react源码合成事件深入解析

class FuckEvent extends React.PureComponent {
  state = {
    showBox: false
  }
  componentDidMount() {
    document.body.addEventListener('click', this.handleClickBody, false)
  }
  componentWillUnmount() {
    document.body.removeEventListener('click', this.handleClickBody, false)
  }
  handleClickBody = () => {
    this.setState({
      showBox: false
    })
  }
  handleClickButton = () => {
    this.setState({
      showBox: true
    })
  }
  render() {
    return (
      <div>
        <button onClick={this.handleClickButton}>点击我显示弹窗</button>
        {this.state.showBox && (          <div onClick={e => e.stopPropagation()}>我是弹窗</div>
        )}      </div>
    )
  }
}

{
  this.state.showBox && <div onClick={e => e.stopPropagation()}>我是弹窗</div>
}

componentDidMount() {
  document.body.addEventListener('click', this.handleClickBody, false)
}
componentWillUnmount() {
  document.body.removeEventListener('click', this.handleClickBody, false)
}

/**
 * React和事件系统概述:
 *
 * +------------+    .
 * |    DOM     |    .
 * +------------+    .
 *       |           .
 *       v           .
 * +------------+    .
 * | ReactEvent |    .
 * |  Listener  |    .
 * +------------+    .                         +-----------+
 *       |           .               +--------+|SimpleEvent|
 *       |           .               |         |Plugin     |
 * +-----|------+    .               v         +-----------+
 * |     |      |    .    +--------------+                    +------------+
 * |     +-----------.--->|EventPluginHub|                    |    Event   |
 * |            |    .    |              |     +-----------+  | Propagators|
 * | ReactEvent |    .    |              |     |TapEvent   |  |------------|
 * |  Emitter   |    .    |              |<---+|Plugin     |  |other plugin|
 * |            |    .    |              |     +-----------+  |  utilities |
 * |     +-----------.--->|              |                    +------------+
 * |     |      |    .    +--------------+
 * +-----|------+    .                ^        +-----------+
 *       |           .                |        |Enter/Leave|
 *       +           .                +-------+|Plugin     |
 * +-------------+   .                         +-----------+
 * | application |   .
 * |-------------|   .
 * |             |   .
 * |             |   .
 * +-------------+   .
 *                   .
 */

class TaskEvent extends Reac.PureComponent {
  render() {
    return (
      <div
        onClick={() => {
          console.log('我是注册事件')
        }}
      >
        呵呵呵
      </div>
    )
  }
}

mountComponent: function(transaction, hostParent, hostContainerInfo, context) {
  // ...
  var props = this._currentElement.props;
  // ...
  this._updateDOMProperties(null, props, transaction);
  // ...
}

_updateDOMProperties: function (lastProps, nextProps, transaction) {
    // ...
    for (propKey in nextProps) {
      var nextProp = nextProps[propKey];
      var lastProp = propKey === STYLE ? this._previousStyleCopy : lastProps != null ? lastProps[propKey] : undefined;
      if (!nextProps.hasOwnProperty(propKey) || nextProp === lastProp || nextProp == null && lastProp == null) {
        continue;
      }
      if (propKey === STYLE) {
        // ...
      } else if (registrationNameModules.hasOwnProperty(propKey)) {
        // 如果是props这个对象直接声明的属性，而不是从原型链中继承而来的，则处理它
        // 对于mountComponent，lastProp为null。updateComponent二者都不为null。unmountComponent则nextProp为null
        if (nextProp) {
          // mountComponent和updateComponent中，enqueuePutListener注册事件
          enqueuePutListener(this, propKey, nextProp, transaction);
        } else if (lastProp) {
          // unmountComponent中，删除注册的listener，防止内存泄漏
          deleteListener(this, propKey);
        }
      }
    }
}

function enqueuePutListener(inst, registrationName, listener, transaction) {
  if (transaction instanceof ReactServerRenderingTransaction) {
    return
  }
  var containerInfo = inst._hostContainerInfo
  var isDocumentFragment =
    containerInfo._node && containerInfo._node.nodeType === DOC_FRAGMENT_TYPE
  // 找到document
  var doc = isDocumentFragment
    ? containerInfo._node
    : containerInfo._ownerDocument
  // 注册事件，将事件注册到document上
  listenTo(registrationName, doc)
  // 存储事件,放入事务队列中
  transaction.getReactMountReady().enqueue(putListener, {
    inst: inst,
    registrationName: registrationName,
    listener: listener
  })
}

export function listenTo(
  registrationName: string,
  mountAt: Document | Element | Node
): void {
  const listeningSet = getListeningSetForElement(mountAt)
  const dependencies = registrationNameDependencies[registrationName]
  for (let i = 0; i < dependencies.length; i++) {
    const dependency = dependencies[i]
    // 调用该方法进行注册
    listenToTopLevel(dependency, mountAt, listeningSet)
  }
}

export function listenToTopLevel(
  topLevelType: DOMTopLevelEventType,
  mountAt: Document | Element | Node,
  listeningSet: Set<DOMTopLevelEventType | string>
): void {
  if (!listeningSet.has(topLevelType)) {
    switch (topLevelType) {
      //...
      case TOP_CANCEL:
      case TOP_CLOSE:
        if (isEventSupported(getRawEventName(topLevelType))) {
          trapCapturedEvent(topLevelType, mountAt) // 捕获阶段
        }
        break
      default:
        const isMediaEvent = mediaEventTypes.indexOf(topLevelType) !== -1
        if (!isMediaEvent) {
          trapBubbledEvent(topLevelType, mountAt) // 冒泡阶段
        }
        break
    }
    listeningSet.add(topLevelType)
  }
}

// 捕获阶段
export function trapCapturedEvent(
  topLevelType: DOMTopLevelEventType,  element: Document | Element | Node
): void {
  trapEventForPluginEventSystem(element, topLevelType, true)
}
// 冒泡阶段
export function trapBubbledEvent(
  topLevelType: DOMTopLevelEventType,  element: Document | Element | Node
): void {
  trapEventForPluginEventSystem(element, topLevelType, false)
}

function trapEventForPluginEventSystem(
  element: Document | Element | Node,
  topLevelType: DOMTopLevelEventType,
  capture: boolean // 决定捕获还是冒泡阶段
): void {
  let listener
  switch (getEventPriority(topLevelType)) {
  }
  const rawEventName = getRawEventName(topLevelType)
  if (capture) {
    addEventCaptureListener(element, rawEventName, listener)
  } else {
    addEventBubbleListener(element, rawEventName, listener)
  }
}

// 捕获
export function addEventCaptureListener(
  element: Document | Element | Node,  eventType: string,  listener: Function
): void {
  element.addEventListener(eventType, listener, true)
}
// 冒泡
export function addEventBubbleListener(
  element: Document | Element | Node,  eventType: string,  listener: Function
): void {
  element.addEventListener(eventType, listener, false)
}

function enqueuePutListener(inst, registrationName, listener, transaction) {
  //...
  // 注册事件，将事件注册到document上
  listenTo(registrationName, doc)
  // 存储事件,放入事务队列中
  transaction.getReactMountReady().enqueue(putListener, {
    inst: inst,
    registrationName: registrationName,
    listener: listener
  })
}

putListener: function (inst, registrationName, listener) {
  // 用来标识注册了事件,比如onClick的React对象。key的格式为'.nodeId', 只用知道它可以标示哪个React对象就可以了
  // step1: 得到组件唯一标识
  var key = getDictionaryKey(inst);
  // step2: 得到listenerBank对象中指定事件类型的对象
  var bankForRegistrationName = listenerBank[registrationName] || (listenerBank[registrationName] = {});
  // step3: 将listener事件回调方法存入listenerBank[registrationName][key]中,比如listenerBank['onclick'][nodeId]
  // 所有React组件对象定义的所有React事件都会存储在listenerBank中
  bankForRegistrationName[key] = listener;
  // ...
}
// 拿到组件唯一标识
var getDictionaryKey = function (inst) {
  return '.' + inst._rootNodeID;
};

// 源码看这里: https://github.com/facebook/react/blob/master/packages/react-dom/src/events/ReactDOMEventListener.js#L419
const nativeEventTarget = getEventTarget(nativeEvent)
let targetInst = getClosestInstanceFromNode(nativeEventTarget)

function getEventTarget(nativeEvent) {
  let target = nativeEvent.target || nativeEvent.srcElement || window
  if (target.correspondingUseElement) {
    target = target.correspondingUseElement
  }
  return target.nodeType === TEXT_NODE ? target.parentNode : target
}

function dispatchEventForPluginEventSystem(
  topLevelType: DOMTopLevelEventType,
  eventSystemFlags: EventSystemFlags,
  nativeEvent: AnyNativeEvent,
  targetInst: null | Fiber
): void {
  const bookKeeping = getTopLevelCallbackBookKeeping(
    topLevelType,
    nativeEvent,
    targetInst,
    eventSystemFlags
  )
  try {
    // Event queue being processed in the same cycle allows
    // `preventDefault`.
    batchedEventUpdates(handleTopLevel, bookKeeping)
  } finally {
    releaseTopLevelCallbackBookKeeping(bookKeeping)
  }
}

function handleTopLevel(bookKeeping: BookKeepingInstance) {
  let targetInst = bookKeeping.targetInst
  // Loop through the hierarchy, in case there's any nested components.
  // It's important that we build the array of ancestors before calling any
  // event handlers, because event handlers can modify the DOM, leading to
  // inconsistencies with ReactMount's node cache. See #1105.
  let ancestor = targetInst
  do {
    if (!ancestor) {
      const ancestors = bookKeeping.ancestors
      ;((ancestors: any): Array<Fiber | null>).push(ancestor)
      break
    }
    const root = findRootContainerNode(ancestor)
    if (!root) {
      break
    }
    const tag = ancestor.tag
    if (tag === HostComponent || tag === HostText) {
      bookKeeping.ancestors.push(ancestor)
    }
    ancestor = getClosestInstanceFromNode(root)
  } while (ancestor)
}

for (let i = 0; i < bookKeeping.ancestors.length; i++) {
  targetInst = bookKeeping.ancestors[i]
  // getEventTarget上边有讲到
  const eventTarget = getEventTarget(bookKeeping.nativeEvent)
  const topLevelType = ((bookKeeping.topLevelType: any): DOMTopLevelEventType)
  const nativeEvent = ((bookKeeping.nativeEvent: any): AnyNativeEvent)
  runExtractedPluginEventsInBatch(
    topLevelType,
    targetInst,
    nativeEvent,
    eventTarget,
    bookKeeping.eventSystemFlags
  )
}

export function runExtractedPluginEventsInBatch(
  topLevelType: TopLevelType,
  targetInst: null | Fiber,
  nativeEvent: AnyNativeEvent,
  nativeEventTarget: EventTarget,
  eventSystemFlags: EventSystemFlags
) {
  // step1 : 构造合成事件
  const events = extractPluginEvents(
    topLevelType,
    targetInst,
    nativeEvent,
    nativeEventTarget,
    eventSystemFlags
  )
  // step2 : 批处理
  runEventsInBatch(events)
}

function extractPluginEvents(
  topLevelType: TopLevelType,  targetInst: null | Fiber,  nativeEvent: AnyNativeEvent,  nativeEventTarget: EventTarget,  eventSystemFlags: EventSystemFlags
): Array<ReactSyntheticEvent> | ReactSyntheticEvent | null {
  let events = null
  for (let i = 0; i < plugins.length; i++) {
    // Not every plugin in the ordering may be loaded at runtime.
    const possiblePlugin: PluginModule<AnyNativeEvent> = plugins[i]
    if (possiblePlugin) {
      const extractedEvents = possiblePlugin.extractEvents(
        topLevelType,
        targetInst,
        nativeEvent,
        nativeEventTarget,
        eventSystemFlags
      )
      if (extractedEvents) {
        events = accumulateInto(events, extractedEvents)
      }
    }
  }
  return events
}

// 📢 源码地址 : https://github.com/facebook/react/blob/master/packages/legacy-events/EventPluginHub.js#L80
export const injection = {
  injectEventPluginOrder,
  injectEventPluginsByName
}

// 📢 源码地址 : https://github.com/facebook/react/blob/master/packages/react-dom/src/client/ReactDOMClientInjection.js#L26
EventPluginHubInjection.injectEventPluginOrder(DOMEventPluginOrder)
EventPluginHubInjection.injectEventPluginsByName({
  SimpleEventPlugin: SimpleEventPlugin,
  EnterLeaveEventPlugin: EnterLeaveEventPlugin,
  ChangeEventPlugin: ChangeEventPlugin,
  SelectEventPlugin: SelectEventPlugin,
  BeforeInputEventPlugin: BeforeInputEventPlugin
})

const extractedEvents = possiblePlugin.extractEvents(
  topLevelType,
  targetInst,
  nativeEvent,
  nativeEventTarget,
  eventSystemFlags
)
if (extractedEvents) {
  events = accumulateInto(events, extractedEvents)
}

extractEvents: function() {
  const dispatchConfig = topLevelEventsToDispatchConfig[topLevelType]
  if (!dispatchConfig) {
    return null
  }
  //...
}

extractEvents: function() {
  //...
  let EventConstructor
  switch (topLevelType) {
    // ...
    case DOMTopLevelEventTypes.TOP_POINTER_UP:
      EventConstructor = SyntheticPointerEvent
      break
    default:
      EventConstructor = SyntheticEvent
      break
  }
}

extractEvents: function() {
  //...
  const event = EventConstructor.getPooled(
    dispatchConfig,
    targetInst,
    nativeEvent,
    nativeEventTarget
  )
  accumulateTwoPhaseDispatches(event)
  return event
}

function addEventPoolingTo(EventConstructor) {
  EventConstructor.eventPool = []
  // 就是这里设置了getPooled
  EventConstructor.getPooled = getPooledEvent
  EventConstructor.release = releasePooledEvent
}
SyntheticEvent.extend = function(Interface) {
  //...
  addEventPoolingTo(Class)
  return Class
}
addEventPoolingTo(SyntheticEvent)

function getPooledEvent(dispatchConfig, targetInst, nativeEvent, nativeInst) {
  const EventConstructor = this
  if (EventConstructor.eventPool.length) {
    const instance = EventConstructor.eventPool.pop()
    EventConstructor.call(
      instance,
      dispatchConfig,
      targetInst,
      nativeEvent,
      nativeInst
    )
    return instance
  }
  return new EventConstructor(
    dispatchConfig,
    targetInst,
    nativeEvent,
    nativeInst
  )
}

export function runEventsInBatch(
  events: Array<ReactSyntheticEvent> | ReactSyntheticEvent | null
) {
  if (events !== null) {
    eventQueue = accumulateInto(eventQueue, events)
  }
  // Set `eventQueue` to null before processing it so that we can tell if more
  // events get enqueued while processing.
  const processingEventQueue = eventQueue
  eventQueue = null
  if (!processingEventQueue) {
    return
  }
  forEachAccumulated(processingEventQueue, executeDispatchesAndReleaseTopLevel)
  invariant(
    !eventQueue,
    'processEventQueue(): Additional events were enqueued while processing ' +
      'an event queue. Support for this has not yet been implemented.'
  )
  // This would be a good time to rethrow if any of the event handlers threw.
  rethrowCaughtError()
}

function forEachAccumulated<T>(
  arr: ?(Array<T> | T),
  cb: (elem: T) => void,
  scope: ?any
) {
  if (Array.isArray(arr)) {
    arr.forEach(cb, scope)
  } else if (arr) {
    cb.call(scope, arr)
  }
}

const executeDispatchesAndRelease = function(event: ReactSyntheticEvent) {
  if (event) {
    executeDispatchesInOrder(event)
    if (!event.isPersistent()) {
      event.constructor.release(event)
    }
  }
}
const executeDispatchesAndReleaseTopLevel = function(e) {
  return executeDispatchesAndRelease(e)
}

export function executeDispatchesInOrder(event) {
  const dispatchListeners = event._dispatchListeners
  const dispatchInstances = event._dispatchInstances  if (__DEV__) {
    validateEventDispatches(event)
  }
  if (Array.isArray(dispatchListeners)) {
    for (let i = 0; i < dispatchListeners.length; i++) {
      if (event.isPropagationStopped()) {
        break
      }
      // Listeners and Instances are two parallel arrays that are always in sync.
      executeDispatch(event, dispatchListeners[i], dispatchInstances[i])
    }
  } else if (dispatchListeners) {
    executeDispatch(event, dispatchListeners, dispatchInstances)
  }
  event._dispatchListeners = null
  event._dispatchInstances = null
}