Detailed explanation of small state management based on React Hooks

import {
  Dispatch,
  SetStateAction,
  useCallback,
  useEffect,
  useReducer,
  useRef,
  useState,
} from 'react';

/**
 * @see https://github.com/facebook/react/blob/bb88ce95a87934a655ef842af776c164391131ac/packages/shared/objectIs.js
 * inlined Object.is polyfill to avoid requiring consumers to ship their own
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
 */
function is(x: any, y: any): boolean {
  return (x === y && (x !== 0 || 1 / x === 1 / y)) || (x !== x && y !== y);
}

const objectIs = typeof Object.is === 'function' ? Object.is : is;

/**
 * @see https://github.com/facebook/react/blob/933880b4544a83ce54c8a47f348effe725a58843/packages/shared/shallowEqual.js
 * Performs equality by iterating through keys on an object and returning false
 * when any key has values ​​which are not strictly equal between the arguments.
 * Returns true when the values ​​of all keys are strictly equal.
 */
function shallowEqual(objA: any, objB: any): boolean {
  if (is(objA, objB)) {
    return true;
  }

  if (
    typeof objA !== 'object' ||
    objA === null ||
    typeof objB !== 'object' ||
    objB === null
  ) {
    return false;
  }

  const keysA = Object.keys(objA);
  const keysB = Object.keys(objB);

  if (keysA.length !== keysB.length) {
    return false;
  }

  // Test for A's keys different from B.
  for (let i = 0; i < keysA.length; i++) {
    if (
      !Object.prototype.hasOwnProperty.call(objB, keysA[i]) ||
      !is(objA[keysA[i]], objB[keysA[i]])
    ) {
      return false;
    }
  }

  return true;
}

const useForceUpdate = () => useReducer(() => ({}), {})[1] as VoidFunction;

type ISubscriber<T> = (prevState: T, nextState: T) => void;

export interface ISharedState<T> {
  /** Get data statically, suitable for use in non-components or when data is not bound to a view*/
  get: () => T;
  /** Modify data and assign new value*/
  set: Dispatch<SetStateAction<T>>;
  /** (Shallow) merge update data*/
  update: Dispatch<Partial<T>>;
  /** The hooks method obtains data, which is suitable for use in components. The component will be automatically re-rendered when the data changes*/
  use: () => T;
  /** Subscription data changes */
  subscribe: (cb: ISubscriber<T>) => () => void;
  /** Unsubscribe data changes */
  unsubscribe: (cb: ISubscriber<T>) => void;
  /** Filter out some states */
  usePick<R>(picker: (state: T) => R, deps?: readonly any[]): R;
}

export type IReadonlyState<T> = Omit<ISharedState<T>, 'set' | 'update'>;

/**
 * Create a state that can be shared between different instances * @param initialState initial data */
export const createSharedState = <T>(initialState: T): ISharedState<T> => {
  let state = initialState;
  const subscribers: ISubscriber<T>[] = [];

  //Subscribe to state changes const subscribe = (subscriber: ISubscriber<T>) => {
    subscribers.push(subscriber);
    return () => unsubscribe(subscriber);
  };

  // Unsubscribe from state changes const unsubscribe = (subscriber: ISubscriber<T>) => {
    const index = subscribers.indexOf(subscriber);
    index > -1 && subscribers.splice(index, 1);
  };

  // Get the latest state
  const get = () => state;

  // Change state
  const set = (next: SetStateAction<T>) => {
    const prevState = state;
    // @ts-ignore
    const nextState = typeof next === 'function' ? next(prevState) : next;
    if (objectIs(state, nextState)) {
      return;
    }
    state = nextState;
    subscribers.forEach((cb) => cb(prevState, state));
  };

  //Get the latest state of hooks usage const use = () => {
    const forceUpdate = useForceUpdate();

    useEffect(() => {
      let isMounted = true;
      // Update the component immediately after mounting to avoid not being able to use the first updated data forceUpdate();
      const un = subscribe(() => {
        if (!isMounted) return;
        forceUpdate();
      });
      return () => {
        un();
        isMounted = false;
      };
    }, []);

    return state;
  };

  const usePick = <R>(picker: (s: T) => R, deps = []) => {
    const ref = useRef<any>({});

    ref.current.picker = picker;

    const [pickedState, setPickedState] = useState<R>(() =>
      ref.current.picker(state),
    );

    ref.current.oldState = pickedState;

    const sub = useCallback(() => {
      const pickedOld = ref.current.oldState;
      const pickedNew = ref.current.picker(state);
      if (!shallowEqual(pickedOld, pickedNew)) {
        // Avoid pickedNew being a function
        setPickedState(() => pickedNew);
      }
    }, []);

    useEffect(() => {
      const un = subscribe(sub);
      return un;
    }, []);

    useEffect(() => {
      sub();
    }, [...deps]);

    return pickedState;
  };

  return {
    get,
    set,
    update: (input: Partial<T>) => {
      set((pre) => ({
        ...pre,
        ...input,
      }));
    },
    use,
    subscribe,
    unsubscribe,
    usePick,
  };
};

// Create a state instance const countState = createSharedState(0);

const A = () => {
  //Use hooks in components to get responsive data const count = countState.use();
  return <div>A: {count}</div>;
};

const B = () => {
  // Use the set method to modify data return <button onClick={() => countState.set(count + 1)}>Add</button>;
};

const C = () => {
  return (
    <button
      onClick={() => {
        // Use the get method to get data console.log(countState.get());
      }}
    >
      Get
    </button>
  );
};

const App = () => {
  return (
    <>
      <A />
      <B />
      <C />
    </>
  );
};

const complexState = createSharedState({
  a: 0,
  b: {
    c: 0,
  },
});

const A = () => {
  const a = complexState.usePick((state) => state.a);
  return <div>A: {a}</div>;
};

/**
 * State derived (or computed)
 * ```ts
 * const count1 = createSharedState(1);
 * const count2 = createSharedState(2);
 * const count3 = createDerivedState([count1, count2], ([n1, n2]) => n1 + n2);
 * ```
 * @param stores
 * @param fn
 * @param initialValue
 * @returns
 */
export function createDerivedState<T = any>(
  stores: IReadonlyState<any>[],
  fn: (values: any[]) => T,
  opts?: {
    /**
     * Whether to respond synchronously * @default false
     */
    sync?: boolean;
  },
): IReadonlyState<T> & {
  stop: () => void;
} {
  const { sync } = { sync: false, ...opts };
  let values: any[] = stores.map((it) => it.get());
  const innerModel = createSharedState<T>(fn(values));

  let promise: Promise<void> | null = null;

  const uns = stores.map((it, i) => {
    return it.subscribe((_old, newValue) => {
      values[i] = newValue;

      if (sync) {
        innerModel.set(() => fn(values));
        return;
      }

      // Asynchronous update promise =
        promise ||
        Promise.resolve().then(() => {
          innerModel.set(() => fn(values));
          promise = null;
        });
    });
  });

  return {
    get: innerModel.get,
    use: innerModel.use,
    subscribe: innerModel.subscribe,
    unsubscribe: innerModel.unsubscribe,
    usePick: innerModel.usePick,
    stop: () => {
      uns.forEach((un) => un());
    },
  };
}

const countState = createSharedState(0);

const App = () => {
  useEffect(() => {
    setInterval(() => {
      console.log(countState.get());
    }, 1000);
  }, []);
  // return ...
};

const countState = createSharedState(0);

const Content = () => {
  const count = countState.use();
  return <div>{count}</div>;
};

const A = () => (
  <button
    onClick={() => {
      Dialog.info({
        title: 'Alert',
        content: <Content />,
      });
    }}
  >
    open
  </button>
);