Function flushLayoutEffects

packages/react-reconciler/src/ReactFiberWorkLoop.js:3881–3978

()

}

function flushLayoutEffects(): void {
  if (pendingEffectsStatus !== PENDING_LAYOUT_PHASE) {
    return;
  }
  pendingEffectsStatus = NO_PENDING_EFFECTS;

  if (enableProfilerTimer && enableComponentPerformanceTrack) {
    const suspendedViewTransitionReason = pendingSuspendedViewTransitionReason;
    if (suspendedViewTransitionReason !== null) {
      // We suspended in the middle of the commit for the view transition.
      // We'll start a new commit track now.
      recordCommitTime();
      logSuspendedViewTransitionPhase(
        commitEndTime, // The start is the end of the first commit part.
        commitStartTime, // The end is the start of the second commit part.
        suspendedViewTransitionReason,
        animatingTask,
      );
    }
  }

  const root = pendingEffectsRoot;
  const finishedWork = pendingFinishedWork;
  const lanes = pendingEffectsLanes;

  if (enableDefaultTransitionIndicator) {
    const cleanUpIndicator = root.pendingIndicator;
    if (cleanUpIndicator !== null && root.indicatorLanes === NoLanes) {
      // We have now committed all Transitions that needed the default indicator
      // so we can now run the clean up function. We do this in the layout phase
      // so it has the same semantics as if you did it with a useLayoutEffect or
      // if it was reset automatically with useOptimistic.
      const prevTransition = ReactSharedInternals.T;
      ReactSharedInternals.T = null;
      const previousPriority = getCurrentUpdatePriority();
      setCurrentUpdatePriority(DiscreteEventPriority);
      const prevExecutionContext = executionContext;
      executionContext |= CommitContext;
      root.pendingIndicator = null;
      try {
        cleanUpIndicator();
      } catch (x) {
        reportGlobalError(x);
      } finally {
        // Reset the priority to the previous non-sync value.
        executionContext = prevExecutionContext;
        setCurrentUpdatePriority(previousPriority);
        ReactSharedInternals.T = prevTransition;
      }
    }
  }

  const subtreeHasLayoutEffects =
    (finishedWork.subtreeFlags & LayoutMask) !== NoFlags;
  const rootHasLayoutEffect = (finishedWork.flags & LayoutMask) !== NoFlags;

  if (subtreeHasLayoutEffects || rootHasLayoutEffect) {
    const prevTransition = ReactSharedInternals.T;