title: what does this.$root means in a component?
body: <p>I have a main App.vue component. in there, I have the following code:</p>
  
  <pre><code>export default {
    data() {
      return {
        testVariable:false
      }
    },
  }
  &lt;/script&gt;
  
  &lt;template&gt;
    &lt;VApp :dark="testVariable:false"
      &lt;div id="app"&gt;
        &lt;RouterView :key="$route.fullPath" /&gt;
      &lt;/div&gt;
    &lt;/VApp&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>Then in one of the components, I have the following code:</p>
  
  <pre><code>data() {
      return {
        testVariable: this.$root.$children[0].testVariable,
      }
    },
  
  methods: {
      darkModeToggle(e) {
        this.$root.$children[0].testVariable = e
      },
    },
  </code></pre>
  
  <p>Question 1) What does this.$root and this.$root.children mean? is <code>this.$root</code> always App.vue component(because App.vue is the parent of all components).  is <code>this.$root.children</code> the children of this App.vue component which means all other components will be in <code>this.$root.children</code> array?</p>
  
  <p>Question 2) What does this line mean?<code>&lt;RouterView :key="$route.fullPath" /&gt;</code> . I mean why do we pass <code>:key="$route.fullPath"?</code></p>