Redux Demo

npm install --save redux

import redux from 'redux';

const reducer = (state = { counter: 0 }, action) => {
    switch (action.type) {
        case 'INCREMENT':
            return { counter: state.counter + 1 };
        case 'DECREMENT':
            return { counter: state.counter - 1 };
        default:
            return state;
    }
};

const subscriber = () => {
    const latestState = store.getState();
    console.log(latestState);
};

const store = redux.createStore(reducer);
store.subscribe(subscriber);

store.dispatch({ type: 'INCREMENT' });
store.dispatch({ type: 'INCREMENT' });
store.dispatch({ type: 'DECREMENT' });
store.dispatch({ type: 'DECREMENT' });

Output:

{ counter: 1 }
{ counter: 2 }
{ counter: 1 }
{ counter: 0 }