create store

store.js

const store = (reducer) => {
  let state = []; // Can be an object as well
  let listeners = [];

  const dispatch = (action) => {
    state = reducer(state, action);
    listeners.forEach((listener) => listener(state));
  };

  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
      // To unsubscribe
      listeners.filter((l) => l !== listener);
    };
  };

  return { state, dispatch, subscribe };
};