title: Cannot get a CSS property value of a flexible element with Vue
body: <p>I'm trying to get CSS <code>width</code> property of a flexible element, but for some reason it doesn't work:</p>
  <p>Codepen: <a href="https://codepen.io/anon/pen/pLEwdp?editors=1010" rel="nofollow noreferrer">https://codepen.io/anon/pen/pLEwdp?editors=1010</a></p>
  <hr />
  <h3>Code:</h3>
  <pre class="lang-html prettyprint-override"><code>&lt;v-layout&gt;
    &lt;h2 class=&quot;pa-3&quot;&gt;non-flex&lt;/h2&gt;
  
    &lt;v-spacer class=&quot;flexible-area grey&quot; ref=&quot;flexibleArea&quot;&gt;
      &lt;h2 class=&quot;pa-3&quot;&gt;current width is: {{flexibleAreaWidth}}&lt;/h2&gt;
    &lt;/v-spacer&gt;
  
    &lt;h2 class=&quot;pa-3&quot;&gt;non-flex&lt;/h2&gt;
  &lt;/v-layout&gt;
  
  ...
  
  computed: {
    flexibleAreaWidth () {
      let elem = this.$refs.flexibleArea
      return window.getComputedStyle(elem,null).getPropertyValue(&quot;width&quot;)
    }
  }
  </code></pre>