title: Missing two-way data binding and computed property - Riot.js
body: <p>Even though I know I can add some events to update some of my variables using "event.target", how average could be updated when changing some of the scores, given the example below?</p>
  
  <pre><code> &lt;my-tag&gt;
      &lt;virtual each="{ criterias }"&gt;
          &lt;label for="{ name }"&gt;{ name }:&lt;/label&gt;
          &lt;input type="number" min="0" max="10" value="{ score }" name="{ name }" id="{ name }"&gt;
      &lt;/virtual&gt;
      &lt;p&gt;Average: { average }&lt;/p&gt;
  
      &lt;script&gt;
          this.criterias = [
          {
              name: 'Plot',
              score: 8
          },
          {
              name: 'Audio',
              score: 9
          },
          {
              name: 'Graphics',
              score: 7
          }
          ]
  
          this.average = this.criterias.reduce((a, b) =&gt; a + b['score'], 0) / this.criterias.length
      &lt;/script&gt;
  &lt;/my-tag&gt;
  </code></pre>