Modal.jsx

import React, {Component, PropTypes} from 'react'

class Modal extends Component {
  state = {isOpen: false}

  static propTypes = {
    isOpen: PropTypes.bool
  }

  componentWillMount() {
    this.setState({isOpen: this.props.isOpen})
  }

  renderContent () {
    return (
      <div id="modal">
        <form>
          <input type="text" placeholder="Your e-mail" />
          
          <textarea placeholder="What are your thoughts?" />
          
          <button onClick={this.setState({isOpen: false})}>Close</button>
          <button>Send</button>
        </form>
      </div>
    )
  }

  render () {
    {isOpen} = this.state
    
    return isOpen ? this.renderContent() : null
  }
}

export default Modal