extractEvents() — react Function Reference

Source Code

packages/react-dom-bindings/src/events/plugins/EnterLeaveEventPlugin.js lines 48–171

function extractEvents(
  dispatchQueue: DispatchQueue,
  domEventName: DOMEventName,
  targetInst: null | Fiber,
  nativeEvent: AnyNativeEvent,
  nativeEventTarget: null | EventTarget,
  eventSystemFlags: EventSystemFlags,
  targetContainer: EventTarget,
) {
  const isOverEvent =
    domEventName === 'mouseover' || domEventName === 'pointerover';
  const isOutEvent =
    domEventName === 'mouseout' || domEventName === 'pointerout';

  if (isOverEvent && !isReplayingEvent(nativeEvent)) {
    // If this is an over event with a target, we might have already dispatched
    // the event in the out event of the other target. If this is replayed,
    // then it's because we couldn't dispatch against this target previously
    // so we have to do it now instead.
    const related =
      (nativeEvent: any).relatedTarget || (nativeEvent: any).fromElement;
    if (related) {
      // If the related node is managed by React, we can assume that we have
      // already dispatched the corresponding events during its mouseout.
      if (
        getClosestInstanceFromNode(related) ||
        isContainerMarkedAsRoot(related)
      ) {
        return;
      }
    }
  }

  if (!isOutEvent && !isOverEvent) {
    // Must not be a mouse or pointer in or out - ignoring.
    return;
  }

  let win;
  // TODO: why is this nullable in the types but we read from it?
  if ((nativeEventTarget: any).window === nativeEventTarget) {
    // `nativeEventTarget` is probably a window object.
    win = nativeEventTarget;
  } else {
    // TODO: Figure out why `ownerDocument` is sometimes undefined in IE8.
    const doc = (nativeEventTarget: any).ownerDocument;
    if (doc) {
      win = doc.defaultView || doc.parentWindow;
    } else {
      win = window;
    }
  }

  let from;
  let to;
  if (isOutEvent) {
    const related = nativeEvent.relatedTarget || (nativeEvent: any).toElement;
    from = targetInst;
    to = related ? getClosestInstanceFromNode((related: any)) : null;
    if (to !== null) {
      const nearestMounted = getNearestMountedFiber(to);
      const tag = to.tag;
      if (
        to !== nearestMounted ||
        (tag !== HostComponent && tag !== HostSingleton && tag !== HostText)
      ) {
        to = null;
      }
    }
  } else {
    // Moving to a node from outside the window.
    from = null;
    to = targetInst;
  }

  if (from === to) {
    // Nothing pertains to our managed components.
    return;
  }

  let SyntheticEventCtor = SyntheticMouseEvent;