Button.jsx

import React from 'react';
import { render } from 'react-dom';

class Button extends React.Component {
  handleClick = () => {
    this.props.onClick(this.props.value)
  }

  render() {
    return <button {...this.props} onClick={this.handleClick} />
  }
}

render((
  <Button
    value="Hello"
    onClick={() => console.log(value + ', world!')}
  >
    Button
  </Button>
), document.getElementById('root'))