title: Firebase - child_added being called on delete of item
body: <p>I have a list of <code>post</code>'s and I'm fetching them with <code>.on('child_added')</code> the problem is that I only want to get the <code>post</code>'s when an item is <em>added</em> and not when it is <em>removed</em>, however, it seems that <code>.on('child_added')</code> gets called even when a post is removed. Which is not what I need in my case. </p>
  
  <p>Here is my function:</p>
  
  <pre><code>if(fromClick) { this.subscription.off(); this.firstRun = true;}
  this.postFeed = new Array();
  this.subscription = this.database.database.ref('/posts/'+this.locationId)
     .orderByChild('created')
     .limitToLast(10);
  
  this.subscription.on('child_added', (snapshot) =&gt; {
     this.postFeed.push(snapshot.val());
  });
  </code></pre>
  
  <p>So it displays last <code>10</code> and then when an item is added it adds that to the array as well, but when an item is removed it gets called again.. </p>
  
  <p>How can I prevent this? So that the call only happens for <code>post</code>'s that are added?</p>