title: Listen only to additions to a cloud firestore collection?
body: <p>I've noticed, when I try to use a realtime listener on a Collection in firestore, each time a new Document is added to the collection, the logic will be rerun, and I will download everything already in the collection</p>
  
  <p>right now:</p>
  
  <pre><code>firebase.firestore().collection("Tweets").onSnapshot(function(querySnapshot) {
        querySnapshot.forEach(function(doc) {
          console.log("snapshot added ", doc)
        });
      });
  </code></pre>
  
  <p>Is there a way to track only ADDITIONS to the collection? I guess I could do that device side, but theres no need to transfer all the additional data I have already queryed for..</p>
  
  <p>Output of that log would print out every single "tweet" in the collection, regardless of only one being added</p>
  
  <p>EX:
  Initial Query</p>
  
  <p>-Tweet 1 </p>
  
  <p>-Tweet 2</p>
  
  <p>-Tweet 3</p>
  
  <p>New Tweet, Tweet 4 is added</p>
  
  <p>Output:</p>
  
  <p>Tweet 1</p>
  
  <p>Tweet 2</p>
  
  <p>Tweet 3</p>
  
  <p>Tweet 4</p>
  
  <p>If that makes sense</p>