app.vue
export default {
  data() {
    return {
    }
  },
  methods: {
    Teaching(){
      alert("")
    }
  }
};a.js
import Vue from "vue"
import App from "./app"
const app = new Vue({
  el: "-sharpapp",
  render: h => h(App)
})a.html
<!DOCTYPE html>
<html>
<head>
    <title></title>
</head>
<body>
    <div id="app"></div>
</body>
</html> code is the 
 above. Now I want to write a function in  a.html . This function needs to call the  Teaching  function in  methods  of  vue  in  app.vue , which looks something like this: 
a.html
<!DOCTYPE html>
<html>
<head>
    <title></title>
</head>
<body>
    <div id="app"></div>
    <script>
        function iframe_connect(){
            //Teaching
            app.Teaching()//
        }
    </script>
</body>
</html>do not know what to do, ask for advice
