title: format date as long inside reactjs component
body: <p>I have a component like this</p>
  
  <pre><code>var Post = React.createClass({
  
  
  render: function () {
      return (
        &lt;li key={ this.props.message.uid }&gt;
          &lt;div className="avatar"&gt;
            &lt;img src={ this.props.message.user.avatar } className="img-circle"/&gt;
          &lt;/div&gt;
          &lt;div className="messages"&gt;
            &lt;p&gt;{ this.props.message.content }&lt;/p&gt;
            &lt;span className="date"&gt;{ "@"+this.props.message.user.login + " • " }&lt;/span&gt;
            &lt;span className="date timeago" title={ this.props.message.createdAt }&gt;
              { this.props.message.createdAt }
            &lt;/span&gt;
          &lt;/div&gt;
        &lt;/li&gt;
        )
    }
  });
  </code></pre>
  
  <p>turns out that the <code>createdAt</code> is a string like <code>1451589259845</code> and I want to format the date. How can I do that on ReactJS? I tried put <code>new Date()</code> inside the brackets but got an error.</p>