A simple state manager

example.ts

import {createStore} from './store';

const [store, watch] = createStore({ counter: 1 });

watch((data) => {
    console.log(data.counter);
});

store.counter += 1;
store.counter += 1;

store.ts

type StoreWatcher<T> = (data: T) => void;

export function createStore<T>(init: T & Record<string, any>): [T, (fn: StoreWatcher<T>, run?: boolean) => void] {
    const t: T | Record<string, any> = {}, store: Record<string, any> = {};
    const watcher: StoreWatcher<T>[] = [];

    Object.keys(init).forEach((key: string) => {
        store[key] = init[key];

        Object.defineProperty(t, key, {
            enumerable: true,
            set: (v) => {
                store[key] = v;
                watcher.forEach((fn) => fn(t as T));
            },
            get: () => store[key]
        });
    });

    function watch(fn: StoreWatcher<T>, run = true) {
        watcher.push(fn);

        if (run) {
            fn(store as T);
        }
    }

    return [t as T, watch];
}