title: How to add an object to an amp-state array in AMP-HTML?
body: <p>I have a state called currentItem with url, title, description... When I push a button, a currentItem should be saved in other state called myItems. It will contains a list of items objects.</p>
  
  <p>The problem right now is that it <b>always shows the last item</b>, so it is overwriting the entire list for each currentItem submit.</p>
  
  <p>My States:</p>
  
  <pre class="lang-html prettyprint-override"><code>    &lt;amp-state id="currentItem"&gt;
          &lt;script type="application/json"&gt;
              {
                  "url": "",
                  "imageUrl": "",
                  "title": "",
                  "description": ""
              }
          &lt;/script&gt;
      &lt;/amp-state&gt;
      &lt;amp-state id="myItems"&gt;
          &lt;script type="application/json"&gt;
              []
          &lt;/script&gt;
      &lt;/amp-state&gt;
  </code></pre>
  
  <p>The list definition:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;amp-list class="mt3"
            layout="fixed-height"
            height="0"
            [src]="myItems"
            [height]="myItems.length * 200"
            items="."
            binding="no"&gt;
  &lt;template type="amp-mustache"&gt;
  ...
  &lt;/template&gt;
  </code></pre>
  
  <p>The action to add currentItem to the list:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;button type="button"
          on="tap:AMP.setState({ myItems: [currentItem]})"&gt;
  Add
  &lt;/button&gt;
  </code></pre>
  
  <p>I tried using AMP.setState({ myItems: myItems.concat(currentItem)}) but it crash, also with +. How can I do that?</p>