const counter = (state = 0, action) => {
  if (action.type === 'INCREMENT') {
    return state + 1;
  } else if (action.type === 'DECREMENT') {
    return state - 1;
  } else {
    return state;
  }
}


const Counter = ({
  value,
  onIncrement,
  onDecrement
}) => (
  <div>
    <h1>{value}</h1>
    <button onClick={onIncrement}>+</button>
    <button onClick={onDecrement}>-</button>
  </div>
);

const { createStore } = Redux;

const store = Redux.createStore(counter);

const render = () => {
  ReactDOM.render(
    <Counter
      value={store.getState()}
      onIncrement={() =>
        store.dispatch({type: 'INCREMENT'})
      }
      onDecrement={() =>
        store.dispatch({type: 'DECREMENT'})
      }
    />,
    document.getElementById('root')
  );
};

store.subscribe(render);
render();