next
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The React Framework
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TypeScript
import type { FlightRouterState } from '../../server/app-render/types';
export type RouterBFCacheEntry = {
tree: FlightRouterState;
stateKey: string;
next: RouterBFCacheEntry | null;
};
/**
* Keeps track of the most recent N trees (FlightRouterStates) that were active
* at a certain segment level. E.g. for a segment "/a/b/[param]", this hook
* tracks the last N param values that the router rendered for N.
*
* The result of this hook precisely determines the number and order of
* trees that are rendered in parallel at their segment level.
*
* The purpose of this cache is to we can preserve the React and DOM state of
* some number of inactive trees, by rendering them in an <Activity> boundary.
* That means it would not make sense for the the lifetime of the cache to be
* any longer than the lifetime of the React tree; e.g. if the hook were
* unmounted, then the React tree would be, too. So, we use React state to
* manage it.
*
* Note that we don't store the RSC data for the cache entries in this hook —
* the data for inactive segments is stored in the parent CacheNode, which
* *does* have a longer lifetime than the React tree. This hook only determines
* which of those trees should have their *state* preserved, by <Activity>.
*/
export declare function useRouterBFCache(activeTree: FlightRouterState, activeStateKey: string): RouterBFCacheEntry;