content: import React from 'react'
  
  export const Counter = (props) => (
    <div style={{ margin: '0 auto' }} >
      <h2>Counter: {props.counter}</h2>
      <button className='btn btn-default' onClick={props.increment}>
        Increment
      </button>
      {' '}
      <button className='btn btn-default' onClick={props.doubleAsync}>
        Double (Async)
      </button>
    </div>
  )
  
  Counter.propTypes = {
    counter     : React.PropTypes.number.isRequired,
    doubleAsync : React.PropTypes.func.isRequired,
    increment   : React.PropTypes.func.isRequired
  }
  
  export default Counter
  