title: How to make ref in component link to component data?
body: <p>I am using <a href="https://github.com/r3code/vue-vis-network" rel="nofollow noreferrer">https://github.com/r3code/vue-vis-network</a> 
  I am getting error: <code>Cannot read property 'hasChildNodes' of undefined</code></p>
  
  <p>My component code is:</p>
  
  <pre><code>&lt;template&gt;
      &lt;el-container &gt;
              &lt;el-main&gt;
                  &lt;network ref="network" :nodes="nodes" :edges="edges" :options="options"&gt; &lt;/network&gt;                        
                  &lt;button @click="get_data"&gt;GetData&lt;/button&gt;
              &lt;/el-main&gt;
    &lt;/el-container&gt;
  &lt;/template&gt;
  
  &lt;script&gt;
      export default {
          components: { Notification },
          data () {
              return {
                nodes: [],
                edges: [],
                options: []
              }
          },
  
          methods:
          {
            get_data()
            {
              axios.get(base_url + '/graph')
                 .then((response) =&gt; {
                  this.nodes = response.data.nodes;
                  this.edges = response.data.edges;
                  }).catch((error) =&gt; {   console.log(error); });  
            }
          },
      }
  &lt;/script&gt;
  </code></pre>
  
  <p>index.js:</p>
  
  <pre><code>Vue.component('network', new vueVisNetwork.Network);
  </code></pre>
  
  <p>I suppose that there is problem that it's attempt to access to data placed in #app. How I can say him that he should use data declared in component? </p>
  
  <p>Actual data example:</p>
  
  <pre><code>  nodes : [
      {id: 1, label: 'Fooo"', group: "company"},
      {id: 2, label: 'Baaar', group: "owner"},
    ],
  
  
    edges : [
      {from: 1, to: 2},
    ],
  </code></pre>
  
  <p>possible related issue <a href="https://github.com/crubier/react-graph-vis/issues/57" rel="nofollow noreferrer">https://github.com/crubier/react-graph-vis/issues/57</a></p>