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

Core utilities for building navigators

"use strict";

import * as React from 'react';
import useLatestCallback from 'use-latest-callback';
import { deepFreeze } from "./deepFreeze.js";
const createStore = getInitialState => {
  const listeners = [];
  let initialized = false;
  let state;
  const getState = () => {
    if (initialized) {
      return state;
    }
    initialized = true;
    state = deepFreeze(getInitialState());
    return state;
  };
  let isBatching = false;
  let didUpdate = false;
  const setState = newState => {
    state = deepFreeze(newState);
    didUpdate = true;
    if (!isBatching) {
      listeners.forEach(listener => listener());
    }
  };
  const subscribe = callback => {
    listeners.push(callback);
    return () => {
      const index = listeners.indexOf(callback);
      if (index > -1) {
        listeners.splice(index, 1);
      }
    };
  };
  const batchUpdates = callback => {
    isBatching = true;
    callback();
    isBatching = false;
    if (didUpdate) {
      didUpdate = false;
      listeners.forEach(listener => listener());
    }
  };
  return {
    getState,
    setState,
    batchUpdates,
    subscribe
  };
};
export function useSyncState(getInitialState) {
  const store = React.useRef(createStore(getInitialState)).current;
  const state = React.useSyncExternalStore(store.subscribe, store.getState, store.getState);
  React.useDebugValue(state);
  const pendingUpdatesRef = React.useRef([]);
  const scheduleUpdate = useLatestCallback(callback => {
    pendingUpdatesRef.current.push(callback);
  });
  const flushUpdates = useLatestCallback(() => {
    const pendingUpdates = pendingUpdatesRef.current;
    pendingUpdatesRef.current = [];
    if (pendingUpdates.length !== 0) {
      store.batchUpdates(() => {
        // Flush all the pending updates
        for (const update of pendingUpdates) {
          update();
        }
      });
    }
  });
  return {
    state,
    getState: store.getState,
    setState: store.setState,
    scheduleUpdate,
    flushUpdates
  };
}
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