title: how to get the "index-as" value from html to javascript through on-tap function?
body: <p>I tried this but it is not working, the parentIndex value is not defined in javascript
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  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>_addAttribute: function(e) {
    console.log(e.model.parentIndex);
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>I wrote html like this
  
  &lt;paper-button on-tap="_addAttribute(this.parentIndex)"&gt;Add&lt;/paper-button&gt;
  &lt;template id="[[count]]" is="dom-repeat" items="{{parameters}}" index-as="parentIndex" restamp&gt;</code></pre>
  </div>
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  </p>