title: How to check if an object is a firestore.Timestamp?
body: <p>I'm working on a validation function.</p>
  <p>Is there a way to check if an object is a <code>firestore.Timestamp</code> ?</p>
  <p>I'm using the <code>firebase</code> JS SDK and also using Typescript.</p>
  <pre><code>import * as firebase from &quot;firebase/app&quot;;
  
  const blogPost = {
    title: &quot;&quot;,
    createdAt: firebase.firestore.Timestamp.now()
  }
  
  function validateBlogPostCreationDate(blogPost) {
    // SOMETHING LIKE THIS:
    return blogPost.createdAt is a Timestamp ?
      true : false;
  }
  </code></pre>