title: Can I prevent Firebase set() from overwriting existing data?
body: <p>If I do this, all is good with my itemRef:</p>
  
  <pre><code>itemRef.child('appreciates').set(newFlag);
  itemRef.child('id').set(newId);
  </code></pre>
  
  <p>other properties of itemRef remain BUT child_changed is called twice</p>
  
  <p>If I do this:</p>
  
  <pre><code>itemRef.set({appreciates:newFlag,id:newId});
  </code></pre>
  
  <p>child_changed is called only once but my other properties are destroyed.
  Is there a workaround besides the clumsy one of repopulating the entire reference object?</p>
  
  <p>Thanks,</p>
  
  <p>Tim</p>