概览

beginWork

function beginWork(current, workInProgress, renderLanes) {
  if (current != null) {
   // 有旧Fiber，说明是更新操作，对比是否需要更新
    
    // 对比新旧props
    if (current.memoizedProps !== workInProgress.pendingProps) {
      didReceiveUpdate = true;// 表示需要更新
    } else {
      // 若Props不同，则检查是否有计划的更新或context变化
      const hasScheduledUpdateOrContext = checkScheduledUpdateOrContext(
        current,
        renderLanes,
      );
      if (
        !hasScheduledUpdateOrContext &&
        (workInProgress.flags & DidCapture) === NoFlags
      ) {
        // 没有更新且没有捕获错误，尝试提前退出

        didReceiveUpdate = false;
        return attemptEarlyBailoutIfNoScheduledUpdate(
          current,
          workInProgress,
          renderLanes,
        );
      }
      
      // 检查是否有强制更新 用于Legacy Suspense
      if ((current.flags & ForceUpdateForLegacySuspense) !== NoFlags) {
        didReceiveUpdate = true;
      } else {
        didReceiveUpdate = false;
      }
    }
  } else {
    // 没有旧Fiber，是首次渲染
    didReceiveUpdate = false;

    // 处理Hydration相关逻辑
    if (getIsHydrating() && isForkedChild(workInProgress)) {
      const slotIndex = workInProgress.index;
      const numberOfForks = getForksAtLevel(workInProgress);
      pushTreeId(workInProgress, numberOfForks, slotIndex);
    }
  }
  
  // 重置工作 Fiber 的 lanes
  workInProgress.lanes = NoLanes;
  switch (workInProgress.tag) {
  }
}