redux-minimal-app.js

import React from 'react'
import ReactDOM from 'react-dom'
import { createStore } from 'redux'
import { Provider, connect } from 'react-redux'

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

const store = createStore(reducer)

const Counter = props =>
    <button onClick={props.onIncrement}>
        {props.value}
    </button>;

const CounterContainer = connect(
        state => ({ value: state.counter }),
        dispatch => ({ onIncrement: () => dispatch({type:'INCREMENT'}) })
)(Counter)

ReactDOM.render(
    <Provider store={store}>
        <CounterContainer />
    </Provider>,
    document.getElementById('app')
)