// packages/react-dom/src/events/DOMPluginEventSystem.js
export function listenToAllSupportedEvents(rootContainerElement: EventTarget) {
  if (enableEagerRootListeners) { // enableEagerRootListeners默認(rèn)值為false
    // listeningMarker就是一個隨機(jī)數(shù)+字符串，作為唯一值
    if (rootContainerElement[listeningMarker]) {
      ...
      return;
    }
    rootContainerElement[listeningMarker] = true;
    // 遍歷allNativeEvents的所有事件
    allNativeEvents.forEach(domEventName => {
      // 如果不是委托事件，沒有冒泡階段
      // nonDelegatedEvents全部媒體事件，
      if (!nonDelegatedEvents.has(domEventName)) {
        listenToNativeEvent(
          domEventName,
          false,
          ((rootContainerElement: any): Element),
          null,
        );
      }
      // 有冒泡階段
      listenToNativeEvent(
        domEventName,
        true,
        ((rootContainerElement: any): Element),
        null,
      );
    });
  }
}
//listeningMarker
// 唯一標(biāo)識
const listeningMarker =
  '_reactListening' +
  Math.random()
    .toString(36)
    .slice(2);

export const allNativeEvents: Set<DOMEventName> = new Set();

export function listenToNativeEvent(
  domEventName: DOMEventName,// 事件名
  isCapturePhaseListener: boolean, // 根據(jù)上個函數(shù)，這里應(yīng)該是確定是是能夠冒泡的事件
  rootContainerElement: EventTarget,  targetElement: Element | null,  eventSystemFlags?: EventSystemFlags = 0, // 事件標(biāo)記
): void {
  let target = rootContainerElement;
  //如果是selectionchange事件，加到dom上
  if (
    domEventName === 'selectionchange' &&
    (rootContainerElement: any).nodeType !== DOCUMENT_NODE
  ) {
    target = (rootContainerElement: any).ownerDocument;
  }
  if (
    targetElement !== null &&
    !isCapturePhaseListener &&
    nonDelegatedEvents.has(domEventName) // 非冒泡事件
  ) {
   ...
    //滾動事件不冒泡
    if (domEventName !== 'scroll') {
      return;
    }
    eventSystemFlags |= IS_NON_DELEGATED; // is_non_delegated 不是委托事件
    target = targetElement;
  }
  //獲取dom上綁定的事件名數(shù)組 Set[] || 
  const listenerSet = getEventListenerSet(target);
  // 處理事件名為捕獲階段與冒泡階段 Set[click_bubble]
  const listenerSetKey = getListenerSetKey(
    domEventName,
    isCapturePhaseListener,
  );
  // 把沒有打過的IS_CAPTURE_PHASE的符合條件的事件，打上標(biāo)簽
  if (!listenerSet.has(listenerSetKey)) {
    if (isCapturePhaseListener) {
      // 打上捕獲的標(biāo)簽
      eventSystemFlags |= IS_CAPTURE_PHASE;
    }
    // 往節(jié)點(diǎn)上添加事件綁定
    addTrappedEventListener(
      target,
      domEventName,
      eventSystemFlags,
      isCapturePhaseListener,
    );
    // 往listenerSet中添加事件名
    listenerSet.add(listenerSetKey);
  }
}
//getEventListenerSet
export function getEventListenerSet(node: EventTarget): Set<string> {
  let elementListenerSet = (node: any)[internalEventHandlersKey];
  if (elementListenerSet === undefined) {
    // 創(chuàng)建一個Set來存放事件名
    elementListenerSet = (node: any)[internalEventHandlersKey] = new Set();
  }
  return elementListenerSet;
}
// getListenerSetKey
export function getListenerSetKey(
  domEventName: DOMEventName,  capture: boolean,
): string {
  // capture捕獲，bubble冒泡
  return `${domEventName}__${capture ? 'capture' : 'bubble'}`;
}
// addTrappedEventListener
function addTrappedEventListener(
  targetContainer: EventTarget, // 容器
  domEventName: DOMEventName, // 事件名
  eventSystemFlags: EventSystemFlags, //事件名標(biāo)識
  isCapturePhaseListener: boolean, // 事件委托
  isDeferredListenerForLegacyFBSupport?: boolean, 
) {
  // 創(chuàng)建具有優(yōu)先級的事件監(jiān)聽函數(shù)，返回值為function
  let listener = createEventListenerWrapperWithPriority(
    targetContainer,
    domEventName,
    eventSystemFlags,
  );
  ...
  targetContainer =
    enableLegacyFBSupport && isDeferredListenerForLegacyFBSupport
      ? (targetContainer: any).ownerDocument
      : targetContainer;
  let unsubscribeListener;
  ...
  // 區(qū)分捕獲、冒泡 通過node.addEventListener綁定事件到節(jié)點(diǎn)上
  if (isCapturePhaseListener) {
    if (isPassiveListener !== undefined) {
      unsubscribeListener = addEventCaptureListenerWithPassiveFlag(
        targetContainer,
        domEventName,
        listener,
        isPassiveListener,
      );
    } else {
      unsubscribeListener = addEventCaptureListener(
        targetContainer,
        domEventName,
        listener,
      );
    }
  } else {
    if (isPassiveListener !== undefined) {
      unsubscribeListener = addEventBubbleListenerWithPassiveFlag(
        targetContainer,
        domEventName,
        listener,
        isPassiveListener,
      );
    } else {
      unsubscribeListener = addEventBubbleListener(
        targetContainer,
        domEventName,
        listener,
      );
    }
  }
}
// createEventListenerWrapperWithPriority
export function createEventListenerWrapperWithPriority(
  targetContainer: EventTarget, // 容器
  domEventName: DOMEventName, // 事件名
  eventSystemFlags: EventSystemFlags, //標(biāo)識
): Function {
  // 獲取事件Map里面已經(jīng)標(biāo)記好的優(yōu)先級
  const eventPriority = getEventPriorityForPluginSystem(domEventName);
  let listenerWrapper;
  // 根據(jù)優(yōu)先級不同綁定不同的執(zhí)行函數(shù)
  switch (eventPriority) {
    //離散事件
    case DiscreteEvent:
      listenerWrapper = dispatchDiscreteEvent;
      break;
    // 用戶交互阻塞渲染的事件 
    case UserBlockingEvent:
      listenerWrapper = dispatchUserBlockingUpdate;
      break;
    // 其他事件
    case ContinuousEvent:
    // 默認(rèn)事件
    default:
      listenerWrapper = dispatchEvent;
      break;
  }
  return listenerWrapper.bind(
    null,
    domEventName,
    eventSystemFlags,
    targetContainer,
  );
}

export function getEventPriorityForPluginSystem(
  domEventName: DOMEventName,
): EventPriority {
  // 通過事件名獲取優(yōu)先級
  const priority = eventPriorities.get(domEventName);
  // ContinuousEvent為默認(rèn)優(yōu)先級 
  return priority === undefined ? ContinuousEvent : priority;
}
//eventPriorities
const eventPriorities = new Map();

// packages/react-dom/src/events/DOMEventProperties.js
function setEventPriorities(
  eventTypes: Array<DOMEventName>,  priority: EventPriority,
): void {
  for (let i = 0; i < eventTypes.length; i++) {
    // 往eventPriorities添加優(yōu)先級
    eventPriorities.set(eventTypes[i], priority);
  }
}
//registerSimplePluginEventsAndSetTheirPriorities
function registerSimplePluginEventsAndSetTheirPriorities(
  eventTypes: Array<DOMEventName | string>,  priority: EventPriority,
): void {
  for (let i = 0; i < eventTypes.length; i += 2) {
    const topEvent = ((eventTypes[i]: any): DOMEventName);
    const event = ((eventTypes[i + 1]: any): string);
    const capitalizedEvent = event[0].toUpperCase() + event.slice(1);
    // 改變事件名 click => onClick
    const reactName = 'on' + capitalizedEvent;
    // 往eventPriorities添加優(yōu)先級
    eventPriorities.set(topEvent, priority);
    topLevelEventsToReactNames.set(topEvent, reactName);
    // 注冊捕獲階段，冒泡階段的事件
    registerTwoPhaseEvent(reactName, [topEvent]);
  }
}

// packages/react-dom/src/events/DOMEventProperties.js
export function registerSimpleEvents() {
  // 處理離散事件優(yōu)先級
  registerSimplePluginEventsAndSetTheirPriorities(
    discreteEventPairsForSimpleEventPlugin,
    DiscreteEvent,
  );
  // 處理用戶阻塞事件優(yōu)先級
  registerSimplePluginEventsAndSetTheirPriorities(
    userBlockingPairsForSimpleEventPlugin,
    UserBlockingEvent,
  );
  // 處理默認(rèn)事件優(yōu)先級
  registerSimplePluginEventsAndSetTheirPriorities(
    continuousPairsForSimpleEventPlugin,
    ContinuousEvent,
  );
  // 處理其他事件優(yōu)先級
  setEventPriorities(otherDiscreteEvents, DiscreteEvent);
}

const discreteEventPairsForSimpleEventPlugin = [
  ('cancel': DOMEventName), 'cancel',
  ('click': DOMEventName), 'click',
  ('close': DOMEventName), 'close',
  ('contextmenu': DOMEventName), 'contextMenu',
  ('copy': DOMEventName), 'copy',
  ('cut': DOMEventName), 'cut',
  ('auxclick': DOMEventName), 'auxClick',
  ('dblclick': DOMEventName), 'doubleClick', // Careful!
  ('dragend': DOMEventName), 'dragEnd',
  ('dragstart': DOMEventName), 'dragStart',
  ('drop': DOMEventName), 'drop',
  ('focusin': DOMEventName), 'focus', // Careful!
  ('focusout': DOMEventName), 'blur', // Careful!
  ('input': DOMEventName), 'input',
  ('invalid': DOMEventName), 'invalid',
  ('keydown': DOMEventName), 'keyDown',
  ('keypress': DOMEventName), 'keyPress',
  ('keyup': DOMEventName), 'keyUp',
  ('mousedown': DOMEventName), 'mouseDown',
  ('mouseup': DOMEventName), 'mouseUp',
  ('paste': DOMEventName), 'paste',
  ('pause': DOMEventName), 'pause',
  ('play': DOMEventName), 'play',
  ('pointercancel': DOMEventName), 'pointerCancel',
  ('pointerdown': DOMEventName), 'pointerDown',
  ('pointerup': DOMEventName), 'pointerUp',
  ('ratechange': DOMEventName), 'rateChange',
  ('reset': DOMEventName), 'reset',
  ('seeked': DOMEventName), 'seeked',
  ('submit': DOMEventName), 'submit',
  ('touchcancel': DOMEventName), 'touchCancel',
  ('touchend': DOMEventName), 'touchEnd',
  ('touchstart': DOMEventName), 'touchStart',
  ('volumechange': DOMEventName), 'volumeChange',
];
const otherDiscreteEvents: Array<DOMEventName> = [
  'change',
  'selectionchange',
  'textInput',
  'compositionstart',
  'compositionend',
  'compositionupdate',
];
const userBlockingPairsForSimpleEventPlugin: Array<string | DOMEventName> = [
  ('drag': DOMEventName), 'drag',
  ('dragenter': DOMEventName), 'dragEnter',
  ('dragexit': DOMEventName), 'dragExit',
  ('dragleave': DOMEventName), 'dragLeave',
  ('dragover': DOMEventName), 'dragOver',
  ('mousemove': DOMEventName), 'mouseMove',
  ('mouseout': DOMEventName), 'mouseOut',
  ('mouseover': DOMEventName), 'mouseOver',
  ('pointermove': DOMEventName), 'pointerMove',
  ('pointerout': DOMEventName), 'pointerOut',
  ('pointerover': DOMEventName), 'pointerOver',
  ('scroll': DOMEventName), 'scroll',
  ('toggle': DOMEventName), 'toggle',
  ('touchmove': DOMEventName), 'touchMove',
  ('wheel': DOMEventName), 'wheel',
];
const continuousPairsForSimpleEventPlugin: Array<string | DOMEventName> = [
  ('abort': DOMEventName), 'abort',
  (ANIMATION_END: DOMEventName), 'animationEnd',
  (ANIMATION_ITERATION: DOMEventName), 'animationIteration',
  (ANIMATION_START: DOMEventName), 'animationStart',
  ('canplay': DOMEventName), 'canPlay',
  ('canplaythrough': DOMEventName), 'canPlayThrough',
  ('durationchange': DOMEventName), 'durationChange',
  ('emptied': DOMEventName), 'emptied',
  ('encrypted': DOMEventName), 'encrypted',
  ('ended': DOMEventName), 'ended',
  ('error': DOMEventName), 'error',
  ('gotpointercapture': DOMEventName), 'gotPointerCapture',
  ('load': DOMEventName), 'load',
  ('loadeddata': DOMEventName), 'loadedData',
  ('loadedmetadata': DOMEventName), 'loadedMetadata',
  ('loadstart': DOMEventName), 'loadStart',
  ('lostpointercapture': DOMEventName), 'lostPointerCapture',
  ('playing': DOMEventName), 'playing',
  ('progress': DOMEventName), 'progress',
  ('seeking': DOMEventName), 'seeking',
  ('stalled': DOMEventName), 'stalled',
  ('suspend': DOMEventName), 'suspend',
  ('timeupdate': DOMEventName), 'timeUpdate',
  (TRANSITION_END: DOMEventName), 'transitionEnd',
  ('waiting': DOMEventName), 'waiting',
];

export function registerTwoPhaseEvent(
  registrationName: string, // 注冊事件reactName
  dependencies: Array<DOMEventName>, // 依賴
): void {
  registerDirectEvent(registrationName, dependencies);
  registerDirectEvent(registrationName + 'Capture', dependencies);
}

// Mapping from registration name to event name
export const registrationNameDependencies = {};
export function registerDirectEvent(
  registrationName: string, //react事件名onClick
  dependencies: Array<DOMEventName>, // 依賴
) {
  ...
  // 以react事件名為key，dependencies為value的map對象
  registrationNameDependencies[registrationName] = dependencies;
  if (__DEV__) {
    ...
  }
  // 遍歷依賴，把每一項(xiàng)加入到allNativeEvents中去
  for (let i = 0; i < dependencies.length; i++) {
    allNativeEvents.add(dependencies[i]);
  }
}

// packages/react-dom/src/events/ReactDOMEventListener.js
export function dispatchEvent(
  domEventName: DOMEventName, // 事件名
  eventSystemFlags: EventSystemFlags, // 事件類型標(biāo)記
  targetContainer: EventTarget, // 目標(biāo)容器
  nativeEvent: AnyNativeEvent, // native事件
): void {
  ...
  // 如果被阻塞了，嘗試調(diào)度事件 并返回掛載的實(shí)例或者容器
  const blockedOn = attemptToDispatchEvent(
    domEventName,
    eventSystemFlags,
    targetContainer,
    nativeEvent,
  );
  if (blockedOn === null) {
    // We successfully dispatched this event.
    ...
    return;
  }
  ...
  // 調(diào)度事件，觸發(fā)事件
  dispatchEventForPluginEventSystem(
    domEventName,
    eventSystemFlags,
    nativeEvent,
    null,
    targetContainer,
  );
}
// dispatchEventForPluginEventSystem
export function dispatchEventForPluginEventSystem(
  domEventName: DOMEventName,  eventSystemFlags: EventSystemFlags,  nativeEvent: AnyNativeEvent,  targetInst: null | Fiber,  targetContainer: EventTarget,
): void {
  ...
  //批量更新事件 
  batchedEventUpdates(() =>
    dispatchEventsForPlugins(
      domEventName,
      eventSystemFlags,
      nativeEvent,
      ancestorInst,
      targetContainer,
    ),
  );
}
// batchedEventUpdates
export function batchedEventUpdates(fn, a, b) {
  ...
  isBatchingEventUpdates = true;
  try {
    // fn : ()=>dispatchEventsForPlugins
    //(domEventName,eventSystemFlags,ativeEvent,ancestorInst,targetContainer,),
    // a: undefined
    // b: undefined
    return batchedEventUpdatesImpl(fn, a, b); 
    // batchedEventUpdatesImpl(fn, a, b) =>
    // Defaults
    // let batchedUpdatesImpl = function(fn, bookkeeping) {
    // return fn(bookkeeping); 執(zhí)行dispatchEventsForPlugins
};
  } finally {
    ...
  }
}

function dispatchEventsForPlugins(
  domEventName: DOMEventName,  eventSystemFlags: EventSystemFlags,  nativeEvent: AnyNativeEvent,  targetInst: null | Fiber,  targetContainer: EventTarget,
): void {
  const nativeEventTarget = getEventTarget(nativeEvent);
  const dispatchQueue: DispatchQueue = [];
  //創(chuàng)建合成事件，遍歷fiber鏈表，將會觸發(fā)的事件加入到dispatchQueue中
  extractEvents(
    dispatchQueue,
    domEventName,
    targetInst,
    nativeEvent,
    nativeEventTarget,
    eventSystemFlags,
    targetContainer,
  );
  //觸發(fā)時間隊(duì)列，執(zhí)行事件
  processDispatchQueue(dispatchQueue, eventSystemFlags);
}
//extractEvents
function extractEvents(
  dispatchQueue: DispatchQueue,  domEventName: DOMEventName,  targetInst: null | Fiber,  nativeEvent: AnyNativeEvent,  nativeEventTarget: null | EventTarget,  eventSystemFlags: EventSystemFlags,  targetContainer: EventTarget,
) {
  ...
  let from;
  let to;
  ...
  const leave = new SyntheticEventCtor(
    leaveEventType,
    eventTypePrefix + 'leave',
    from,
    nativeEvent,
    nativeEventTarget,
  );
  leave.target = fromNode;
  leave.relatedTarget = toNode;
  let enter: KnownReactSyntheticEvent | null = null;
  ...
  accumulateEnterLeaveTwoPhaseListeners(dispatchQueue, leave, enter, from, to);
}
//accumulateEnterLeaveTwoPhaseListeners
export function accumulateEnterLeaveTwoPhaseListeners(
  dispatchQueue: DispatchQueue,  leaveEvent: KnownReactSyntheticEvent,  enterEvent: null | KnownReactSyntheticEvent,  from: Fiber | null,  to: Fiber | null,
): void {
  const common = from && to ? getLowestCommonAncestor(from, to) : null;
  if (from !== null) {
    accumulateEnterLeaveListenersForEvent(
      dispatchQueue,
      leaveEvent,
      from,
      common,
      false,
    );
  }
  if (to !== null && enterEvent !== null) {
    accumulateEnterLeaveListenersForEvent(
      dispatchQueue,
      enterEvent,
      to,
      common,
      true,
    );
  }
}
// accumulateEnterLeaveListenersForEvent
function accumulateEnterLeaveListenersForEvent(
  dispatchQueue: DispatchQueue,  event: KnownReactSyntheticEvent,  target: Fiber,  common: Fiber | null,  inCapturePhase: boolean,
): void {
  // 獲取注冊的事件名
  const registrationName = event._reactName;
  // 事件處理函數(shù)容器
  const listeners: Array<DispatchListener> = [];
  //節(jié)點(diǎn)實(shí)例
  let instance = target;
  // 遍歷fiber，獲取fiber上的事件對應(yīng)的事件處理函數(shù)
  while (instance !== null) {
    if (instance === common) {
      break;
    }
    const {alternate, stateNode, tag} = instance;
    if (alternate !== null && alternate === common) {
      break;
    }
    if (tag === HostComponent && stateNode !== null) {
      const currentTarget = stateNode;
      // 根據(jù)捕獲階段，還是冒泡階段處理不同的函數(shù)邏輯
      if (inCapturePhase) {
        const captureListener = getListener(instance, registrationName);
        if (captureListener != null) {
          // 加入到listeners中
          // instance:當(dāng)前fiebr實(shí)例
          // currentTarget:當(dāng)前dom
          listeners.unshift(
            createDispatchListener(instance, captureListener, currentTarget),
          );
        }
      } else if (!inCapturePhase) {
        // 冒泡
        const bubbleListener = getListener(instance, registrationName);
        if (bubbleListener != null) {
          // 加入到listeners中
          listeners.push(
            createDispatchListener(instance, bubbleListener, currentTarget),
          );
        }
      }
    }
    // 當(dāng)前fiber實(shí)例的父級
    instance = instance.return;
  }
  if (listeners.length !== 0) {
    // 把事件、事件處理函數(shù)全部推到dispatchQueue中
    dispatchQueue.push({event, listeners});
  }
}
// processDispatchQueue
export function processDispatchQueue(
  dispatchQueue: DispatchQueue, // 事件隊(duì)列
  eventSystemFlags: EventSystemFlags, // 事件類型標(biāo)記
): void {
  const inCapturePhase = (eventSystemFlags & IS_CAPTURE_PHASE) !== 0;
  for (let i = 0; i < dispatchQueue.length; i++) {
    const {event, listeners} = dispatchQueue[i];
    // 執(zhí)行事件，完成觸發(fā)
    processDispatchQueueItemsInOrder(event, listeners, inCapturePhase);
    //  event system doesn't use pooling.
  }
  // This would be a good time to rethrow if any of the event handlers threw.
  rethrowCaughtError();
}