Edit in JSFiddle

var contacts = [
  {key: 1, name: "James K Nelson", email: "james@jamesknelson.com", description: "Front-end Unicorn"},
  {key: 2, name: "Jim", email: "jim@example.com"},
  {key: 3, name: "Joe"},
]

var ContactItem = React.createClass({
  propTypes: {
    name: React.PropTypes.string.isRequired,
    email: React.PropTypes.string.isRequired,
    description: React.PropTypes.string,
  },

  render: function() {
    // I wrap mult-line return statements in parentheses to avoid the
    // inevitable bugs caused by forgetting that JavaScript will throw away
    // the final lines when possible. The parentheses are not strictly
    // necessary.
    return (
      React.createElement('li', {},
        React.createElement('h2', {}, this.props.name),
        React.createElement('a', {href: 'mailto:'+this.props.email}, this.props.email),
        React.createElement('div', {}, this.props.description)
      )
    )
  },
})

var contactItemElements = contacts
  .filter(function(contact) { return contact.email })
  .map(function(contact) { return React.createElement(ContactItem, contact) })

var rootElement =
  React.createElement('div', {}, 
    React.createElement('h1', {}, "Contacts"),
    React.createElement('ul', {}, contactItemElements)
  )

ReactDOM.render(rootElement, document.getElementById('react-app'))

<div id="react-app"></div>
<script src="https://cdn.jsdelivr.net/react/0.14.0-rc1/react.js"></script>
<script src="https://cdn.jsdelivr.net/react/0.14.0-rc1/react-dom.js"></script>