title: Which Data Type does Firestore use for it's Timestamps?
body: <p>I'm sure anyone who already knows will think this is an obvious question but I've already spent a lot of time searching the docs for this.</p>
  
  <p>I would think you do something like this, but this doesn't work:</p>
  
  <pre><code>import * as firebase from 'firebase/app';
  
  export interface ChatMessage {
    message: string;
    dateSent: firebase.firestore.serverTimestamp();
  }
  </code></pre>
  
  <p>Also, I've seen this in some places, but it doesn't work for me either...</p>
  
  <pre><code>firebase.firestore.FieldValue.serverTimestamp();
  </code></pre>
  
  <p>I just get <code>Namespace 'firebase.firestore' has no exported member 'FieldValue'.</code></p>