title: Property or method "handleSelect" is not defined on the instance but referenced during render
body: <p>I'm using the <a href="http://element.eleme.io/#/en-US/component/menu#navmenu" rel="nofollow noreferrer">Element-UI component NavMenu</a> in order to create a nav bar in my web application. I'm using Vue.JS + TypeScript.</p>
  <p>So I've created a Vue component in a folder &quot;navBar&quot;, inside it I've:</p>
  <p>The component <code>navBar.vue</code>:</p>
  <pre><code>&lt;template src=&quot;./navBar.html&quot;&gt;
  &lt;/template&gt;
  &lt;script src=&quot;./navBar.ts&quot; lang=&quot;ts&quot;&gt;
  &lt;/script&gt;
  </code></pre>
  <p>The html <code>navBar.html</code>:</p>
  <pre><code>&lt;div id=&quot;navbar&quot;&gt;
    &lt;el-menu
      mode=&quot;horizontal&quot;
      :select=&quot;handleSelect&quot;
      background-color=&quot;rgba(95, 75, 139, 1)&quot;
      text-color=&quot;#fff&quot;
      active-text-color=&quot;rgba(255, 255, 255, 1)&quot;&gt;
      &lt;el-menu-item index=&quot;1&quot;&gt;Item 1&lt;/el-menu-item&gt;
    &lt;/el-menu&gt;
  &lt;/div&gt;
  </code></pre>
  <p>And the TypeScript <code>navBar.ts</code>:</p>
  <pre><code>import Vue from 'vue'
  import Component from 'vue-class-component'
  
  export default class NavBar extends Vue {
  
    handleSelect (key: string, keyPath: string) {
      console.log(key, keyPath)
    }
  
  }
  </code></pre>
  <p>But when I click on the <em>&quot;Item 1&quot;</em> I get the error:</p>
  <pre><code>[Vue warn]: Property or method &quot;handleSelect&quot; is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property. See: https://v2.vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties.
  </code></pre>
  <p>I can't explain why, any idea?</p>
  <p>I've already seen other questions like <a href="https://stackoverflow.com/questions/42908525/vue-warn-property-or-method-is-not-defined-on-the-instance-but-referenced-dur">this</a> but no one used TypeScript.</p>