncestor){ varupdateQueue=finishedWork.updateQueue;varlastEffect=updateQueue!==null?updateQueue.lastEffect:null;if(lastEffect!==null){ varfirstEffect=lastEffect.next;vareffect=firstEffect;do{ if((effect.tag&flags)===flags){ //Unmountvardestroy=effect.destroy;effect.destroy=undefined;if(destroy!==undefined){ { if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectUnmountStarted(finishedWork);}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectUnmountStarted(finishedWork);}}safelyCallDestroy(finishedWork,nearestMountedAncestor,destroy);//执行destroy{ if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectUnmountStopped();}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectUnmountStopped();}}}}effect=effect.next;}while(effect!==firstEffect);}}执行完所有组件的destroy,再执行create;同理,也是拿到函数组件fiber的updateQueue,循环这个effect环状链表,拿到effect对象的create执行,然后把create返回的destroy给effect对象(留着下着更新执行useEffect时用);
functioncommitHookEffectListMount(flags,finishedWork){ varupdateQueue=finishedWork.updateQueue;varlastEffect=updateQueue!==null?updateQueue.lastEffect:null;if(lastEffect!==null){ varfirstEffect=lastEffect.next;vareffect=firstEffect;do{ if((effect.tag&flags)===flags){ { if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectMountStarted(finishedWork);}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectMountStarted(finishedWork);}}//Mountvarcreate=effect.create;effect.destroy=create();{ if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectMountStopped();}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectMountStopped();}}{ vardestroy=effect.destroy;if(destroy!==undefined&&typeofdestroy!=='function'){ varhookName=void0;if((effect.tag&Layout)!==NoFlags){ hookName='useLayoutEffect';}elseif((effect.tag&Insertion)!==NoFlags){ hookName='useInsertionEffect';}else{ hookName='useEffect';}varaddendum=void0;if(destroy===null){ addendum='Youreturnednull.Ifyoureffectdoesnotrequireclean'+'up,returnundefined(ornothing).';}elseif(typeofdestroy.then==='function'){ addendum='\n\nItlookslikeyouwrote'+hookName+'(async()=>...)orreturnedaPromise.'+'Instead,writetheasyncfunctioninsideyoureffect'+'andcallitimmediately:\n\n'+hookName+'(()=>{ \n'+'asyncfunctionfetchData(){ \n'+'//Youcanawaithere\n'+'constresponse=awaitMyAPI.getData(someId);\n'+'//...\n'+'}\n'+'fetchData();\n'+"},[someId]);//Or[]ifeffectdoesn'tneedpropsorstate\n\n"+'LearnmoreaboutdatafetchingwithHooks:/post/解读useEffectåuseLayouEffectåç
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å建hook对象ï¼å å ¥ç»ä»¶çhookååé¾è¡¨ï¼
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å建effect对象ï¼ç»hook对象çmemoizedStateåå å ¥ç»ä»¶fiberçupdateQueueä¸å½¢æeffectç¯ç¶é¾è¡¨ï¼å¨æ¸²æå·¥ä½å®æåï¼ä¼å¾ªç¯è¿ä¸ªç¯ç¶é¾è¡¨ï¼æ§è¡æ¯ä¸ªeffect对象çdestoryåcreateï¼
consteffect={ tag,create,destroy,deps,next:null};tagæ¯effectçç±»åtag为9æ¯useEffect,5æ¯useLayoutEffectcreateæ¯useEffectæuseLayoutEffectçåè°å½æ°destroyæ¯createè¿åçåè°å½æ°depsæ¯useEffectæuseLayoutEffectçä¾èµæ°ç»nextæåä¸ä¸ªeffect对象ï¼1.1.effectç¯ç¶é¾è¡¨å¾functionpushEffect(tag,create,destroy,deps){ consteffect={ tag,create,destroy,deps,next:null};//æ°å建çeffect对象为æå为effecté¾è¡¨çä¸ä¸ªeffect对象ï¼componentUpdateQueue.lastEffectä¼æåæ°å建çeffect对象//æ°å建çeffect对象çnextä¼æå第ä¸ä¸ªeffct对象ï¼letcomponentUpdateQueue=(currentlyRenderingFiber.updateQueue);if(componentUpdateQueue===null){ //å½å没æupdateQueuecomponentUpdateQueue=createFunctionComponentUpdateQueue();//å建updateQueuecurrentlyRenderingFiber.updateQueue=componentUpdateQueue;//å½¢æä¸ä¸ªç¯ç¶é¾è¡¨componentUpdateQueue.lastEffect=effect.next=effect}else{ constlastEffect=componentUpdateQueue.lastEffect;if(lastEffect===null){ componentUpdateQueue.lastEffect=effect.next=effect;}else{ //第ä¸ä¸ªeffect对象为æå å建ççeffect对象constfirstEffect=lastEffect.next;//è·å第ä¸ä¸ªeffect对象lastEffect.next=effect;//æ§çæåä¸ä¸ªeffect对象çnextï¼æåæ°å建çeffecteffect.next=firstEffect;//æ°å建çeffect对象çnextæå第ä¸ä¸ªeffectcomponentUpdateQueue.lastEffect=effect;//updateQueueçlastEffectæåeffectï¼æ°å建çeffectå为æåä¸ä¸ªeffect对象}}returneffect;}2.updateEffect页é¢æ´æ°æ¶ï¼æ§è¡updateEffect;
æ ¹æ®hookååé¾è¡¨è·å对åºçæ´æ°æ¶çhook对象ï¼å建æ°çhook对象ï¼å å ¥hookååé¾è¡¨ï¼
å¦æeffectçdepsä¸ä¸ºnullï¼æè undefinedï¼ä¼ä»å½åhook对象æ¿å°ä¸ä¸æ¬¡effect对象ï¼åä»effect对象æ¿å°depsådestroyï¼ç¨æ°çdepsä¸ä¹æ¯è¾ï¼
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3.1.commitå¼å§æ¶ä¸»è¦æ¯ä¸ºäºæ§è¡ä¹å没ææ§è¡çuseEffect
è¿å ¥commité¶æ®µï¼è¿åuseEffectå¼æ¥è°åº¦çç¹ç¹æå ³ï¼å®ä»¥ä¸è¬çä¼å 级被è°åº¦ï¼æå³çä¸æ¦ææ´é«ä¼å 级çä»»å¡è¿å ¥å°commité¶æ®µï¼ä¸ä¸æ¬¡ä»»å¡çuseEffectè¿æ²¡å¾å°æ§è¡ãæ以å¨æ¬æ¬¡æ´æ°å¼å§åï¼éè¦å å°ä¹åçuseEffecté½æ§è¡æï¼ä»¥ä¿è¯æ¬æ¬¡è°åº¦çuseEffecté½æ¯æ¬æ¬¡æ´æ°äº§ççã
functioncommitRootImpl(root,recoverableErrors,renderPriorityLevel){ do{ //`flushPassiveEffects`willcall`flushSyncUpdateQueue`attheend,which//means`flushPassiveEffects`willsometimesresultinadditional//passiveeffects.Soweneedtokeepflushinginaloopuntilthereare//nomorependingeffects.//TODO:Mightbebetterif`flushPassiveEffects`didnotautomatically//flushsynchronousworkattheend,toavoidfactoringhazardslikethis.flushPassiveEffects();}while(rootWithPendingPassiveEffects!==null);...çç¥ä»£ç }3.2.beforeMutationåªä¼åèµ·ä¸æ¬¡useEffectè°åº¦ï¼æ¯å¼æ¥è°åº¦ï¼ä»¥NormalPriority常è§ä¼å 级添å ä¸ä¸ªå¼æ¥ä»»å¡å¨ä»»å¡éåä¸ï¼push(timerQueue,newTask)ï¼ï¼å¨é¡µé¢æ¸²æå®ææ¶ï¼ä¼æ§è¡è¿ä¸ªå¼æ¥ä»»å¡
functioncommitRootImpl(root,recoverableErrors,renderPriorityLevel){ ...çç¥ä»£ç if((finishedWork.subtreeFlags&PassiveMask)!==NoFlags||(finishedWork.flags&PassiveMask)!==NoFlags){ if(!rootDoesHavePassiveEffects){ rootDoesHavePassiveEffects=true;scheduleCallback$1(NormalPriority,function(){ //æ·»å ä¸ä¸ªå¼æ¥ä»»å¡å°ä»»å¡éåflushPassiveEffects();//Thisrendertriggeredpassiveeffects:releasetherootcachepool//*after*passiveeffectsfiretoavoidfreeingacachepoolthatmay//bereferencedbyanodeinthetree(HostRoot,Cacheboundaryetc)returnnull;});}}...çç¥ä»£ç }3.3.layoutå è½½æ¶ï¼åªæ§è¡useEffectçcreateå½æ°å³å¯ï¼
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if(includesSomeLane(pendingPassiveEffectsLanes,SyncLane)&&root.tag!==LegacyRoot){ //å è½½æé´é»è®¤æ¯ä¸èµ°è¿éç//è¿éä¹æ¯æ§è¡useEffectçcreateï¼å¦æpendingPassiveEffectsLanesæ¯åæ¥èµéï¼//å°±å¨æ¸²æå®æåç´æ¥æ§è¡useEffectçcreateådestory//å¨beforeMutationæ¶æ·»å çå¼æ¥ä»»å¡æ§è¡æ¶ï¼ä¸ä¼æ§è¡useEffectçcreateådestoryflushPassiveEffects();}æ§è¡ä¸ä¸æ¬¡useEffectçcreateè¿åçdestroyï¼æ¿å°å½æ°ç»ä»¶fiberçupdateQueueï¼å¾ªç¯è¿ä¸ªeffectç¯ç¶é¾è¡¨ï¼æ¿å°effect对象çdestroyæ§è¡ï¼
functioncommitHookEffectListUnmount(flags,finishedWork,nearestMountedAncestor){ varupdateQueue=finishedWork.updateQueue;varlastEffect=updateQueue!==null?updateQueue.lastEffect:null;if(lastEffect!==null){ varfirstEffect=lastEffect.next;vareffect=firstEffect;do{ if((effect.tag&flags)===flags){ //Unmountvardestroy=effect.destroy;effect.destroy=undefined;if(destroy!==undefined){ { if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectUnmountStarted(finishedWork);}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectUnmountStarted(finishedWork);}}safelyCallDestroy(finishedWork,nearestMountedAncestor,destroy);//æ§è¡destroy{ if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectUnmountStopped();}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectUnmountStopped();}}}}effect=effect.next;}while(effect!==firstEffect);}}æ§è¡å®ææç»ä»¶çdestroyï¼åæ§è¡createï¼åçï¼ä¹æ¯æ¿å°å½æ°ç»ä»¶fiberçupdateQueueï¼å¾ªç¯è¿ä¸ªeffectç¯ç¶é¾è¡¨ï¼æ¿å°effect对象çcreateæ§è¡ï¼ç¶åæcreateè¿åçdestroyç»effect对象ï¼ççä¸çæ´æ°æ§è¡useEffectæ¶ç¨ï¼ï¼
functioncommitHookEffectListMount(flags,finishedWork){ varupdateQueue=finishedWork.updateQueue;varlastEffect=updateQueue!==null?updateQueue.lastEffect:null;if(lastEffect!==null){ varfirstEffect=lastEffect.next;vareffect=firstEffect;do{ if((effect.tag&flags)===flags){ { if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectMountStarted(finishedWork);}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectMountStarted(finishedWork);}}//Mountvarcreate=effect.create;effect.destroy=create();{ if((flags&Passive$1)!==NoFlags$1){ markComponentPassiveEffectMountStopped();}elseif((flags&Layout)!==NoFlags$1){ markComponentLayoutEffectMountStopped();}}{ vardestroy=effect.destroy;if(destroy!==undefined&&typeofdestroy!=='function'){ varhookName=void0;if((effect.tag&Layout)!==NoFlags){ hookName='useLayoutEffect';}elseif((effect.tag&Insertion)!==NoFlags){ hookName='useInsertionEffect';}else{ hookName='useEffect';}varaddendum=void0;if(destroy===null){ addendum='Youreturnednull.Ifyoureffectdoesnotrequireclean'+'up,returnundefined(ornothing).';}elseif(typeofdestroy.then==='function'){ addendum='\n\nItlookslikeyouwrote'+hookName+'(async()=>...)orreturnedaPromise.'+'Instead,writetheasyncfunctioninsideyoureffect'+'andcallitimmediately:\n\n'+hookName+'(()=>{ \n'+'asyncfunctionfetchData(){ \n'+'//Youcanawaithere\n'+'constresponse=awaitMyAPI.getData(someId);\n'+'//...\n'+'}\n'+'fetchData();\n'+"},[someId]);//Or[]ifeffectdoesn'tneedpropsorstate\n\n"+'LearnmoreaboutdatafetchingwithHooks:/post/