这一章节就来讲讲ReactDOM.render()
方法的内部实现与流程吧。
因为初始化的源码文件部分所涵盖的内容很多,包括创建渲染
、更新渲染
、Fiber树
的创建与diff
,element
的创建与插入,还包括一些优化算法,所以我就整个的React
执行流程画了一个简单的示意图。
React源码执行流程图
从图中我们很清晰的看到ReactDOM.render()
之后我们的组件具体干了什么事情,那么我们进入源码文件一探究竟吧。
// packages/react-dom/src/client/ReactDOMLegacy.js export function render( element: React$Element<any>, // 经过babel解析后的element container: Container, // 根组件节点: document.getElementById('root').. callback: ?Function,// 回调 ) { // 做合法容器的验证(根组件) invariant( isValidContainer(container), 'Target container is not a DOM element.', ); // 开发模式下 if (__DEV__) { const isModernRoot = isContainerMarkedAsRoot(container) && container._reactRootContainer === undefined; if (isModernRoot) { console.error( 'You are calling ReactDOM.render() on a container that was previously ' + 'passed to ReactDOM.createRoot(). This is not supported. ' + 'Did you mean to call root.render(element)?', ); } } // 返回 legacyRenderSubtreeIntoContainer return legacyRenderSubtreeIntoContainer( null, element, container, false, callback, ); }
所以当前render
函数仅仅只是做了部分逻辑,阅读React
源码,给你一个直观的感受就是他拆分的颗粒度非常的细,很多重复命名的函数,可能是见名知意的变量名只有那么几个常见的组合吧,这也是React作者的用心良苦吧。
追根究底我们还是得看一看legacyRenderSubtreeIntoContainer
究竟干了些不为人知的事情呢
legacyRenderSubtreeIntoContainer
function legacyRenderSubtreeIntoContainer( parentComponent: ?React$Component<any, any>, // 父级组件 children: ReactNodeList, // 当前元素 container: Container, // 容器 eg:getElementById('root') forceHydrate: boolean, callback: ?Function, ) { if (__DEV__) { topLevelUpdateWarnings(container); warnOnInvalidCallback(callback === undefined ? null : callback, 'render'); } // TODO: Without `any` type, Flow says "Property cannot be accessed on any // member of intersection type." Whyyyyyy. let root: RootType = (container._reactRootContainer: any); let fiberRoot; // 如果有根组件,表示不是初始化渲染,则走下面的批量更新 // 没有根组件,那么就要去创建根组件了 if (!root) { // 初始化挂载 root = container._reactRootContainer = legacyCreateRootFromDOMContainer( container, forceHydrate, ); fiberRoot = root._internalRoot; if (typeof callback === 'function') { const originalCallback = callback; callback = function() { const instance = getPublicRootInstance(fiberRoot); originalCallback.call(instance); }; } // 不必要的批量更新 unbatchedUpdates(() => { updateContainer(children, fiberRoot, parentComponent, callback); }); } else { fiberRoot = root._internalRoot; if (typeof callback === 'function') { const originalCallback = callback; callback = function() { const instance = getPublicRootInstance(fiberRoot); originalCallback.call(instance); }; } // 批量更新 updateContainer(children, fiberRoot, parentComponent, callback); } return getPublicRootInstance(fiberRoot); }
- 有根节点的情况下,我们判定为非首次渲染状态,执行
updateContainer
- 没有根节点的情况下,我们判定为首次渲染,接着去创建根节点,执行
legacyCreateRootFromDOMContainer
,拿到了root
之后,我们会去触发执行updateContainer
legacyCreateRootFromDOMContainer
function legacyCreateRootFromDOMContainer( container: Container, // 容器 forceHydrate: boolean, // value:false ): RootType { const shouldHydrate = forceHydrate || shouldHydrateDueToLegacyHeuristic(container); // First clear any existing content. if (!shouldHydrate) { let warned = false; let rootSibling; while ((rootSibling = container.lastChild)) { if (__DEV__) { if ( !warned && rootSibling.nodeType === ELEMENT_NODE && (rootSibling: any).hasAttribute(ROOT_ATTRIBUTE_NAME) ) { warned = true; console.error( 'render(): Target node has markup rendered by React, but there ' + 'are unrelated nodes as well. This is most commonly caused by ' + 'white-space inserted around server-rendered markup.', ); } } container.removeChild(rootSibling); } } if (__DEV__) { if (shouldHydrate && !forceHydrate && !warnedAboutHydrateAPI) { warnedAboutHydrateAPI = true; console.warn( 'render(): Calling ReactDOM.render() to hydrate server-rendered markup ' + 'will stop working in React v18. Replace the ReactDOM.render() call ' + 'with ReactDOM.hydrate() if you want React to attach to the server HTML.', ); } } // 关注createLegacyRoot return createLegacyRoot( container, shouldHydrate ? { hydrate: true, } : undefined, ); }
createLegacyRoot
export function createLegacyRoot( container: Container, // 容器 options?: RootOptions, ): RootType { //关注ReactDOMBlockingRoot return new ReactDOMBlockingRoot(container, LegacyRoot, options); }
ReactDOMBlockingRoot
function ReactDOMBlockingRoot( container: Container, // 容器 tag: RootTag, // LegacyRoot = 0;BlockingRoot = 1;ConcurrentRoot = 2; options: void | RootOptions, ) { this._internalRoot = createRootImpl(container, tag, options); }
- 我们在这里看到
this._internalRoot
出来了,因为在先前这个值会给到fiberRoot
,所以我们再去看一看这个_internalRoot
是怎么创建出来的 - 相关参考视频讲解:进入学习
createRootImpl
function createRootImpl( container: Container, tag: RootTag, options: void | RootOptions, ) { // Tag is either LegacyRoot or Concurrent Root const hydrate = options != null && options.hydrate === true; const hydrationCallbacks = (options != null && options.hydrationOptions) || null; const mutableSources = (options != null && options.hydrationOptions != null && options.hydrationOptions.mutableSources) || null; // 关注createContainer const root = createContainer(container, tag, hydrate, hydrationCallbacks); markContainerAsRoot(root.current, container); const containerNodeType = container.nodeType; if (enableEagerRootListeners) { const rootContainerElement = container.nodeType === COMMENT_NODE ? container.parentNode : container; listenToAllSupportedEvents(rootContainerElement); } else { if (hydrate && tag !== LegacyRoot) { const doc = containerNodeType === DOCUMENT_NODE ? container : container.ownerDocument; // We need to cast this because Flow doesn't work // with the hoisted containerNodeType. If we inline // it, then Flow doesn't complain. We intentionally // hoist it to reduce code-size. eagerlyTrapReplayableEvents(container, ((doc: any): Document)); } else if ( containerNodeType !== DOCUMENT_FRAGMENT_NODE && containerNodeType !== DOCUMENT_NODE ) { ensureListeningTo(container, 'onMouseEnter', null); } } if (mutableSources) { for (let i = 0; i < mutableSources.length; i++) { const mutableSource = mutableSources[i]; registerMutableSourceForHydration(root, mutableSource); } } // 关注root return root; }
见名知意关注createContainer
为创建容器,看其源码
createContainer
// packages/react-reconciler/src/ReactFiberReconciler.old.js export function createContainer( containerInfo: Container, // 容器 tag: RootTag, // LegacyRoot = 0;BlockingRoot = 1;ConcurrentRoot = 2; hydrate: boolean, hydrationCallbacks: null | SuspenseHydrationCallbacks, ): OpaqueRoot { // 关注createFiberRoot return createFiberRoot(containerInfo, tag, hydrate, hydrationCallbacks); }
createFiberRoot
export function createFiberRoot( containerInfo: any, tag: RootTag, hydrate: boolean, hydrationCallbacks: null | SuspenseHydrationCallbacks, ): FiberRoot { const root: FiberRoot = (new FiberRootNode(containerInfo, tag, hydrate): any); if (enableSuspenseCallback) { root.hydrationCallbacks = hydrationCallbacks; } // 关注createHostRootFiber const uninitializedFiber = createHostRootFiber(tag); root.current = uninitializedFiber; uninitializedFiber.stateNode = root; // 初始化更新队列 initializeUpdateQueue(uninitializedFiber); return root; }
关注 root.current
、uninitializedFiber.stateNode
这两个玩意儿,后面有大作用,我们还是看看createHostRootFiber
吧
createHostRootFiber
export function createHostRootFiber(tag: RootTag): Fiber { let mode; if (tag === ConcurrentRoot) { mode = ConcurrentMode | BlockingMode | StrictMode; } else if (tag === BlockingRoot) { mode = BlockingMode | StrictMode; } else { mode = NoMode; } if (enableProfilerTimer && isDevToolsPresent) { // Always collect profile timings when DevTools are present. // This enables DevTools to start capturing timing at any point– // Without some nodes in the tree having empty base times. mode |= ProfileMode; } return createFiber(HostRoot, null, null, mode); }
一眼望去这里便是对tag
的处理,到了后面便是去创建fiber
节点
createFiber
const createFiber = function( tag: WorkTag, pendingProps: mixed, key: null | string, mode: TypeOfMode, ): Fiber { // $FlowFixMe: the shapes are exact here but Flow doesn't like constructors return new FiberNode(tag, pendingProps, key, mode); };
那么主角出来了,就是我们的FiberNode
,这里才走完初始化的创建流程,
所以大致的流程就是上面的图里画的那样子,创建流程我们就告一段落,那我们再去看看更新的流程是怎么玩的。
我们知道除了ReactDOM.render()
会触发更新流程之外,我们还有setState
、强制更新
、hooks
里面的setXxxx
等等手段可以触发更新,所谓setState
那么不正好是我们Component
原型上挂的方法嘛。我们回顾一下Component,那些更新都是调用了updater触发器上的方法,那么我们去看一下这个东西。
const classComponentUpdater = { isMounted, // setState enqueueSetState(inst, payload, callback) { const fiber = getInstance(inst); const eventTime = requestEventTime(); // 获取更新触发的时间 const lane = requestUpdateLane(fiber); // 获取任务优先级 //根据更新触发时间 + 更新优先级来创建更新任务对象 const update = createUpdate(eventTime, lane); // 创建更新任务对象 // const update: Update<*> = { // eventTime, // 更新时间 // lane, // 优先级 // tag: UpdateState, // 更新类型:0更新,1替换。,2强制替换,3捕获型更新 // payload: null,// 需要更新的内容 // callback: null, // 更新完后的回调 // next: null, // 指向下一个更新 // }; // 把内容填上 update.payload = payload; if (callback !== undefined && callback !== null) { if (__DEV__) { // 开发环境下腰给个警告 warnOnInvalidCallback(callback, 'setState'); } // 如果有回调,那么加上回调 update.callback = callback; } // const update: Update<*> = { // eventTime, // 更新时间 you // lane, // 优先级 you // tag: UpdateState, // 更新类型:0更新,1替换。,2强制替换,3捕获型更新 // payload: null,// 需要更新的内容 you // callback: null, // 更新完后的回调 you // next: null, // 指向下一个更新 // }; enqueueUpdate(fiber, update);// 推入更新队列 scheduleUpdateOnFiber(fiber, lane, eventTime);// 调度 if (__DEV__) { if (enableDebugTracing) { if (fiber.mode & DebugTracingMode) { const name = getComponentName(fiber.type) || 'Unknown'; logStateUpdateScheduled(name, lane, payload); } } } if (enableSchedulingProfiler) { markStateUpdateScheduled(fiber, lane); } }, // replaceState enqueueReplaceState(inst, payload, callback) { const fiber = getInstance(inst); const eventTime = requestEventTime(); const lane = requestUpdateLane(fiber); const update = createUpdate(eventTime, lane); update.tag = ReplaceState; update.payload = payload; if (callback !== undefined && callback !== null) { if (__DEV__) { warnOnInvalidCallback(callback, 'replaceState'); } update.callback = callback; } enqueueUpdate(fiber, update); scheduleUpdateOnFiber(fiber, lane, eventTime); if (__DEV__) { if (enableDebugTracing) { if (fiber.mode & DebugTracingMode) { const name = getComponentName(fiber.type) || 'Unknown'; logStateUpdateScheduled(name, lane, payload); } } } if (enableSchedulingProfiler) { markStateUpdateScheduled(fiber, lane); } }, // forceUpdate enqueueForceUpdate(inst, callback) { const fiber = getInstance(inst); const eventTime = requestEventTime(); const lane = requestUpdateLane(fiber); const update = createUpdate(eventTime, lane); update.tag = ForceUpdate; if (callback !== undefined && callback !== null) { if (__DEV__) { warnOnInvalidCallback(callback, 'forceUpdate'); } update.callback = callback; } enqueueUpdate(fiber, update); scheduleUpdateOnFiber(fiber, lane, eventTime); if (__DEV__) { if (enableDebugTracing) { if (fiber.mode & DebugTracingMode) { const name = getComponentName(fiber.type) || 'Unknown'; logForceUpdateScheduled(name, lane); } } } if (enableSchedulingProfiler) { markForceUpdateScheduled(fiber, lane); } }, };
updateContainer
export function updateContainer( element: ReactNodeList, container: OpaqueRoot, parentComponent: ?React$Component<any, any>, callback: ?Function, ): Lane { if (__DEV__) { onScheduleRoot(container, element); } const current = container.current; const eventTime = requestEventTime(); if (__DEV__) { // $FlowExpectedError - jest isn't a global, and isn't recognized outside of tests if ('undefined' !== typeof jest) { warnIfUnmockedScheduler(current); warnIfNotScopedWithMatchingAct(current); } } const lane = requestUpdateLane(current); if (enableSchedulingProfiler) { markRenderScheduled(lane); } const context = getContextForSubtree(parentComponent); if (container.context === null) { container.context = context; } else { container.pendingContext = context; } if (__DEV__) { if ( ReactCurrentFiberIsRendering && ReactCurrentFiberCurrent !== null && !didWarnAboutNestedUpdates ) { didWarnAboutNestedUpdates = true; console.error( 'Render methods should be a pure function of props and state; ' + 'triggering nested component updates from render is not allowed. ' + 'If necessary, trigger nested updates in componentDidUpdate.\n\n' + 'Check the render method of %s.', getComponentName(ReactCurrentFiberCurrent.type) || 'Unknown', ); } } const update = createUpdate(eventTime, lane);// 创建更新任务 // Caution: React DevTools currently depends on this property // being called "element". update.payload = {element}; callback = callback === undefined ? null : callback; if (callback !== null) { if (__DEV__) { if (typeof callback !== 'function') { console.error( 'render(...): Expected the last optional `callback` argument to be a ' + 'function. Instead received: %s.', callback, ); } } update.callback = callback; } enqueueUpdate(current, update); // 推入更新队列 scheduleUpdateOnFiber(current, lane, eventTime); // 进行调度 return lane; }
我们看到了enqueueSetState
、enqueueReplaceState
、enqueueForceUpdate
还是初始化时候走的updateContainer
都是走了几乎一样的逻辑:requestEventTime
=> requestUpdateLane
=> createUpdate
=> enqueueUpdate
=> scheduleUpdateOnFiber
总结
本章从ReactDOM.render()
开始讲解了,初始化的时候,根节点的创建与更新流程,以及在类组件原型上挂载的一些更新的方法,但是为什么这一章不直接把他更新流程讲完呢?因为下一章要讲一下fiberNode
这个东西,简而言之他只是一个架构概念,并不是React
独有的,但是现在很有必要一起来看一看这个,那么下一章我们来一起揭开FiberNode
的神秘面纱吧
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