title: ReferenceError: ok is not defined
body: <p>i recently learning about <code>vue</code>
  I have this file <code>index.html</code></p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;title&gt;Learning Vue Js&lt;/title&gt;
      &lt;link rel="stylesheet" type="text/css" href="style.css"&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;div id="root"&gt; 
      &lt;button @click="show = !show"&gt;Toggle&lt;/button&gt;
      &lt;div class="foo" v-show="ok"&gt;
          &lt;p&gt;ok&lt;/p&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  
  &lt;script src="https://cdn.jsdelivr.net/npm/vue"&gt;&lt;/script&gt;
  
  &lt;script type="text/javascript"&gt;
      var app = new Vue({
      el: "#root",
      data: {
          ok: false
      }
  });
  
  &lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>