@react-navigation/core/lib/module/useSyncState.js

Core utilities for building navigators

import * as React from 'react';
const UNINTIALIZED_STATE = {};

/**
 * This is definitely not compatible with concurrent mode, but we don't have a solution for sync state yet.
 */
export default function useSyncState(initialState) {
  const stateRef = React.useRef(UNINTIALIZED_STATE);
  const isSchedulingRef = React.useRef(false);
  const isMountedRef = React.useRef(true);
  React.useEffect(() => {
    isMountedRef.current = true;
    return () => {
      isMountedRef.current = false;
    };
  }, []);
  if (stateRef.current === UNINTIALIZED_STATE) {
    stateRef.current =
    // @ts-expect-error: initialState is a function, but TypeScript doesn't think so
    typeof initialState === 'function' ? initialState() : initialState;
  }
  const [trackingState, setTrackingState] = React.useState(stateRef.current);
  const getState = React.useCallback(() => stateRef.current, []);
  const setState = React.useCallback(state => {
    if (state === stateRef.current || !isMountedRef.current) {
      return;
    }
    stateRef.current = state;
    if (!isSchedulingRef.current) {
      setTrackingState(state);
    }
  }, []);
  const scheduleUpdate = React.useCallback(callback => {
    isSchedulingRef.current = true;
    try {
      callback();
    } finally {
      isSchedulingRef.current = false;
    }
  }, []);
  const flushUpdates = React.useCallback(() => {
    if (!isMountedRef.current) {
      return;
    }

    // Make sure that the tracking state is up-to-date.
    // We call it unconditionally, but React should skip the update if state is unchanged.
    setTrackingState(stateRef.current);
  }, []);

  // If we're rendering and the tracking state is out of date, update it immediately
  // This will make sure that our updates are applied as early as possible.
  if (trackingState !== stateRef.current) {
    setTrackingState(stateRef.current);
  }
  const state = stateRef.current;
  React.useDebugValue(state);
  return [state, getState, setState, scheduleUpdate, flushUpdates];
}
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