title: How to get key value in tab (element-ui)?
body: <p>How I could get the key value while clicking each tab? I can use obj.label to get label, but cannot use obj.key to get key. How?
  Code below is for the information.</p>
  
  <pre><code>&lt;el-tabs tab-position="left" @tab-click="handleClick"&gt;
    &lt;el-tab-pane v-for="u in planner" :label="u.name" :key="u.id" &gt;&amp;nbsp;&lt;/el-tab-pane&gt;
  &lt;/el-tabs&gt;
  
  handleClick(obj, e) {
    console.log(obj.label)  
    console.log(obj.key)  
  },
  </code></pre>