react组件的创建与更新实现流程详解
作者：flyzz177
React组件分为函数组件与class组件；函数组件是无状态组件，class称为类组件；函数组件只有props，没有自己的私有数据和生命周期函数；class组件有自己私有数据(this.state)和生命周期函数
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
到此这篇关于react组件的创建与更新实现流程详解的文章就介绍到这了,更多相关react组件的创建与更新内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！