Function requestDeferredLane

packages/react-reconciler/src/ReactFiberWorkLoop.js:852–889

()

}

export function requestDeferredLane(): Lane {
  if (workInProgressDeferredLane === NoLane) {
    // If there are multiple useDeferredValue hooks in the same render, the
    // tasks that they spawn should all be batched together, so they should all
    // receive the same lane.

    // Check the priority of the current render to decide the priority of the
    // deferred task.

    // OffscreenLane is used for prerendering, but we also use OffscreenLane
    // for incremental hydration. It's given the lowest priority because the
    // initial HTML is the same as the final UI. But useDeferredValue during
    // hydration is an exception — we need to upgrade the UI to the final
    // value. So if we're currently hydrating, we treat it like a transition.
    const isPrerendering =
      includesSomeLane(workInProgressRootRenderLanes, OffscreenLane) &&
      !getIsHydrating();
    if (isPrerendering) {
      // There's only one OffscreenLane, so if it contains deferred work, we
      // should just reschedule using the same lane.
      workInProgressDeferredLane = OffscreenLane;
    } else {
      // Everything else is spawned as a transition.
      workInProgressDeferredLane = claimNextTransitionDeferredLane();
    }
  }

  // Mark the parent Suspense boundary so it knows to spawn the deferred lane.
  const suspenseHandler = getSuspenseHandler();
  if (suspenseHandler !== null) {
    // TODO: As an optimization, we shouldn't entangle the lanes at the root; we
    // can entangle them using the baseLanes of the Suspense boundary instead.
    // We only need to do something special if there's no Suspense boundary.
    suspenseHandler.flags |= DidDefer;
  }

  return workInProgressDeferredLane;
}

export function scheduleViewTransitionEvent(
  fiber: Fiber,