title: Vue 3 and Mixin: this.$el.querySelectorAll is not a function
body: <p>When I try this:</p>
  <pre><code>createApp(App).mixin({
      methods: {
          myFunction() {
              this.$el.querySelectorAll('input').forEach(...);
          }
      },
  
      mounted() {
          this.myFunction();
      }
  }).mount('#app');
  </code></pre>
  <p>I'm getting a <code>TypeError: this.$el.querySelectorAll is not a function</code> but the weird thing is that everything is working as expected. So this.$el is defined, querySelectorAll() returns the nodes and I can iterate through them with forEach(). What is wrong here, how do I get rid of the error?</p>