title: Mutating object properties within an array with Polymer
body: <p>I not sure how to solve this issue. I am sure someone will know this very quickly.</p>
  
  <p>I have an array of objects and modifying a property. I have a firebase listener 'child_changed'. When firebase is updated need to update the array. Here is the code below.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>     dbRefList.on('child_changed', function(snap) {
            
            var len = this.grocerylist.length;
            for(var i=len; i--;) {
     
              if(this.grocerylist[i].key === snap.key) {
                this.set(['grocerylist', i, 'selected'], snap.val().selected);
              }
            }
          
            this.notifyPath('grocerylist', this.grocerylist.slice());
  
          }.bind(this));</code></pre>
  </div>
  </div>
  </p>
  
  <p>When the array is modified I want the template repeat-dom to trigger. I know this.set will not trigger array mutation sub properties but again I am not sure how to solve this. I done research and tried so many solutions.</p>
  
  <p>I can force a render on the template dom-repeat but I would prefer the data binding way.</p>