Components

import React from 'react'
import ReactDOM from 'react-dom'

class Hello extends React.Component {
  render () {
    return <div className='message-box'>
      Hello {this.props.name}
    </div>
  }
}

const el = document.body
ReactDOM.render(<Hello name='John' />, el)

Use the React.js jsfiddle to start hacking. (or the unofficial jsbin)