import React, { Component, PropTypes } from 'react'
import ReactDOM from 'react-dom'

const increment = ({ count }) => ({ count: count + 1 });
const decrement = ({ count }) => ({ count: count - 1 });

class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }

  render() {
    return (
      <p>
        {this.state.count}
        <button onClick={() => this.setState(increment)}>+</button>
        <button onClick={() => this.setState(decrement)}>-</button>
      </p>
    );
  }
}

ReactDOM.render(<Counter />, document.getElementById('root'));