title: vue.js i used 'v-once' in 'v-for' statement,why can't find 'item'?
body: <pre><code>&lt;div v-for=&quot;item in imControls.messages&quot; &gt;
      &lt;p v-once&gt;
          &lt;span class=&quot;&quot; v-if=&quot;item.type==3&quot;&gt;{{item.name}}:&lt;/span&gt;
          &lt;span class=&quot;red&quot; v-if=&quot;item.type==4&quot;&gt;{{item.name}}:&lt;/span&gt;
          &lt;span class=&quot;blue&quot; v-if=&quot;item.type==2&quot;&gt;{{item.name}}:&lt;/span&gt;
          &lt;span class=&quot;grey&quot; v-if=&quot;item.type==1&quot;&gt;{{item.name}}:&lt;/span&gt;
          &lt;span v-html=&quot;item.text&quot;&gt;&lt;/span&gt;
      &lt;/p&gt;
   &lt;/div&gt;
  </code></pre>
  <p><code>imControls.messages</code> exists, if I don't use <code>v-once</code> on <code>p</code> label, it's ok, but if I use <code>v-once</code>, it can't find item.</p>
  <p>The error is</p>
  <blockquote>
  <p>'vue.js:2574 [Vue warn]: Property or method &quot;item&quot; is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option. (found in root instance)</p>
  <p>vue.js:2217 Uncaught TypeError: Cannot read property 'type' of undefined'</p>
  </blockquote>