title: Return document data after set/add operation in Firestore
body: <p>I'm trying to get back some info about the document I just created/updated without making a second request.</p>
  
  <p>I know that I get back a Document reference with the Id of the document, but I need additional info like createTime and updateTime.</p>
  
  <p>Currently, this is the way I'm trying to achieve that, but I would like to spare that extra request since it's not very efficient.</p>
  
  <pre><code>const docRef = await database.collection('tagsCollection').add({
      ...input
      createTime: firestore.FieldValue.serverTimestamp()
  });
  
  const doc = await docRef.get();
  
  return {
      ...doc.data(),
      id: doc.id,
      createTime: doc.data().createTime.toMillis().toString()
  };
  </code></pre>